INCREASING RICE PRODUCTION IN SUB‐SAHARAN AFRICA: CHALLENGES AND OPPORTUNITIES

INCREASING RICE PRODUCTION IN

SUB‐SAHARAN AFRICA: CHALLENGES

AND OPPORTUNITIES

V. Balasubramanian,1,� M. Sie,2 R. J. Hijmans1 and K. Otsuka3,4

1International Rice Research Institute (IRRI), Metro Manila, Philippines2Africa Rice Center (WARDA), 01 BP 2031 Cotonou, Benin, West Africa

3Foundation for Advanced Studies on InternationalDevelopment (FASID), 7‐22‐1 Roppongi, Minatoku,

Tokyo 106‐8677, Japan4National Graduate Institute for Policy Studies, 7‐22‐1 Roppongi, Minatoku,

Tokyo 106‐8677, Japan

�PrPost, C

I.

esent

oimb

I

A

a

ntroduction

ddress: Freelance consultant, Ramya Illam, 42 Thadagam Road, Velandip

tore 641025, India.

55

Advances in Agronomy, Volume 94Copyright 2007, Elsevier Inc. All rights reserved.

0065-2113/07 $35.00DOI: 10.1016/S0065-2113(06)94002-4

II.
R ice Demand and Supply
III.
W etlands: The Potential Resource for Rice Production in SSA
A. D
efinition, Area, and Distribution of Wetlands
B. T
ypes and Characteristics of Wetlands
IV.
R ice Soil Resources
A. D
ryland Soils and Their Characteristics
B. W
etland Soils and Their Characteristics
V.
A groclimatic Zones and Rice Ecosystems
A. D
ryland Rice Ecosystems
B. W
etland Rice Ecosystems
VI.
R ice Production Constraints in SSA
A. P
hysical, Biological, and Management Constraints
B. H
uman Resource Constraints
C. S
ocioeconomic and Policy Constraints
VII.
R ice Research and Technology Development During
the Past 20 Years

A. R
ice Germplasm, Breeding, and Variety Development
B. R
ice Seed Production and Distribution Services
C. C
rop Establishment
D. N
utrient Management
E. W
ater Management for Rainfed and Irrigated Areas
F. W
eeds, Insect Pests, and Diseases and Their Management
G. G
rain Quality Management: From Breeding to Milling
alayam

56 V. BALASUBRAMANIAN ETAL.

H. D
iversification of Rice Farming Systems
I. IC
M for Rice
V
III. R ice Intensification Issues and Thoughts for the Future
A. R
ice Intensification in Relation to Vector‐Borne Human Diseases
B. E
nvironmental Issues Related to Rice Intensification in SSA
C. P
reparing for the Impact of Climate Change
D. T
echnology Delivery and Deployment Issues
E. P
olicy Support for Rice Intensification in SSA
IX.
C onclusions: Challenges to and Opportunities for Enhancing
Rice Production in SSA

A
cknowledgments
R
eferences
Sub‐Saharan Africa (SSA) faces multiple problems. The main one is

improving the lives of the 30% of its population that suVers from extreme

poverty and food insecurity. As more than 70% of the population lives oVfarming and related activities, agricultural development will have to play a

major role in improving this situation. Fortunately, Africa has an abundant

supply of natural resources that can support a huge expansion in food,

specifically rice production. Because of strong demand, rice area expansion

in SSA is larger than for any other crop. Total milled rice production

increased from 2.2 millionMg in 1961 to 9.1 millionMg in 2004. Rice imports

into SSA also increased from 0.5 million Mg of milled rice in 1961 to

6.0 million Mg in 2003 and SSA currently accounts for 25% of global rice

imports, at a cost of more than US$1.5 billion per year. Therefore, many

African governments accord high priority to developing their local rice sector

as an important component of national food security, economic growth, and

poverty alleviation. The abundant supply of agroclimatically suitable

wetlands (�239 million ha) and water resources can support a large expan-

sion in rice area and productivity. Currently, less than 5% of the potentially

suitable wetlands are planted with rice because of various constraints.

Expansion and intensification of rice cultivation in SSA will not compete

with other crops in terms of land and water resources because, during the

rainy season, only rice can be grown on low‐lying wetlands, including inland

valleys. In addition, the labor‐intensive nature of rice cultivation will provide

additional sources of work and income to the rural poor, especially women.

Should labor shortages become acute, however, appropriate mechanization

can be considered. Small farmers want to earn money from rice farming, but

lack modern inputs and capital to fully exploit their rice lands as these items

are limited or not available. This is where an innovative public–private

partnership is desirable to support the intensification of rice farming.

Rice is cultivated in four ecosystems of SSA: dryland (38% of the

cultivated rice area), rainfed wetland (33%), deepwater and mangrove

swamps (9%), and irrigated wetland (20%). Many abiotic stresses (drought,

flood, and variable rainfall; extreme temperatures; salinity; acidity/alkalinity

and poor soils, soil erosion, and high P fixation) and biotic constraints

[weeds, blast, Rice yellow mottle virus (RYMV), and African rice gall

midge (AfRGM)] limit rice production on the continent. The changing

climate is expected to further aggravate the abiotic constraints and reduce

INCREASING RICE PRODUCTION IN SUB‐SAHARAN AFRICA 57

rice yields in all ecosystems. Rice production is also restricted by many

technical, management, socioeconomic, health, and policy constraints.

The constraints to irrigated wetland rice in the Sahel of SSA are similar to

those faced by Asian farmers in the 1960s; therefore, well ‐tested irrigated ricetechnologies from Asia and elsewhere are being introduced and adapted to

local conditions to obtain fast returns on investment. For rice in irrigated

wetlands in the humid and moist savanna zones, rainfed wetlands, and

drylands, locally developed NERICA (new rice for Africa) varieties and

production technologies are being tested in target environment s. The proge-

nies of Oryza glaberr ima and O. sativa subspecies indica are better adapted to

rainfed and irrigated wetlands, while those of O. glaberrima and O. sativa

subspecies japonica are more suited to rainfed drylands. In addition, research

is ongoing to tackle SSA‐ specific problems such as RYMV and AfRG M and

to develop e Ycient crop management technologies. Currently available best

management practices (integrated crop management options) for di Verentrice ecosys tems are shown in Table XV. Additional support through the

provision of technical advice through revamped national R&D services; a

supply of good‐quality seed and other inputs, including farm credit; and

enabling policy are needed for profitable and sustainable intensification of

rice cultivation in SSA. It is also critical to organize preventive health

measures for farmers against wetland‐related diseases (malaria, bilharzia,

and so on), protect certain natural wetlands (e.g., with bird sanctuaries),

preserve mangrove forests in strategic coastal belts and rich peats in inlands,

and use chemical inputs eYciently to minimize pollution and maintain

environmental quality while intensifying rice production. Anticipatory

research is needed to tackle the impacts of changing climate on rice farming

and the environment. Modern information and communication technologies

(ICTs) can be exploited to reach out to farmers in remote areas and to deploy

technologies eVectively. In addition, the development of innovative private–

public partnerships and the organization of farmers into user‐groups will

enhance the training, farmer education, and technology adoption required

for intensive commercial rice farming. # 2007, Elsevier Inc.

I. INTRODUCTION

Sub‐Saharan Africa (SSA) is the world’s poorest region. More than 30%

of the 900 million people living in SSA suVer from pernicious hunger and

malnutrition (Farm‐Africa, 2004; IAC, 2005; Rosegrant et al., 2005; Sanchez

and Swaminathan, 2005). The prevalence of diseases such as malaria and

AIDS is very high (FAO, 2006b) and many countries have been disrupted by

civil war. Although the current situation is grim, there is also much potential

to improve this situation.

More than 70% of the population of SSA is rural, and agricultural

development is essential to achieve economic growth, poverty alleviation,


and food security. The adoption of more productive agricultural practices

coupled with the development of rural infrastructure and local markets and

supportive agricultural policy is crucial to improving both rural and urban

living conditions. Achieving this requires that donor funds and a significant

part of national income be strategically invested in scientific agriculture and

farming methods and revamping national agricultural research and exten-

sion systems (NARES) as a means of improving rural livelihoods and

national food security.

African agriculture consists of a diverse set of farming systems that have

arisen in response to the large variations in ecological, social, and economic

conditions. Dixon et al. (2001) delineated 15 broad farming systems, includ-

ing forest‐based systems; systems dominated by livestock, cereals, and root

crops; and mixed systems. It is thus evident that improving the production of

several crops and livestock will have a role in agricultural development in

SSA. In this chapter, we focus on the role of a single crop, rice, that we think

will have a particularly important role in this process. From a low base, rice

consumption and production have increased tremendously in SSA over the

past decades, and this trend is expected to continue. Moreover, rice can be

very productive and sustainable and be produced in areas where other crops

cannot be grown. However, unlike in Asia, where the unique and uniform

rice‐based farming system benefited from Green Revolution technologies

during 1965–2000, productivity gains in African rice farming will come in

small increments due to Africa’s diverse nature of cropping systems. Yet the

potential for growth in the African rice sector is enormous.

In this chapter, we first assess the potential resources for rice production

and characterize the rice‐growing environments in SSA. We then discuss the

current status of rice farming and related production constraints in four

major ecosystems, assess the progress of rice research and development in

the past 20 years, and finally indicate the challenges and opportunities for

rice intensification in SSA.

II. RICE DEMAND AND SUPPLY

Rice is a traditional staple food in parts of West Africa and Madagascar,

and it is increasingly becoming an important food in East, Central, and

Southern Africa. In recent years, the relative growth in demand for rice is

faster in SSA than anywhere else in the world. Demand for rice has been

growing due to population growth and a shift in consumer preference for rice,

especially in urban areas. Annual per capita milled rice consumption in SSA

has increased from 11 kg in 1961 to 22 kg in 2003 (Fig. 1). Rice consumption

increased steadily in all countries, except Madagascar. Mean per capita

0

20

40

60

80

100

120

140

160

180

200

1966 1971 1976 1981 1986 1991 19961961 2001

Year

Mill

ed r

ice

con

sum

pti

on

(kg

per

cap

ita)

Côte d’Ivoire Kenya MadagascarNigeria Senegal South AfricaSub-Saharan Africa

Figure 1 Trends in per capita rice consumption in SSA, 1961–2001 (source: FAO‐STAT,

FAO, 2006a).


rice consumption is high in Madagascar (122 kg), Guinea Bissau (103 kg),

Cote d’Ivoire (Ivory Coast; 100 kg), Senegal (100 kg), Sierra Leone (93 kg),

the Gambia (90 kg), Guinea (73 kg), and Gabon (72 kg).

Local rice production cannot meet the increasing demand for rice in many

African countries (Hossain, 2006). Although milled rice production increased

from 2.2 million Mg in 1961 to 8.7 million Mg in 2004, rice imports also

increased from 0.5 million Mg in 1961 to 7.4 million Mg in 2004 (Fig. 2)

(FAO ‐STA T, FAO, 2006a ; IRRI, 2006). In 2002, fou r of the six largest rice

importers were Cote d’Ivoire, Nigeria, Senegal, and South Africa. Currently,

SSA accounts for 25% of global rice imports at a cost of more than US$1.5

billion per year. Projected rice imports intoWest Africa alone will be between

6.5 and 10.1 million Mg in 2020 (Lancon and Erenstein, 2002). Declining

global rice stocks and the predicted doubling of the rice price by 2008 will put

additional strains on rice‐importing countries in SSA. Therefore, national,

regional, and international agencies are now placing a high priority on devel-

oping the local rice sector in SSA as an important component of food security,

national economic growth, and poverty alleviation.

Rice is grown and consumed in 38 countries of SSA (Table I). Figure 3

shows the distribution of rice areas in SSA. Of the total of 8.46 million

hectares (ha) of harvested rice area in SSA (5.5% of the global rice area) in

2

4

6

8

10

12

0

14

1966 1971 1976 1981 1986 1991 19961961 2001

Pad

dy

rice

pro

du

ctio

n (

mill

ion

Mg

)

Year


0

1

2

3

4

5

6

7

8

1966 1971 1976 1981 1986 1991 19961961 2001

Year

Ric

e im

po

rt (

mill

ion

Mg

)


A

B

Figure 2 Local paddy rice (unmilled rice) production, 1961–2005 (A) and imports of milled

rice, 1961–2004 (B) into selected countries and SSA (source: FAO‐STAT, FAO, 2006a).


Table I

Harvested Rice Area, Percent of Irrigated Area, Production, and Yield of

Unmilled Rice (Paddy) in African Countries (2004)

Country Area (�103 ha)aFully/partially

irrigated (%)bProduction

(�103 Mg)aYield

(Mg ha�1)a

Angola 20.0 0 16.0 0.80

Benin 33.0 2 70.0 2.12

Burkina Faso 51.0 18 95.2 1.87

Burundi 19.5 21 64.5 3.31

Cameroon 20.0 95 62.0 3.10

Central African Republic 14.5 – 29.7 2.05

Chad 80.0 9 109.0 1.36

Comoros 14.0 – 17.0 1.21

Congo, DR 415.0 0 315.1 0.76

Congo Republic 2.0 0 1.5 0.75

Cote d’Ivoire 500.0 7 1150.0 2.30

Ethiopia 8.4 85 15.5 1.86

Gambia 16.0 7 22.0 1.38

Ghana 119.4 4 241.8 2.03

Guinea 525.0 10 900.0 1.71

Guinea Bissau 65.0 1 127.0 1.95

Kenya 11.0 100 50.0 4.55

Liberia 120.0 2 110.0 0.92

Madagascar 1222.7 52 3030.0 2.48

Malawi 30.0 28 49.7 1.66

Mali 451.0 22 877.0 1.94

Mauritania 17.0 100 77.0 4.53

Mauritiusc 0.0 0.0 0.0 0.0

Mozambique 179.0 2 201.0 1.12

Niger 27.8 80 76.5 2.75

Nigeria 3704.0 15 3542.0 0.96

Reunion 0.04 100 0.08 2.00

Rwanda 13.0 8 46.2 3.55

Senegal 95.0 50 264.5 2.78

Sierra Leone 210.0 – 265.0 1.26

Sudan 4.8 75 15.8 3.28

Swaziland 0.05 100 0.17 3.40

Tanzania 330.0 27 647.0 1.96

Togo 35.0 1 68.1 1.95

Uganda 93.0 2 140.0 1.51

Zambia 10.0 0 12.0 1.20

Zimbabwe 0.25 – 0.6 2.40

Total/mean for SSA 8459.4 19.8 12,714.0 1.50

aSource of basic data: FAO‐STAT (FAO, 2006a).bBest estimates from data (1995–2004) obtained from FAO‐Aquastat (2005) at www.fao.org/

WAICENT/FAOINFO/AGRICULT/AGL/aglw/aquastat/countries/index.stm (accessed May

10, 2006) and FAO‐CORIFA (2005).cMauritius has a few hectares of rice now; however, it plans to replace some sugarcane fields

with irrigated rice in coming years to reduce rice imports.


http://www.fao.org/WAICENT/FAOINFO/AGRICULT/AGL/aglw/aquastat/countries/index.stm


Each dotrepresents 2500 ha

15�

0�

0� 15� 30� 45� 60�

0 1000

(km)

−15�

−15�

−30�

30�

Figure 3 Distribution of rice areas in SSA.


2004, Nigeria and Madagascar accounted for 60% of the rice land; nine

countries cultivated rice on more than 100,000 ha each; four countries grew

rice on 50,000–100,000 ha each; and others were small rice producers with

less than 50,000 ha each (Table I). All these countries together produced

only 3% of the global rough rice output of more than 600 million Mg

per annum. In 2004, rice yields varied from 0.76 Mg ha�1 in Congo DR to

4.53–4.55Mg ha�1 inMauritania and Kenya, with an average of 1.50Mg ha�1

for the whole of SSA (FAO, 2006a).

In 1960–2000, rice area increased in SSA, but rice yields stagnated at a low

level or decreased (Fig. 4). From 2000 to 2005, average rice yields continued to

decline in West Africa and Nigeria, and increased only slightly in East Africa

and Madagascar. Therefore, any increase in national rice production came

from an expansion in area rather than a substantial increase in productivity.

This is a disturbing trend given the escalating demand for rice in many

SSA countries.

10

8

6

4

2

0

Ric

e ar

ea (

mill

ion

ha)

Ric

e yi

eld

(Mg

ha−1

)

Sub-Saharan Africa

Western Africa

Eastern Africa

Madagascar

Nigeria

Sub-Saharan Africa

Western Africa

Eastern Africa

Madagascar

Nigeria

Year1960 1970 1980 1990 2000

1960 1970 1980 1990 2000

2.5

2.0

1.5

1.0

0.5

Year

Figure 4 Trends in rice area and yield in Nigeria, Madagascar, West Africa, East Africa, and

SSA, 1960–2005 (source: FAO‐STAT, FAO, 2006a).


III. WETLANDS: THE POTENTIAL RESOURCE FORRICE PRODUCTION IN SSA

The rice plant is adapted to growing in swampy conditions and is sensitive

to water stress. This makes wetlands the most suited areas for rice cultiva-

tion. The types and distribution of wetlands and their potential for rice

cultivation in SSA are discussed in this section.


A. DEFINITION, AREA, AND DISTRIBUTION OF WETLANDS

For the purpose of agricultural land‐use planning, wetlands can be defined

as areas subject to periods of completely water‐saturated soils with possibi-

lities of flooding during part of the crop‐growing period. The depth and

duration of flooding of these soils depend on the position of the land on the

catena and the extent of drainage available; the flooding may be for part of

the growing season or throughout the year.

Wetlands are found not only in low‐lying areas (river and coastal flood-

plains, deltas, and depressions) but also on upper river terraces, foot slopes,

and hilltops. For example, in West and Central Africa, wetlands are a part of

the inland valley system, which is a continuum of drylands on upper and

mid‐slopes and wetlands in valley bottoms. On lower slopes, the boundary

between wetland and dryland is often gradual. The distribution of normal

and salt‐aVected (saline) wetlands along with major rivers and lakes in SSA

is shown in Fig. 5.

Our discussion on area, types and characteristics, and distribution of wet-

lands in SSA is derived from Andriesse (1986). On the basis of the 1:5 million

soil map of FAO (1977), the estimated wetland area in SSA is 239 million ha

(Table II) (Andriesse, 1986). About 40% of the total wetland area is found

in the equatorial region and the rest in the Guinea savannas (Fig. 5). About

36 million ha of wetlands are located in the tropical highlands of East and

Central Africa and Madagascar. These estimates of wetland area must be

used cautiously because of the possible large margins of error in estimates

derived from small‐scale maps.

B. TYPES AND CHARACTERISTICS OF WETLANDS

Wetlands in SSA are grouped into four categories: inland basins and

drainage depressions, inland valleys, river floodplains, and coastal wetlands.

A brief description of each category is given below.

1. Inland Basins

Inland basins are the largest area of wetlands potentially suitable for rice

cultivation, they occupy 108 million ha (45% of the total wetland area in

SSA) (Table II). They comprise drainage depressions and inland deltas

of rivers, with imperfectly to poorly drained and potentially acidic soils

(Ultisols, Oxisols, Alfisols, Entisols, and Vertisols). Examples are the Upper

Nile, Sokoto, Lake Chad, and Congo basins; the shallow swamps around

Lake Bangweulu and the Kafue flats; and the lacustrine deposits of Lake

Rukwa and Lake Eyasi.

30�

15�

0�

Wetlands

Saline wetlands

Rivers and lakes

30� 45� 60�

0 1000

(km)

−15�

−15� 0� 15�

−30�

Figure 5 Distribution of normal and saline wetlands along with major rivers and lakes in

SSA.

Table II

Estimated Areas of Four Types of Wetlands in SSAa

Type of wetlands Area (million ha)

Percentage of

total wetlands

Percentage of

total area

Inland basins/depressions 107.5 45 9.0

Inland valleys 85.0 36 7.0

River floodplains 30.0 12 2.5

Coastal wetlands 16.5 7 1.5

Total 239.0 100 20.0

aAdapted from Andriesse (1986).



2. Inland Valleys

Inland valley wetlands occupy �85 million ha (36% of the total wetland

area in SSA) (Table II); only 10–15% of the inland valley area is used for

agriculture. Narrow inland valleys are located upstream from river flood-

plains that are much wider. Each inland valley represents a toposequence of

a valley bottom with its hydromorphic edges, and the contiguous dryland

slopes and crests that contribute runoV and seepage to the valley bottom.

They are known as dambos or boliland in eastern and central Africa, fadamas

in northern Nigeria and Chad, bas‐fonds or marigots in francophone Africa,

and inland valley swamps in Sierra Leone. Most inland valley wetlands are

concentrated in the intertropical zone where rainfall is superior to 700 mm,

and their catchment sizes generally range from 100 to 2000 ha. The soils

(Entisols) in the valley bottoms are flooded during the rainy season, whereas

the soils (Ultisols, Oxisols, Alfisols, and Inceptisols) on adjacent drylands

are aerobic and erosion‐prone.

3. River Floodplains

An estimated area of 30 million ha (12% of the total wetland area) is under

river floodplains in SSA (Table II). A floodplain is awide, flat plain of alluvium

bordering streams and rivers that flood it periodically. Well‐developed flood-

plains extend from tens of meters to tens of kilometers on either side of

large rivers such as the Gambia, Niger, Benue, Zaire, Zambezi, Limpopo,

Tana, White and Blue Nile, and Chari. Soils of the floodplains (Entisols,

Inceptisols) are moderately well to poorly drained and medium‐ to fine‐textured with moderate to high fertility. Soils can be saline and/or alkaline

in drier regions.

4. Coastal Wetlands

Coastal wetlands cover an estimated area of 16.5 million ha (7% of the

total wetland area in SSA) (Table II). They comprise

� Deltas (e.g., Niger in Nigeria, Rufiji in Tanzania, and Zambezi in

Mozambique)

� Estuaries (at the mouths of the Zaire, Cross, Gambia, and Corubal rivers)

� Intertidal flats or lagoons along the West and East African coasts.

Soils (Entisols, Inceptisols, Histosols) are poorly drained and nonsaline in

freshwater swamps, acid sulfate (Entisols, Inceptisols) in mangrove swamps,


poorly drained and saline (Inceptisols) in lagoons, coarse‐textured (Entisols,

Inceptisols) in sand bars and dunes, and organic (Histosols) in permanently

flooded areas.

IV. RICE SOIL RESOURCES

Soils provide the base for crop production. The physical and chemical

characteristics of soils reflect the parent materials from which they are

derived. For example, coarse infertile soils are developed from poor and

acid rocks (sandstones, granites, quartzites, rhyolites), coarse‐ to medium‐textured soils of low to moderate fertility from intermediate rocks (horn-

blende, granites, quartz‐feldspar gneisses, diorites, andesites), and medium

to fine, relatively fertile soils from rich parent rocks (amphibolites, dolerites,

basalts, hornblende gneisses, shales, siltstones). Soils derived from volcanic

ash are rich in most nutrients except N and P. In addition, the climate, the

extent of weathering, the position of soils on landscape, vegetation cover,

and soil moisture regimes aVect the physical, chemical, and biological prop-

erties of soils. In this section, we briefly discuss the two broad categories of

soils—dryland and wetland—and their characteristics.

A. DRYLAND SOILS AND THEIR CHARACTERISTICS

Dryland soils on the upper and middle slopes of the catena are generally

well drained, deep to very deep, and coarse‐ to medium‐textured or gravelly

in the humid forest and Guinea savanna zones. Soils in the upper parts of the

toposequence are moderately to well drained, shallow to medium in depth,

and coarse‐ to medium‐textured or gravelly in the Sudan savanna transition

zones (Andriesse and Fresco, 1991). Most of the dryland soils are highly

weathered and greatly leached with low‐activity clays (silicious, kaolinitic,

and halloysitic minerals) in the humid zones and less leached and fairly rich

in weatherable minerals in the Sudan savanna transition zones.

The red clayey or clay‐loam soils dominant in the humid forest andGuinea

savanna zones are classified as Ultisols and Oxisols, and some as Alfisols; the

brown sandy or sandy loam soils of the Sudan savanna transition zones

belong to Alfisols, Inceptisols, or Entisols; and the organic matter (OM)‐rich, relatively fertile soils of the highlands of East and Central Africa and

Madagascar are mostly Inceptisols. Volcanic ash soils found in some dryland

rice areas (e.g., in parts of Cameroon) are also Inceptisols (Kawaguchi and

Kyuma, 1977; Sanchez and Buol, 1985). Gravelly soils (Entisols) and soils on

steep slopes are highly prone to erosion and not suitable for dryland rice.


The inherent fertility of most dryland soils is low (low pH, cation

exchange capacity, and base saturation) in warm and humid zones due to

intense weathering of parent materials, and medium to high in semiarid

zones due to less intense weathering and, in West Africa, due to deposition

of Ca, Mg, and K from dust deposits from the Sahara Desert that occur

in the dry season (DS) (Andriesse and Fresco, 1991). Subsoil acidity and Al

and Mn toxicity are common problems in some soils. Soil OM and N

contents decrease as we move from humid to subhumid to semiarid zones.

Total soil P is generally low, with only 2–4% of the total P available to plants

(Table III) (Breman, 1998). This is because of the high P‐fixing capacity of fine‐textured soils found in humid and subhumid zones (Abekoe and Sahrawat,

2001; Juo and Fox, 1977). Therefore, P fertilization is an important requisite

to get a crop response to other nutrients such as N. K deficiency is more

severe in humid regions than in drier areas.

B. WETLAND SOILS AND THEIR CHARACTERISTICS

Rice soils converted from natural wetlands are fairly rich in exchangeable

bases (Ca, Mg, and K), slightly acidic to neutral (pH 6–7), low in P‐fixationcapacity, and not Al toxic. The soils are often mineral in seasonally dry

wetlands and peaty in permanently flooded wetlands. Most mineral wetland

soils are fluvial, lacustrine, estuarine, or marine alluvial materials. In soil

taxonomy (Soil Survey StaV, 1998), soils with an aquic moisture regime and

specified morphologic characteristics of wetness are distinguished at the

suborder level (e.g., Inceptisols: Aquepts; Alfisols: Aqualfs). At the subgroup

level, aquic subgroups with signs of wetness only in lower horizons are not

considered as wetland soils, except the aquic subgroups of flooded Vertisols,

Table III

Mean Chemical Characteristics of Dryland Soils (0–0.3 m) in Four

Agroecological Zones of West Africa

Soil properties Equatorial forest Guinea savanna Sudan savanna Sahel

pH (water) 5.7 5.7 6.7 5.7

Org. C (g kg�1) 20 12 6 3

Total N (g kg�1) 2.0 1.3 0.5 0.2

Total P (mg kg�1) 260 340 210 100

Bray‐1 P (mg kg�1) 9 7 4 4

CECa (cmol kg�1) 8.7 8.5 8.1 2.5

Base saturation (%) 28 59 69 28

aCEC, cation exchange capacity.

Adapted from Breman (1998).


such as Chromoxererts, Chromuderts, Pelloxererts, and Pelluderts, with

distinct mottles in the upper 0.5 m of the soil profile. Histosols are mostly

wetland soils. In another classification of soils, the FAO–UNESCO legend for

the soil map of the world (FAO, 1977), the Gleysol, Fluvisol, Planosol, and

Histosol and gleyic units of Acrisol, Arenosol, Cambisol, Luvisol, Podsol,

and Regosol and periodically wet Ferralsol refer to wetland soils. Major

wetland rice soils of SSA, their classification in soil taxonomy and the

FAO–UNESCO system, and a third system based on fertility capability

classification (FCC) and their potential for rice cultivation are given in

Table IV. The FCC (Buol et al., 1975) is a technical system for grouping

soils according to the kinds of problems they present in agronomic manage-

ment of crops. It is based on quantitative topsoil and subsoil (up to 0.5 m)

parameters directly relevant to plant growth. Additional locally important

features can be considered and added to the FCC as primes (0) or asterisks (�).The adapted FCC of wetland soils (Sanchez and Buol, 1985) is used for the

FCC in Table IV.

Rice soils from converted natural wetlands include alluvial (Entisols),

hydromorphic (Inceptisols), black cracking clay (Vertisols), and red clayey

(Ultisols and Oxisols) or loamy soils (Oxisols or Alfisols). Except for the

black clay soils, they are acidic, moderately to highly P‐fixing (Abekoe and

Sahrawat, 2001), and low in potentiality, with less than 10% weatherable

minerals; they are also diYcult to puddle. These soils scattered all over SSA

are moderately to highly suitable for rice cultivation (Table IV).

Organic soils (OM> 20%) orHistosols include peat andmuck soils found in

continuously flooded wetlands in low‐ and high‐altitude regions (forest zonesof West Africa and highlands of East and Central Africa and Madagascar).

There are two classes of organic soils: deep (organic in top 0.5m of the profile)

and shallow organic over (clay, loamy, or sandy) mineral soils within the

top 0.2 m of the profile. Shallow organic soils over clay are the most common

in SSA and elsewhere, and they are low in bearing capacity (mechanization

not possible) and deficient in many nutrients (Sanchez and Buol, 1985).

Acid sulfate soils are organic soils over clay with marine sediments found in

some coastal wetlands of SSA.

Many soils with adequate water retention capacity but lacking an aquic

soil moisture regime are converted into artificial (or anthropic) wetlands

through terracing and irrigation. Two important soil types of artificial wet-

lands are oxic soils (Oxisols, OxicUltisols/Alfisols) andAndepts (volcanic ash

soils). Oxic soils have more than 35% clay, low pH and cation exchange

capacity, high levels of free iron that can result in Fe toxicity when flooded,

and high P‐fixing capacity and Al toxicity (Abekoe and Sahrawat, 2001;

Sahrawat, 2004a); they are generally diYcult to puddle and have low to

moderate potential for rice cultivation (Sanchez and Buol, 1985). These

soils are found in rainforest and derived savanna zones. Volcanic ash soils

Table IV

Wetland Rice Soils, Their Classification, and Their Potential for Rice Production in Africa

Soil type

Soil Survey StaV

(1998)

FAO–UNESCO Soil

Map (FAO, 1977) FCCa

Potential for

rice cropping

A. Wetland rice soils converted from natural wetlands

Young alluvial

soils

Entisols:

Ustifluvents,

Torrifluvents,

Xerofluvents,

Ustipsamments

Fluvisols: Dystric,

Eutric

SLgek, SCghek High

Arenosols: Gleyic

Black or peaty

soils

Inceptisols:

Epiaquepts,

Humaquepts

Gleysols: Humic Lgak (coastal),

Cgaik (highlands)

Moderate

Hydromorphic

Vertisols

Vertisols:

Calciaquerts,

Duraquerts,

Dystruderts,

Calcixererts,

Durixererts

Vertisols: Pellic Cvg High

Inceptisols:

Epiaquepts

Red clay soils:

humid zone

Ultisols: Udults,

Aquults

Acrisols: Ferric,

Gleyic

Cgaeik0 Moderate

to low

Red clay‐loamsoils:

subhumid and

semiarid zones

Oxisols: Aquox,

Ustox

Ferralsols: Orthic,

humic

(LC)ghk0d,Lgh(e)k

Moderate

Alfisols: Aqualfs,

Udalfs, Ustalfs

Luvisols: Orthic,

Ferric

B. Wetland rice soils in anthropic (artificial) wetlands on terraced landscapes

Oxic soils

(>35% clay)

Oxisols, Oxic

Ultisols/Alfisols

Ferralsols, Acrisols,

Luvisols

Cigae Low/

moderate

Tropical brown

soils/volcanic

ash soils

Inceptisols:

Epiaquepts,

Sulfaquepts,

Halaquepts

Cambisols: Gleyic,

Eutric

Andosols: Ochric,

Humic

Lxd, Lxg High/very

high

Entisols:

Hydraquents

C. Problem soils

Acid sulfate soils Entisols:

Sulfaquents

Fluvisols: Thionic OCcg�ak Low/

moderate

Inceptisols:

Sulfaquepts

Peats (deep) Histosols (>20%

organic matter)

Histosols: (>20%

organic matter)

Og�akk0 Low/very low

Peats (shallow) OCg�akk0,OLg�akk0,OSg�akk0

Low/

moderate

Saline soils Inceptisols:

Epiaquepts,

Aridisols:

Natrargids

Solonchaks: Gleyic Ssgbkk0, SCsgbkk0 Limited


Table IV (continued)

Soil type

Soil Survey StaV

(1998)

FAO–UNESCO Soil

Map (FAO, 1977) FCCa

Potential for

rice cropping

Alkaline soils Inceptisols:

Natraquepts

Solonets: Gleyic Cngbgkk0,SCngbkk0

Limited

Alfisols: Natraqualfs

Vertisols:

Natraquerts

Degraded gray

soils

Ultisols:

Plinthaquults

Acrisols: Plinthic SLgkk0ea,CLgkea

Moderate

(H2S

toxicity)

Skeletal soils

(>35% gravel)

Ultisols:

Endoaquults

Planosols: Eutric,

Dystric

SL00gkk0i, LC00gkk0i,SRgk, LRgk

Very low

aFCC, fertility capability classification (Sanchez and Buol, 1985): S, sand; C, clay; L, loam;

O, organic; R, rocky; c, acid sulfate; x, X‐ray amorphous allophonic; g, gleic; g�, pergleic;gd, wetland soils dry for 60 days or more; k, low potential productivity with <10% weatherable

minerals; k0, low in K; e, low cation exchange and buVering capacity; a, acid pH < 5 þ Al toxic

þ P‐fixing; h, acid, pH 5–6 but not Al toxic; b, basic pH > 7.3; v, vertic; s, saline; n, alkaline;

%, steep slope; i, high levels of free iron, highly P‐fixing.Note: FCC ratings for diVerent soils are first approximations based on available information,

and they can be modified or further improved with additional data at local level.


(Inceptisols) are dominant in X‐ray amorphous allophoneminerals, rich in all

nutrients except N and P, and high in P‐fixation capacity; they pose moderate

diYculty to puddling and regenerate the structure easily on drying. They are

good for rice dryland crop rotations with high productivity (Kawaguchi and

Kyuma, 1977).

DiVerent types of problem soils occur in SSA: acid sulfate soils (Inceptisols:

Sulfaquepts) in mangrove swamps, deep and shallow peats (Histosols) in low‐and high‐altitude areas, saline (Inceptisols: Halaquepts) and alkaline (Incep-

tisols: Natraquepts; Vertisols: Natraquerts) soils in the Sahel and coastal

wetlands, degraded soils (Ultisols: Aquults) in the humid forest zones, and

skeletal soils (Ultisols: Aquults) on adjacent sloping drylands of inland

valleys. Soil pH decreases drastically and Al toxicity increases only when

acid sulfate soils are drained. Remediation of adverse conditions and the

combined use of salt‐tolerant rice varieties and integrated nutrient applicationare needed to grow rice on saline and alkaline soils.

V. AGROCLIMATIC ZONES AND RICE ECOSYSTEMS

The suitability of land for various crops is determined by climate and

weather variables (agroclimatic zones), landscape moisture regimes (physio‐hydrographic positions), and soil characteristics. Rice thrives in areas with


warm temperatures (above 20�C during the cropping season), annual rain-

fall ranging from 0.5 to >1.5 m, and growing periods of 90þ days. Rainfall

distribution is generally monomodal with a distinct humid period in areas

with a rainfall range of 500–1000 mm per annum (e.g., northern and south-

ern Guinea savanna zones) and bimodal with two growing seasons toward

the equator (Andriesse, 1986).

The classification of land and water resources into (agro)ecosystems is

helpful for the planning, development, management, and monitoring of

these resources. The choice of classification scheme is always subjective to

some extent and will depend on the purpose of classification. Andriesse and

Fresco (1991) defined 18 rice environments by combining six landscape or

physio‐hydrographic positions with three agroecological zones (AEZs) for

West and Central Africa. For this chapter, we use surface‐water regimes to

define four major rice ecosystems: dryland, rainfed wetland, deepwater and

mangrove swamps, and irrigated wetland (Fig. 6). The distribution of rice

areas into four ecosystems and the related environmental/human disease

constraints for diVerent African countries are shown in Table V. For 16

large rice‐growing countries, actual mean rice areas (1995–2004) in diVerentecosystems are provided in Table VI.

A. DRYLAND RICE ECOSYSTEMS

Dryland rice is also known as ‘‘upland’’ or ‘‘pluvial’’ rice. It is cultivated

on level or sloping lands and on hydromorphic fringes (Fig. 6) in fields that

do not have bunds to retain surface water (Sie, 1991). Flooding is rare in this

ecosystem, and dryland rice depends solely on rainfall and should have a

water table that remains at 0.5 m or more below the soil surface. Similar to

Plateau

Slopes

Valley bottom FloodplainsHydromorphic edge

Rainfed wetlandIrrigated wetland

Dryland

DW/Mangrove

Figure 6 Major rice ecosystems of SSA as defined by surface‐water regimes.

Table V

Rice Area by Ecology/Ecosystem and Related Environmental and Human Disease Problems

for Countries of SSA

Country

Mean area

(1995–2004)

(�103 ha)a

Percentage of area by

ecology/ecosystema

Environmental and human

disease problemsIRb RWRc DRd DWRþe

Angola 21.2 0 100 0 0 HIV, malaria, cholera

Benin 21.7 2 7 91 – Malaria

Burkina Faso 47.9 46 50 4 0 Bacteria/N/Cl�1

pollution, salinity

Burundi 17.7 21 74 4 0 Malaria, bilharzia

Cameroon 16.9 95 5 0 0 Malaria, bilharzia

Central Africa

Republic

13.1 0 3 97 0 Malaria

Chad 83.7 9 6 0 85 Poor water and sanitation

Comoros 14.0 – – – – Malaria/diarrhea/dengue

Congo, DR 445.2 0 11 89 0 Petroleum, mineral

pollution

Congo Republic 1.8 0 100 0 0 –

Cote d’Ivoire 500.9 7 15 78 0 Malaria/worms

Ethiopia

(2001–2004)

8.4 85 15 0 0 Salinity, malaria

Gabon 0.5 100 0 0 0 –

Gambia 13.9 7 63 16 14 Salinity, deforestation

Ghana 116.9 24 21 55 0 Water pollution, malaria

Guinea 495.5 10 23 44 23 Malaria/diarrhea/bacterial

diseases

Guinea Bissau 65.5 1 27 27 45 Salinity/silting,

malaria/diarrhea

Kenya 11.8 100 0 0 0 Land/wildlife park

conflicts, malaria

Liberia 121.0 2 6 92 0 –

Madagascar 1195.7 52 18 29 1 Malaria, bilharzia

Malawi 43.8 28 72 0 0 Malaria

Mali 365.3 22 13 1 64 Bilharzia

Mauritania 18.1 100 0 0 0 Salinity, soil degrading

Mauritius 0 0 0 0 0 –

Mozambique 164.6 2 59 39 0 Salinity, HIV/malaria/

diarrhea/bilharzia

Niger 22.7 80 0 0 20 Malaria/diarrhea/bilharzia

Nigeria 2466.4 17 47 30 6 Pollution, malaria/worms

Reunion 0.04 100 0 0 0 –

Rwanda 5.1 8 92 0 0 Deforestation/soil erosion/

peat drying

Senegal 79.2 50 40 0 10 Acid/alkalinity/pollution

Sierra Leone 236.6 0 28 68 4 Deforestation/peat harvest

Sudan 4.7 75 – – – Silting/pollution

(continued)


Table V (continued)

Country

Mean area

(1995–2004)

(�103 ha)a

Percentage of area by

ecology/ecosystema

Environmental and human

disease problemsIRb RWRc DRd DWRþe

Swaziland 0.05 100 0 0 0 Malaria, bilharzia

Tanzania 439.9 4 73 23 0 Salinity/pollution/silting

Togo 38.1 1 19 80 0 Pollution, malaria

Uganda 71.0 2 53 45 0 Salinity/silting, malaria

Zambia 10.9 0 100 0 0 Malaria/diarrhea

Zimbabwe 0.2 – – – – Civil strife, malaria/

bilharzia/diarrhea/

agrochemical poisoning

Total/mean for

SSA

7180.0 19.8 33.5 37.8 8.9 –

aBest estimates from data (1995–2004) obtained from FAO‐Aquastat (2005) at www.fao.org/


10, 2006), FAO‐CORIFA (2005), Defoer et al. (2002), Adegbola and Singbo (2005), and

Ezedinma (2005).bIR, irrigated wetland rice.cRWR, rainfed wetland rice.dDR, dryland rice.eDWRþ, deepwater and mangrove rice.


the situation in Asia, dryland rice is generally a subsistence crop in Africa.

It is of critical importance for the local food security of poor communities

that do not have access to wetland fields. In Cote d’Ivoire, Guinea, Guinea

Bissau, and Sierra Leone, dryland rice is the only staple available between

the maize and cassava harvests or between sweet potato and cassava

(McLean et al., 2002). In the Zambezi region of Mozambique, dryland rice

is the main source of food for the poor.

1. Dryland Rice Area

Of the global dryland rice area of 14 million ha in the 1990s, 2.7 million ha

are planted to dryland rice in Africa (Table III); it accounts for an estimated

38% of the total rice area in SSA. Nearly 97% of the cultivated rice area

in the Central African Republic is in drylands. Other countries with domi-

nant dryland rice ecosystems (more than 65% of the cultivated rice area) are

Liberia, Benin, Congo DR, Togo, Cote d’Ivoire, and Sierra Leone (Table V).

Countries with more than 100,000 ha of dryland rice are Congo DR, Guinea,



Table VI

SSA Countries with Large Areas in Rice Ecologies/Ecosystems (Mean of 1995–2004)

Country

1995–2004 Mean rice area (�103 ha)a

IRb RWRc DRd DWRþe Total

Benin 0.4 1.5 19.8 0.0 21.7

Burkina Faso 22.0 24.0 1.9 0.0 47.9

Chad 7.5 5.0 0.0 71.2 83.7

Congo, DR 0.0 49.0 396.2 0.0 445.2

Cote d’Ivoire 35.1 75.1 390.7 0.0 500.9

Ghana 28.1 24.5 64.3 0.0 116.9

Guinea 49.5 114.0 218.0 114.0 495.5

Liberia 2.4 7.3 111.3 0.0 121.0

Madagascar 621.8 215.2 346.8 12.0 1195.7

Mali 80.4 47.5 3.6 233.8 365.3

Mozambique 3.3 97.1 64.2 0.0 164.6

Nigeria 419.3 1159.2 739.9 148.0 2466.4

Senegal 39.6 31.7 0.0 7.9 79.2

Sierra Leone 0.0 66.2 160.9 9.5 236.6

Tanzania 17.6 321.1 101.2 0.0 439.9

Togo 0.4 7.2 30.5 0.0 38.1

Uganda 1.4 37.6 32.0 0.0 71.0

aBest estimates from data (1995–2004) obtained from FAO‐Aquastat (2005) at www.fao.org/


10, 2006), FAO‐CORIFA (2005), and FAO‐STAT (FAO, 2006a).bIR, irrigated wetland rice.cRWR, rainfed wetland rice.dDR, dryland rice.eDWRþ, deepwater and mangrove rice.


Cote d’Ivoire, Liberia, Madagascar, Nigeria, Sierra Leone, and Tanzania

(Table VI).

2. Cropping Systems

Dryland rice systems range from shifting to permanent cultivation. Shift-

ing or slash‐and‐burn cultivation is common in humid forest zones of West

Africa where farmers cut and burn the bush‐fallow vegetation and plant rice

as the first crop to exploit the soil fertility built up during the fallow period

and the ash from burning. They may apply a little manure or compost, but

no chemical fertilizers are used. As this practice depletes the soil, weeds build

up and rice yields decline drastically after the second crop, when farmers

plant cassava on old plots and move to a new area for rice cultivation.




Nutrient mining degrades the soil in this type of slash‐and‐burn system

(Fernandez et al., 2000; Oldeman et al., 1991).

Farmers plant rice as a sole crop or mixed with maize, beans, yam,

cassava, or plantains (mixed cropping) to avoid risks. In areas with a long

growing season and suYcient rainfall, dryland rice is rotated with maize,

cowpea, beans, soybean, or sweet potato. In inland valleys, dryland rice and

cash crops are often grown on hydromorphic fringes while fodder crops and

trees grow on upper slopes and crests. In the highlands of East Africa,

dryland rice is rotated with wheat, maize, potato, or sweet potato.

3. Cultivation Practices and Yields

In this ecosystem, the fields are not bunded, there is no flooding, and the

soil remains aerobic (not saturated with water) for most of the growing

season. Rice seeds are sown by broadcasting or dibbling in hand‐hoed fields.

An adequate supply of soil water is critical for good plant growth and yield.

This can be achieved by in situ rainwater harvesting (RWH) through im-

proved infiltration of rainwater by proper tillage, reduced water loss from the

soil surface by proper mulching or plant cover, and improved crop‐water useby selecting adapted varieties and following moisture‐conserving cultivation

practices (Hatibu et al., 2000). As dryland rice farmers are generally poor,

they may apply some household wastes and other organic manure but do not

generally apply purchased inputs to their rice crops. At harvest time, mature

panicles are collected, dried, and threshed manually.

Dryland rice yields range from less than 0.5 Mg ha�1 on subsistence farms

to 2 Mg ha�1 in well‐managed permanent cropping of rice in rotation with

legumes and other crops. Yields are low on subsistence farms because of poor

cultivation methods, low‐input use, excessive weeds, and depleted soils. With

the introduction of dryland NERICA varieties in SSA, farmers in Uganda

obtained average rice yields of 2.2 Mg ha�1 with moderate inputs (Kijima

et al., 2006).

4. Production Constraints

Both abiotic and biotic constraints limit rice production in drylands.

Serious abiotic constraints include variable rainfall, low temperature in

high‐altitude areas, and poor soils. The total rainfall of 0.9–2.0 m is ade-

quate in the humid and subhumid areas where dryland rice is generally

grown in SSA, but the rainfall distribution can be poor, with unpredictable

dry spells. On the other hand, the temperature during the growing season is


relatively favorable in most parts, except in the tropical highlands of East

and Central Africa and Madagascar.

Degradation of soil structure and surface sealing constrain crop emergence

and growth in semiarid areas (Andriesse and Fresco, 1991). Dryland rice

requires extensive weeding to get a decent yield and, in such systems, topsoil

erosion can be a serious problem, especially on slopes. Drought is another

serious problem for dryland rice due to the inadequate quantity and/or poor

distribution of rainfall and shallow depth of and surface crusting in some soils.

Among biotic factors, weeds are the most serious, followed by blast and

brown spot diseases. Weeds are generally more competitive than rice in

infertile dryland soils. Striga is a parasitic weed of dryland cereals, including

rice. Estimated yield losses due to weeds range from 30 to 100%. Weed

infestation and loss of N reduce yields by 25% on intensive dryland rice

farms of West Africa (Becker and Johnson, 2001). Stem borers and rice bugs

are the major insect pests. Nematodes are serious problems in continuously

monocropped dryland rice fields (Coyne et al., 2004; Plowright and Hunt,

1994) and can reduce yields by up to 30%. Termites are problems in some

areas. Rodents and birds damage rice crops in all ecosystems.

B. WETLAND RICE ECOSYSTEMS

Unlike the dryland ecosystem, rice fields in the wetland ecosystem are

flooded during the growing season. We distinguish three types of wetland

rice ecosystems—rainfed wetland, deepwater, and irrigated—as determined

by the surface‐water regime. The ecosystem is considered to be rainfed

wetland when the water supply to crops is from rainfall and groundwater.

In contrast, in the deepwater ecosystem, most of the water on the fields is from

the lateral flow of water onto the land. In the irrigated wetland ecosystem, a

significant part of the water supply is from irrigation.

1. Rainfed Wetland Rice Ecosystem

Rainfed wetland rice is grown on lower parts of the toposequence and in

valley bottoms (Fig. 6) in level to slightly sloping bunded fields that are

flooded by rainwater for a part of the growing season to water depths that

may exceed 1.0 m for not more than 10 consecutive days. Both rainwater

and stored groundwater support rainfed wetland rice. Four types of flooded

wetlands are recognized in Africa: riverine shallow, riverine deep, boli-

land (grassy inland swamps), and mangrove (Andriesse and Fresco, 1991;

Buddenhagen, 1986).


Rainfed wetlands are characterized by a lack of water control, with

droughts and floods being potential problems (Hatibu et al., 2000; McLean

et al., 2002). On the basis of the constraints, rainfed wetlands can be divided

into four subecosystems: (1) favorable, (2) drought‐prone, (3) submergence‐prone, and (4) drought‐ and submergence‐prone. All four subecosystems

occur in SSA. Most inland valley bottoms represent the favorable rainfed

wetlands which could be the next frontier for intensification of rice and rice‐based cropping systems. Rice varieties and production technologies devel-

oped for the irrigated ecology can be easily adapted for rice in favorable

rainfed wetlands. Other rainfed wetland (drought‐, flood‐, and drought‐ andflood‐prone) subecosystems are found in riverine shallow, riverine deep,

hydromorphic edges of inland valleys, and mangrove ecologies. They are

highly diverse, with often variable rainfall patterns, adverse soils, and many

abiotic and biotic constraints. In addition, farmers are poor and have to

adapt their cropping practices to the complex risks, potentials, and problems

characteristic of such ecosystems.

a. Rainfed Wetland Rice Area. Of the global rainfed wetland rice area

of 54 million ha, an estimated 2.4 million ha are found in SSA; this is equal to

an estimated 33% of the total rice area in SSA (Table V). The rainfed wetland

rice ecosystem is generally found in the humid and subhumid forest andmoist

savanna zones of SSA. During 1995–2004, Nigeria had the largest area under

rainfed wetland rice (1,159,208 ha), followed by Tanzania (321,127 ha),

Madagascar (215,226 ha), Guinea (113,965 ha), Mozambique (97,114 ha),

Cote d’Ivoire (75,135 ha), and Sierra Leone (66,248 ha) (Table VI).

b. Cropping Systems. The number and choice of rice and other crops

to grow on rainfed wetlands depend on the length of the rainy season and

water availability. Farmers generally grow one crop of rice during the wet

season (WS) and leave the land fallow for the rest of the year. Vegetables,

sweet potato, or taro may be grown on mounds or bunds adjacent to flooded

rice fields (Andriesse and Fresco, 1991). If the rains extend to 5 months or

more, farmers can grow a post‐rice crop such as corn, soybean, vegetables,

or wheat (in highlands). Beans, cowpea, and vegetables are grown with

residual moisture in many inland valley bottoms and swamps of West Africa

(WARDA, 2002).

c. Cultivation Practices and Yields. Farmers sow seeds by broadcasting

on plowed land and fields are bunded to collect rainwater. They weed,

redistribute seedlings to ensure uniform crop stand, and harvest by hand,

but they add few or no purchased inputs (fertilizers or biocides). Harvested

rice is threshed on dry ground in the field or near the house. Rice is dehusked

by hand pounding in a mortar or by small village mills. Rice is stored in


large baskets for home consumption or in community warehouses for sale.

In West Africa, rice husks are mixed with clay and used for plastering house

walls or for making mud bricks (Murray, 2005).

Small farmers often plant traditional rice varieties and apply very few

external inputs. As a result, they obtain yields from 1 to 2 Mg ha�1 in SSA

in contrast to the world average yield of 2.3 Mg ha�1 for rainfed wetland

rice. However, WARDA (West Africa Rice Development Association, The

Africa Rice Center) has identified 46 promising rice varieties with target

yields of 3 Mg ha�1 or more in rainfed lowlands when moderate inputs are

applied (WARDA, 2002). These high yields have been recorded in some

areas in West Africa (Sakurai, 2006).

d. Production Constraints. Poor water control is a major constraint to

rice intensification in this ecosystem. Many abiotic and biotic constraints

aVect wetland rice production. Abiotic stresses include variable rainfall,

with drought and flood occurrences in the same season. Rainfed wetland

rice is adversely aVected by Fe, Al, and Mn toxicity in wet forest zones

(Buddenhagen, 1986; Sahrawat, 2004a) and in poorly drained soils of coastal

wetlands. Inland salinity and alkalinity are problems in drier and desert

areas (Van Asten et al., 2003). Weeds are the principal biotic constraint,

followed by insect pests (stem borers, African rice gall midge, AfRGM, and

rice bugs) and diseases (blast and brown spot) (WARDA, 1998, 2000). Rice

yellow mottle virus (RYMV) is a major scourge of wetland rice and can

sometimes lead to total crop failure (WARDA, 2000). In addition, rats and

birds are serious problems in all ecosystems.

2. Deepwater and Mangrove Rice Ecosystems

The deepwater ecosystem (Fig. 6) covers several environments where rice

is planted, which is adapted to increasing water depths of 1.0 m or more for

durations of 10 days to 5 months. These rice plants must have the ability to

elongate rapidly to stay above the water surface. ‘‘Floating rice’’ can elon-

gate up to 5 m and form adventitious roots that can absorb nutrients directly

from the floodwater in addition to regular roots grounded in the soil. No

varieties are available that are adapted to rapid or irregular rise of floodwa-

ter or sediment‐laden floodwater that can cover crops for longer than

10 days in some deepwater areas (McLean et al., 2002).

In low‐lying coastal areas, we can diVerentiate perennially fresh, seasonally

saline, and perennially saline tidal wetlands where rice plants are subject to

daily tidal submergence. Plants in tidal lands do not elongate greatly, but

tillering and tiller survival may be reduced in saline soils. In problem soils

(acid sulfate and sodic or alkaline soils), excess water accumulates in fields due


to poor drainage, but no prolonged submergence occurs (McLean et al., 2002).

Al or Fe toxicity is a serious risk when acid sulfate soils of coastal wetlands

are drained (Sahrawat, 2004a), whereas deep peat soils constrain rice

production in high‐altitude areas.

a. Deepwater and Mangrove Swamp Rice Area. Worldwide, about

11–14 million ha will come under deepwater ecosystems. In SSA, about 0.63

million ha are estimated to be aVected by excess flooding, tidal submergence,

saltwater intrusion, and salinity and acid sulfate soils; these ecosystems cover

an estimated 9% of the total rice area in SSA (Table V). Some parts of the

floodplains of the Niger River, the low‐lying wetlands of Madagascar, and

the poorly drained inland basins of Chad, Guinea, Mali, Niger, and Nigeria

have deep flooding, whereas the low‐lying coastal wetlands of East and West

Africa are aVected by salinity and alkalinity due to seawater intrusion.

Mangrove swamps constitute about 49% of the rice land in Guinea Bissau,

14% in the Gambia, and 13% in Guinea (Defoer et al., 2002).

b. Cropping Systems. Only rice is grown in the rainy season. The type,

depth, and duration of flooding determine the rice varieties grown. Specific

rice varieties with diVerent elongation ability are selected for deepwater

(about 1.0 m) and very deepwater (1–5 m) conditions. When flooded, deep-

water rice varieties can elongate 0.02–0.03 m per day, while floating

rice varieties elongate rapidly up to 0.2 m per day (McLean et al., 2002).

Non‐elongation‐type rice varieties with submergence tolerance (Xu et al.,

2006) are needed for freshwater tidal wetlands where flash floods are of

short duration (less than 2 weeks), whereas salt‐tolerant varieties should be

selected for coastal saline lands, including mangrove swamps. In the drier

mangrove areas (e.g., Casamance in Senegal, Guinea Bissau, and the

Gambia) ofWest Africa, farmers plant rice on ridges tomitigate the problems

of Fe toxicity and salinity (WARDA, 2002). During the dry or winter season,

vegetables or legumes can be grown in deepwater areas. In salt‐aVected areas,

the lands are too dry or saline for cropping in the DS.

c. Cultivation Practices and Yields. Deepwater rice and floating rice

aremainly grown in deepwater areas.With the onset of rains, the land is plowed

and harrowed and dry rice seeds are sown by broadcasting. With the moisture

from rainfall, the seeds germinate and the seedlings start growing. If early

rainfall is regular and adequate for land preparation by puddling, seedlings

raised in nurseries are transplanted.Generally, flooding occurs in the later stages

of plant growth and can last for several months. Crop survival and productivity

depend on the age of the rice crop when inundation starts, the rate of rise of


the water, and the depth and duration of the flood. Sudden or flash flooding

can completely destroy the crop at any stage. In some areas, the floodwater

may be loaded with sediments that can cover the leaves and obstruct plant

photosynthesis (McLean et al., 2002). Only minimal or no inputs are applied to

deepwater rice crops due to the high uncertainty of harvests. Once mature,

panicles are harvested, dried, and threshed. Farmers go by canoe or wait until

the water recedes to harvest the panicles of floating rice (Murray, 2005).

Tidal rice is cultivated during the rainy season in the coastal wetlands of

East and West Africa. Tidal rice can tolerate submergence or flash floods to

a great extent. Areas with saltwater intrusion from the sea require salinity‐tolerant rice varieties. About 35‐ to 40‐day‐old rice seedlings raised in

nurseries are transplanted in prepared main fields at 3 or more seedlings

per hill (Gibba, 2003). In areas of poorly drained and acid sulfate soils,

seedlings are transplanted on ridges to reduce Al and Fe toxicity (WARDA,

2002). It is recommended to apply 68‐22‐22 kg ha�1 of N‐P‐K to mangrove

rice in the Gambia (Gibba, 2003). Other practices are similar to those for rice

in the rainfed wetland ecosystem.

NonirrigatedWS rice yields range from 0 to 4.0Mg ha�1 depending on the

season, location, and rice type. Floating rice yields are low, 1.0–2.5 Mg ha�1.

Yields of tidal rice vary widely and complete crop failure can occur in salt‐aVected coastal wetlands. Although the mean rice yield is 1.0 Mg ha�1 in

mangrove swamps of the Gambia, improved rice varieties with adequate

fertilization can yield 3.2–3.3 Mg ha�1 in research plots (Gibba, 2003).

WARDA has identified 341 promising rice varieties with target yields of

3 Mg ha�1 or more in mangrove swamps (WARDA, 2002).

d. Production Constraints. Major production problems in deepwater

areas are submergence, salinity, acid sulfate soils, and Fe and Mn toxicity in

coastal wetlands (Sahrawat, 2004a), and peat soils and cold injury at the

seedling stage in high‐altitude areas (Balasubramanian et al., 1995). Farmers

obtain low and extremely variable yields from nonirrigated WS rice crops

due to the use of low‐yielding but adapted traditional varieties, the applica-

tion of few or no inputs, and multiple environmental stresses—soil problems

and unpredictable combinations of drought and flood. There is a lack of

suitable plant types tolerant of submergence, salinity, acidity, Fe and Mn

toxicity, and cold at the seedling stage (in highlands).

3. Irrigated Wetland Rice Ecosystems

Irrigated rice is grown in bunded fields with assured irrigation for one or

more crops per year. Usually, farmers try to maintain 0.05–0.1 m of water

in rice fields. Irrigated rice areas are concentrated mostly in the humid,


subhumid, semiarid, and high‐altitude tropics of the continent. Dams across

rivers, diversion of water from rivers, or tube wells provide water for irriga-

tion. We can distinguish three types of irrigated rice ecologies in SSA: the

irrigated rice in the arid and semiarid Sahel, the irrigated rice in the humid

forest and savanna zones (Defoer et al., 2002), and the irrigated rice of the

tropical highlands (Balasubramanian et al., 1995).

� Irrigated wetland rice in the Sahel is akin to DS fully irrigated rice in Asia.

In the Sahel, solar radiation is high, water control is good, mechanization

is widespread, pests are less prevalent, and input use is relatively high.

Farmers are organized and infrastructure is well developed. About half of

the irrigated rice area in the Sahel is direct seeded and the rest transplanted.

Only 10% of the area is double cropped (Defoer et al., 2002). Per‐season rice

yields are high, 5–8 Mg ha�1 in research plots and 4–5 Mg ha�1 in farmers’

fields vis‐a‐vis potential yield of 8–12 Mg ha�1 (Haefele and Wopereis,

2004). Mean rice yields in the OYce du Niger in Mali have increased from

2 Mg ha�1 in 1977 to 6 Mg ha�1 in 2002 (Defoer et al., 2002). However, in

the DS, evapotranspiration is high and water consumption is considerably

greater than in the WS. In addition, extreme temperatures limit rice yields

in the WS and DS in some parts of the Sahel.

� Irrigated wetland rice in the humid forest and savanna zones is mostly

transplanted. Irrigation schemes are small and located near main roads

and towns. In the WS, rainfall is the main source of water for crop growth,

and irrigation is used as a supplement during crop establishment and early

crop growth periods as well as during mid‐season dry spells. Both the

potential yields of 5–8 Mg ha�1 per season and the actual yields of around

3 Mg ha�1 per season are relatively lower for irrigated rice in the forest

and savanna zones than in the Sahel (Defoer et al., 2002), mainly due

to lower solar radiation, poorer water control, and higher pest incidence.

In addition, iron toxicity is a constraint in irrigated wetland rice in the

savanna and humid zones of West Africa, where tolerant varieties and

nutrient management showed promising results on a long‐term basis

(Sahrawat, 2004a; Sahrawat et al., 1996).

� Irrigated wetland rice in tropical highlands, in East and Central Africa and

Madagascar, is grown on higher elevation marshlands or inland valley

swamps at 700–900 m above msl (low altitude) and 900–>1600 m above

msl (medium altitude). In well‐developed marshlands, rice land is terraced

and fields are fairly level; small earth dams built across streams and small

rivers at the higher level provide good water control and irrigate from

50 to >1000 ha. There are two seasons: the WS is from July to December

and the DS from January to June. Water supply from rainfall and irriga-

tion is good during the WS and erratic during the DS; flooding may be a


problem in the WS in undeveloped marshlands. All wetland areas (100%)

are planted to rice in the WS and only 60–70% of the area in the DS; in the

remaining area,WS rice is rotated with wheat, maize, potato, or vegetables.

Low temperature or cold injury often aVects the seedlings in the nursery

or main field in June–July. As elsewhere in SSA, P is the most limiting

nutrient to rice production in highlands. Achievable rice yields are high

(7–9 Mg ha�1) in higher elevation marshlands because of warm days

(20–30�C) and cool nights (10–20�C) and longer duration (150–180

days). Rice yields decrease with increasing OM content: 7.3 Mg ha�1

per season in soils with OM < 40‐g kg�1 soil, 6.1 in soils with OM

between 40‐ and 80‐g kg�1 soil, and 4.7 in soils with OM > 80‐g kg�1

soil (Balasubramanian et al., 1995).

a. Irrigated Wetland Rice Area. Globally, the harvested irrigated rice

area of 79 million ha produces more than 75% of the world’s rice output of

600 million Mg or more. In SSA, an estimated 19.8% of the cultivated rice

area was irrigated (1.42 million ha) during 1995–2004 (Table V). Most of the

WS rice areas are located in the rainforest and moist savanna zones of SSA.

About 60% of the DS irrigated rice area of West and Central Africa is found

in the Sahel, Sudan, and savanna zones (WARDA, 2002). High‐altitudeirrigated rice is found in East and Central Africa andMadagascar. Countries

with significant irrigated rice areas are Madagascar (621,764 ha), Nigeria

(419,288 ha), Mali (80,366 ha), Guinea (49,550 ha), Senegal (39,600 ha), and

Cote d’Ivoire (35,063 ha) (Table VI).

b. Cropping Systems. Rice is the main crop during the rainy season

and the land is left fallow for the rest of the year. The rice–rice‐fallowcropping system is practiced in double‐cropped irrigated wetlands of the

Sahel (Defoer et al., 2002). Rice may be rotated with maize, soybean, or

vegetables in inland valley bottoms of West Africa. In double‐cropped areas

of tropical highlands (East and Central Africa and Madagascar), two rice

crops are grown or WS rice is rotated with potato, wheat, soybean, or

vegetables in the winter–spring season (Balasubramanian et al., 1995).

c. Cultivation Practices and Yields. Rice fields are soaked with water,

plowed, puddled, and leveled before crop establishment. Compost and

animal manure, if applied, are incorporated into the soil during land prepa-

ration. Farmers use hand tools, animal‐drawn implements, or hand tractors

to prepare the land. Large tractors are used only in large public and private

sector irrigation schemes. Most of the WS irrigated rice is transplanted in


rainforest and savanna zones and coastal plains, whereas 50% of the irri-

gated rice in the Sahel is direct seeded (Defoer et al., 2002). Seedlings are

prepared in nurseries and 20‐ to 30‐day‐old seedlings are manually trans-

planted in main fields. Farmers weed their rice fields manually and apply

some amount of fertilizers and pesticides, depending on availability and cost

in local stores. Herbicide use to control weeds is minimal. At maturity, rice

is harvested, dried, and threshed manually. In the Sahel of West Africa,

mechanization is widespread, especially for land preparation and threshing

(Defoer et al., 2002).

With good water control and crop management, potentially irrigated DS

rice yields in the semiarid Sahel zones can be as high as 8–12Mg ha�1 (Haefele

and Wopereis, 2004). WARDA has identified 21 varieties with target yields

higher than 5 Mg ha�1 for irrigated rice in the Sahel and 426 varieties with

yields higher than 4 Mg ha�1 for irrigated lands in humid and subhumid

forest zones (WARDA, 2002). However, in most of the irrigated areas of

SSA, farmers obtain 2–5 Mg ha�1 due to irregular irrigation, poor soil and

crop management, and inadequate input use (Miezan and Sie, 1997). The gap

between attainable and average farmers’ yields is 2–6 Mg ha�1 in the Sahel,

2–5 Mg ha�1 in the rainforest and savanna zones (Defoer et al., 2002),

and 2–6 Mg ha�1 in the tropical highlands (Balasubramanian et al., 1995).

d. Production Constraints. Many of the irrigated rice production con-

straints are similar to those in Asia: poor land preparation, leveling, and

irrigation management; inadequate drainage leading to the development of

salinity and alkalinity (inland basins and coastal wetlands); poor manage-

ment of production inputs; yield instability due to weeds (in direct‐seededrice), insect pests, and diseases; and deteriorating irrigation infrastructure,

especially in large public irrigation schemes (Defoer et al., 2002). P deficiency

in all soils, N and P deficiency in mineral and slightly organic hydromorphic

soils, Fe toxicity at poorly drained sites, and high OM content in peat soils

limit irrigated rice yields in the tropical highlands (Balasubramanian et al.,

1995; Sahrawat, 2004a; Sahrawat et al., 1996). K or Si deficiency increases

the susceptibility of rice crops to diseases. In addition to blast disease,

Africa‐specific biotic constraints include AfRGM, RYMV, and glume dis-

coloration. Stem borers, rats, and birds are other pests that attack rice in all

ecosystems.

Many large public sector irrigation projects have not been successful due

to a combination of factors (Defoer et al., 2002). As a result, irrigated rice

yields have declined from more than 7 Mg ha�1 at the start of many irri-

gation projects to less than 3 Mg ha�1 after a few years. Smaller farmer‐managed irrigation schemes may be a viable alternative for sustainable

irrigated rice production inmanyAfrican countries. At the same time, rigorous


socioeconomic studies exploring the causes for failure of large‐scale irrigationschemes are called for.

VI. RICE PRODUCTION CONSTRAINTS IN SSA

Biophysical, management, human resource, and socioeconomic/policy

constraints plague rice farming in SSA.

A. PHYSICAL, BIOLOGICAL, AND MANAGEMENT CONSTRAINTS

Physical, biological, and management constraints vary with rice ecosystems

as discussed above in Section V.

B. HUMAN RESOURCE CONSTRAINTS

Particularly serious is the lack of researchers. As is pointed out by

Evenson and Golin (2003), the ratio of researchers to extension workers is

much lower in SSA than in Asia. This is truly a serious problem because the

lack of profitable technology, but not the lack of extending it, is the most

basic constraint to improving farming eYciency in SSA. Once new profitable

technologies are developed, demand for extension services will increase.

In such a situation, it is expected that capacity enhancement programs for

extension workers, which will have high payoVs, will be undertaken.The lack of education among rice farmers is another major constraint, as

better‐educated farmers are more willing to adopt new technologies (Schultz,

1975). According to the Green Revolution experience in Asia, however, the

role of education becomes less important over time as the new technology

is widely adopted (David and Otsuka, 1994). Given the substitutability

between farmers’ education and extension services, and the lack of education

among farmers in SSA, strengthening the extension system is likely to be an

appropriate strategy once new technologies become available. In the longer

run, the continuous development of new technologies will attract educated

farmers to engage in scientific rice farming and stimulate investments in

schooling of children.

Other human resource‐related constraints are as follows:

� Weak or nonexistent research‐extension‐farmer linkage

� Poor or no farmer organizations

� Lack of public–private partnerships


� Reduced labor availability due to poor nutrition and/or diseases such as

AIDS, cholera, malaria, bilharzia, and so on.

C. SOCIOECONOMIC AND POLICY CONSTRAINTS

In addition to biophysical and human resource constraints, rice produc-

tion in SSA is aVected by socioeconomic and policy constraints:

� Unfavorable input and output pricing policies at the national level. Low

output prices vis‐a‐vis high and rising input prices reduce profit and

the competitiveness of smallholder farms in local, regional, and global

markets.

� Limited access to credit, inputs (seed, fertilizers, pesticides, implements,

and so on), markets, and market information.

� Poor rural infrastructure and transportation.

This unfavorable price structure reflects the ineYcient marketing systems

in SSA. The establishment of eYcient marketing systems requires trust

between local traders and farmers and between local and urban traders,

because dishonest behavior, such as cheating on product quality and late

delivery, can easily occur in any transaction (Hayami and Kikuchi, 2000).

To prevent such behavior, trust must be developed through long‐termand repeated transactions. Prerequisites for such development are (1) the

improvement of rural infrastructure and transportation systems and (2) the

availability of fertilizer‐responsive‐improved varieties and eYcient tech-

nologies that enhance the profitability of long‐term transactions between

farmers and traders. Experience shows that socioeconomic institutions are

not rigid, but are subject to change as new profitable opportunities arise not

only in Asia (Hayami and Kikuchi, 1982; Hayami and Ruttan, 1985) but

also in SSA (Otsuka and Place, 2001). How such development may take

place and whether any major obstacles to change exist in SSA need to be

analyzed through collaborative research between social scientists and

researchers engaged in the development of new rice technologies.

VII. RICE RESEARCH AND TECHNOLOGYDEVELOPMENT DURING THE PAST 20 YEARS

The two leading international rice R&D institutions—International Rice

Research Institute (IRRI) and Africa Rice Center (WARDA)—complement

each other in developing the rice sector in SSA and bringing concrete

benefits to its rice farmers and consumers. During the past two decades,


both centers have generated many rice research outputs and technologies

through individual and collaborative research with national agricultural

research institutes (NARIs). These research findings and technologies are

discussed briefly in this section.

A. RICE GERMPLASM, BREEDING, AND VARIETY DEVELOPMENT

1. Plant Types and Traditional Rice Varieties of SSA

The genus Oryza has two cultivated species, O. glaberrima Steud (African

rice) and O. sativa (L.) (Asian rice), and 21 wild taxa of Asian and African

origin. Of the 21 wild rice species, seven originated in SSA and the rest in

Asia. The seven African wild rice species and their characteristics are given

in Table VII. These wild species carry genes for specific traits, for example,

resistance to biotic and abiotic stresses, and these genes are valuable in

interspecific crossing (Khush, 1997).

O. glaberrima is the African indigenous species, propagated from its

original center, the upper‐middle delta of the Niger River, and extended

toward the Senegal, Gambia, Casamance, and Sokoto basins (Carpenter,

1978; Murray, 2005). It has been cultivated for 3500 years (Dembele, 1995;

Porteres, 1956). O. glaberrima has no subspecies. It is adapted to African

environments but prone to lodging and grain shattering when compared

with O. sativa (Sie, 1991). It possesses early plant vigor and resistance to

African stresses such as drought, blast, RYMV, nematodes, and insects

(Adeyemi and Vodouhe, 1996). These qualities are valuable in interspecific

crossing.

O. sativa has two subspecies—indica and japonica—with a continuous

array of intermediates. The many agroecotypes of O. sativa are adapted to

various growing conditions and improved varieties derived from them are

highly productive. The japonica is adapted to rainfed drylands and indica to

the aquatic ecology of SSA. But they are susceptible to many abiotic and

biotic stresses in SSA (Sie, 1991).

O. glaberrima is now being replaced by the Asian rice O. sativa introduced

by European traders into SSA around the sixteenth century (Buddenhagen,

1986; Porteres, 1970). Some farmers grow both Asian and African rice side

by side to meet their varied needs and to tackle adverse conditions. They like

the African rice for its fast early growth that can suppress weeds, its shorter

duration, its resistance to diseases, and the nutty flavor of its grains (Nyanteng

et al., 1986).

Varietal classification is done based on the characteristics of the two

cultivated species and cultural practices in the field—time of inundation,

Table VII

African Wild and Cultivated Rice Species and Their Origin, Distribution, Plant Type, Grain Features, and Valuable Genes for Interspecific Crossing

Species 2n Genome

Origin and

distribution

Plant type and grain

features

Valuable donor

genes References

I. Wild species

O. barthii

(O. breviculata)

A. Chev. and

Roehr. (ancestor

of O. glaberrima)

24 AgAg West African

Savanna and Sahel

(swamps and

waterholes)

An annual grass; self‐fertile;long grains w/awns,

shattering; dormancy

Resistance to GLH,

bacterial blight;

drought avoidance

Khush (1997);

Vaughan (1994)

O. longistaminata

A. Chev. and

Roehr. (possible

ancestor of

O. barthii)

24 AgAg Tropical Africa and

Madagascar

A tall, erect perennial

w/rhizomes; cross‐pollinated; long thin

grains w/awns; shedding

Resistance to

bacterial blight;

drought avoidance

Besancon et al.

(1978); Khush

(1997); Vaughan

(1994)

O. punctata Ktoschy

ex Steud.

24

48

BB

BBCC

East and West

Africa;

Madagascar

(forest and

waterholes)

Both annual and perennial;

long, narrow grains

Resistance to BPH,

leafhopper

Katayama (1990);

Khush (1997);

Vaughan (1994)

O. brachyantha

Chev. and Roehr.

24 FF West, Central and

South‐easternAfrica

A short, slender annual;

small and very narrow

grains w/long awns

Resistance to yellow

SB, leaf folder,

whorl maggot, of

tolerance to

lateritic soil

Khush (1997);

Vaughan (1994)

88V.BALASUBRAMANIA

NETAL.

O. stapfii Roschev. 24 AgAg West Africa A perennial weedy species – Bradenas and Chang

(1966)

O. eichingeri 24

48

CC

BBCC

East, Central and

S.E. Africa;

Sri Lanka

Short, sturdy annual and

perennial; short grains

– Vaughan (1994)

O. schwein furthianaa 48 BBCC Tropical Africa A perennial –

II. Cultivated species

O. glaberrima Steud. 24 AgAg West Africa An annual; dryland erect

photoinsensitive; and

floating photosensitive;

no second or third

branching in panicles;

short grains, shedding

Cultigen; fast early

growth, weed

suppression

Bradenas and Chang

(1966); Khush

(1997); Vaughan

(1994)

O. sativa (L.) 24 AA Asia Indica and japonica

subspecies w/

intermediates; erect to

floating; traditional and

improved

Cultigen; forked

branches in

panicle, no grain

shedding

Khush (1997);

Vaughan (1994)

INCREASIN

GRIC

EPRODUCTIO

NIN

SUB‐SAHARAN

AFRIC

A89


flood duration, maximum water depth, and level of soil fertility. On the basis

of these criteria, five varietal groups are recognized in SSA:

1. ‘‘Rainfed’’ varieties called ‘‘mountain rice’’ or ‘‘dryland rice’’ are often

cultivated in watershed areas and along forest galleries and in upper parts

of inland valleys where flooding is not common. These plants are low in

tillering and suited to direct seeding.

2. ‘‘Early‐duration erect varieties adapted to a submerged environment’’ are

often found on valley fringes with hydromorphic soils having variable

moisture regimes.

3. ‘‘Season‐erect varieties’’ are often planted on lower parts of the topose-

quence than the previous ones and are subject to flooding (0.5‐ to 0.8‐mwater depth). They are suitable for rainfed wetlands.

4. ‘‘Late‐duration erect varieties’’ are mostly adapted to river floodplains

and deepwater areas.

5. ‘‘Floating’’ varieties capable of surviving floods remain above water level

even at significant water depths (1 to>3 m).O. glaberrima is predominant

in this category.

2. Glaberrima � sativa Crosses and the Development of NERICAVarieties for African Drylands

In 1991, Dr. Monty Jones of WARDA led a team of scientists in a new

breeding eVort to unlock and combine the genetic potential of Asian and

African rice. Key to the eVort was WARDA’s rice Gene Bank with 16,000

rice varieties preserved in cold storage, and duplicated at the International

Institute for Tropical Agriculture (IITA) in Nigeria and at IRRI in the

Philippines. Among the preserved varieties are 1500 O. glaberrima lines.

Jones and his group used molecular biology to overcome sterility, the

main problem in interspecific crossing, and to speed up the breeding cycle.

They made ‘‘wide crosses’’ of the African and Asian rice, then removed the

fertilized embryos by embryo rescue and grew them in artificial media. They

then backcrossed the progeny twice to the Asian parent to recombine the

genetic backgrounds of the two distinctly diVerent species. Backcrossing

allowed the introgression (merging) of useful genes such as the wide, droopy

leaves from the rugged O. glaberrima into the more productive O. sativa

subspecies japonica background. Anther culture helped breeders ‘‘fix’’ prog-

eny lines rapidly and retain recombinant lines—with the combined traits of

both the African and Asian parents (Fig. 7). With conventional breeding

where the progeny of a cross segregates into diVerent plant types, it takes 5–7generations to isolate, purify, and select a line with a desired combination of

genetic traits. For dryland rice, this could mean 5–7 years because usually

only one crop can be grown per year. With anther culture, a line can be

Hybridization scheme for the production of NERICAs

Oryza glaberrima African rice

Oryza sativa Asian rice

O. sativa

O. sativa

F1

BC1F1

BC2F1

BC2F1BC2F6

Anther culture

Ho Fixed lines(new plant type)

NERICA

Pedigree selection

×

×

×

Figure 7 Hybridization scheme for producing the new rice (NERICA) varieties for SSA

drylands.


selected after only one generation, and a new variety developed in 18–24

months. By the mid‐1990s, WARDA scientists were testing the new rice for

Africa (NERICA) in rainfed drylands (WARDA, 2001–2002).

Traits of dryland NERICA varieties: The genetic diVerences of the two

distant species crossed gave NERICA varieties high levels of heterosis or

hybrid vigor for faster growth, higher yield, and more resistance to stresses

than either parent. The NERICA varieties have raised the ‘‘yield ceiling’’ of

dryland rice by 50%, from the current level of 4 Mg ha�1, due to longer

panicles with forked branches bearing 2–3 grains each and more grains per

panicle (Table VIII). The new varieties are taller than O. glaberrima, which

makes harvesting easier—especially if the woman farmer has a baby

strapped to her back.

The shorter duration (90–100 days) of NERICA varieties allows farmers

to grow two crops during one rainy season—one rice crop and a post‐ricedryland crop such as grain or fallow legumes that can smother weeds and

add up to 60 kg of biologically fixed N per hectare. Each hectare of well‐managed rice–legume rotation could save 4 ha of fallow land from clearing.

Projections on the spread of NERICA varieties and rice‐fallow legume

rotations in West Africa indicate that by 2010 the total area of land saved

will be about 15,000 ha (WARDA, 2001).

O. glaberrima is highly tolerant of drought. When faced with drought, the

thin leaves ‘‘roll’’ quickly to retain water and the thin roots grow deep into

the soil to explore water. The total length per gram of O. glaberrima roots

can reach about 150 m in contrast to 100 m for O. sativa roots. When the

rains come after drought, the O. glaberrima recovers faster because the

replacement of the thin leaves and roots requires less water and nutrients.

Table VIII

Improved Traits of the O. glaberrima � O. sativa Crosses (NERICAa)

Traits O. glaberrima parent O. sativa parent

O. glaberrima � O. sativa crosses

(NERICA lines)

Inherited advantages of

NERICA lines

Plant height Short Short Taller than both parents Facilitates harvesting of panicles

without bending

Leaves Droopy, wide Erect Droopy, wide lower leaves at

early vegetative growth and

erect upper leaves at

reproductive phase

Early weed suppression and

higher photosynthesis at

reproductive phase > higher

grain yield

Stems Strong, sturdy Weak, thin Strong Help bear heavy panicles,

no lodging

Tillering Low High High More productive tillers,

higher yield

Panicle type Medium long with no

forked branches

Long with forked

branches

Longer than either parent with

forked branches

Higher yield

Grains per branch Single 3–4 3–4

Grains per panicle Low (75–180) High (100–250) Very high (up to 400)

Grain shattering

at maturity

High No No No loss of grain at harvest

Duration (days) 150–170 120–140 90–100 Higher yield per day, allows

double cropping

Drought tolerance

traits

Thin leaves and long thin

roots (150 m g�1), thin

leaves and roots recover

fast with rains after

drought

Medium thick leaves,

short roots (100 m g�1),

slow recovery after

drought

Thin leaves and long thin roots,

thin leaves and roots recover

fast with rains after drought

Good drought tolerance and

avoidance, fast recovery with

rains after drought

aNERICA, New Rice for Africa.

92V.BALASUBRAMANIA

NETAL.


The NERICAs have inherited the thin leaves and roots of O. glaberrima

(WARDA, 2001–2002, 2002–2003).

3. Breeding of New NERICA Varieties for African Rainfed Wetlands

Rainfed wetland rice in Africa suVers from variable rainfall, unpredictable

drought and flooding, AfRGM, RYMV, and blast. Most of the traditional

wetland rice varieties grown in the region have a narrow genetic base, which

leads to their vulnerability to drought, diseases, and pests. Some diseases,

such as RYMV, are spreading fast in the region because of the predominant

cultivation of susceptible rice varieties. Therefore, Dr. Sie of WARDA and

his partners crossed specific RYMV‐resistant African rice varieties with

popular—but susceptible—Asian rice (O. sativa subspecies indica) varieties.

As can be envisaged, the initial problem was hybrid sterility (infertile

oVspring of the crosses) because the two rice species have evolved separately

over millennia and are so diVerent that often attempts to cross them do not

lead to reliable variety development (WARDA, 2003–2004, 2004–2005).

The sterility problem is greater when we cross the African rice with indica

than with japonica. The sterility blockage was overcome by backcrossing

(crossing the hybrid with an O. sativa parent) to restore fertility. Some of the

progeny combined the best features of both parents: the droopy leaves and

vigorous early growth (associated with weed competitiveness) typical of the

African rice and the high number of spikelets (indicating productivity) of

the Asian rice. A major scientific milestone was achieved when the screening

for resistance to RYMV under artificial infestation showed that the crosses

had successfully transferred resistance to RYMV into some of the progeny.

A new plant type with high yield potential is now available for wetlands,

endowed with resistance to local stresses, particularly to the dreaded

RYMV. The progeny of O. glaberrima and O. sativa subspecies indica

are better adapted to rainfed and irrigated wetland conditions, while those

of O. glaberrima and O. sativa subspecies japonica are more suited to rainfed

dryland conditions in SSA (WARDA, 2003–2004, 2004–2005).

The shuttle‐breeding approach used between WARDA breeders and

national programs facilitated the fast exchange and evaluation of breeding

lines under diVerent conditions, accelerated the selection process and increased

its eYciency, and helped achieve wide adaptability of new plant types. For

example, in Burkina Faso, about 600 new plant‐type lines were tested in the

wetlands of the Banfora research station for 4 years (2000–2003) and the 20

most promising lines were selected based on yield and resistance to stresses,

especially to RYMV. Lines of the new plant type were also evaluated in other

important rice‐growing countries of West Africa—Mali, Burkina Faso, Togo,

and Senegal—and more than 70 promising lines were selected.


In addition, farmers were involved in the early varietal selection process

through farmer participatory variety selection (PVS). The PVS approach

helped farmers choose varieties that meet their needs and breeders obtain

feedback from farmers regarding their preferences for plant type and grain

characteristics and speed up the fine‐tuning, adoption, and dissemination of

new varieties. The PVS exercise showed clearly that men farmers gave

importance to short growth duration and plant height, whereas women

preferred traits such as good emergence, seedling vigor, and droopy leaves

that indicate weed competitiveness, since they are mostly involved in sowing

and weeding operations.

The three most preferred new plant‐type lines are WAS 122‐IDSA‐1‐WAS‐B‐FKR‐B‐1, WAS 122‐IDSA‐1‐WAS‐2‐FKR‐B‐1, and WAS 122‐IDSA‐1‐WAS‐6–1‐FKR‐B‐1. They have a yield potential of 6–7 Mg ha�1,

good tillering ability, growth duration of 120 days, and an acceptable plant

height; all three varieties showed good resistance to major wetland stresses

and also responded well to N application. Four new wetland NERICA vari-

eties, now oYcially known as the ‘‘WetlandNERICAs,’’ have been released in

Burkina Faso, two in Mali, and three in the Gambia (WARDA, 2003–2004,

2004–2005). The wetland NERICA varieties oVer a powerful new weapon to

rice farmers to manage their complex wetland rice stresses. However, to be

most eVective, they should be used as part of the integrated crop management

(ICM) approach developed by WARDA.

Work continues with genetic engineering and molecular tools to identify

and incorporate traits for various abiotic stresses into elite rice germplasm

and to develop suitable wetland varieties through both interspecific crossing

(crosses between the two cultivated species of rice) and intraspecific cross-

ing (crosses within the species, i.e., between O. sativa varieties). Table IX

provides a summary of ongoing conventional and molecular‐assisted breed-

ing eVorts at IRRI and WARDA to develop rice varieties suitable for

diYcult rice environments in SSA (Gregorio et al., 2006).

4. Development of Improved Irrigated Rice Varieties

Since 1971, IITA has been involved in varietal improvement research for

irrigated rice in Africa and in the national and international varietal‐testingnetwork in the region. The strategy for irrigated rice improvement was to

incorporate resistance to or tolerance of Africa‐specific stresses such as

RYMV, blast, AfRGM, and so on, into promising introductions from Asia

and Latin America (Buddenhagen, 1986). Through this program, IITA has

identified or developed high‐yielding rice varieties suitable for irrigated sys-

tems: ITA 212, ITA 222, and ITA 306, with a duration of 120–130 days, a

Table IX

Priority for Genetic Engineering and Conventional Breeding Approaches for Incorporating

Resistance to/Tolerance of Abiotic Stresses in Rice

Traits for abiotic

stresses

Priority

Comments1 2 3

P deficiency MASa CONb – G � E interactions favor use of MAS

Zn deficiency MAS CON – Genes introgressed from wild species into

O. sativa and MAS under progress

Salinity MAS CON GMRc MAS allows pyramiding genes of QTLs

for diVerent mechanisms of tolerance

Drought MAS CON GMR MAS and GMR under development

through functional genomics

Submergence MAS CON GMR MAS in full implementation with the

identified Sub1A gene

Fe toxicity MAS CON – G � E interactions favor MAS

Al toxicity MAS CON – Genes introgressed from wild species into


Cold tolerance MAS CON – G � E interactions favor MAS

Elongation

ability

MAS CON – Genes introgressed from wild species into


aMAS, DNA marker‐aided selection (includes use of linked markers, and candidate genes or

identified genes).bCON, conventional breeding.cGMR, genetically modified rice.

Adapted from Gregorio et al. (2006).


plant height of 0.97–1.06 m, and a mean yield of 4.7–5.4 Mg ha�1 in national

trials in Nigeria and Cameroon; two Fe‐toxicity‐tolerant varieties, ITA 247

and ITA 249; and two cold‐tolerant varieties, B2161‐C‐MR‐51‐1‐3‐1 and

IR7167‐33‐2‐3 for high‐altitude areas. Donors identified for incorporating

resistance to African stresses were Moroberekan, LAC 23, ITA 235, and CT

19 for RYMV; Cisadane and Eswarakora for AfRGM; and ITA 121 and DJ

12‐539‐2 for stalk‐eyed fly (Masajo et al., 1986).

The NARES introduced a large number of irrigated rice varieties from

abroad—Japan, United States, Thailand, China, Portugal, Spain, Egypt,

and Madagascar. However, most of the current irrigated rice varieties were

introductions of the 1970s through WARDA–INGER (International Net-

work for Genetic Evaluation of Rice) coordinated regional trials in West

Africa (WARDA, 1996). The local irrigated rice‐breeding program initiated

in the mid‐1970 exploited both African and exotic germplasm to develop

improved irrigated rice varieties (Sie, 1994).


5. Germplasm Exchange by INGER‐Africa

In 1975, IRRI launched the global International Rice Testing Program

(IRTP) for the systematic collection, distribution, and testing of rice genetic

materials. Later, it became INGER, with the objectives of promoting global

exchange, evaluation, and use of improved breeding materials originating

from sources worldwide. INGER‐Africa was part of the global program

until it was transferred to WARDA in April 1997. INGER‐Africa had 16

types of regional rice evaluation trials/nurseries targeted for dryland, irri-

gated, rainfed wetland, and mangrove ecosystems and biological stresses of

blast and RYMV. From 1985 to 1996, INGER‐Africa distributed 3726

nursery sets to African countries. Only a few rice varieties adapted to local

conditions were selected by national breeders from the INGER‐Africa nur-

series due to the mismatch between national capacity and needs and the

supply from the program.

A new germplasm exchange mechanism began in 1991 and was formalized

in 1994 at WARDA to modify certain operational aspects of INGER‐Africa

to make it more eYcient and responsive to national needs in SSA. With the

new approach, nurseries are designed to (1) fit NARES’ needs and avoid

overloading their capacity, (2) provide genetic diversity and variability

for key rice ecosystems, and (3) target a supply of valuable germplasm.

In addition, the new mechanism oVers NARES:

� Improved germplasm from a wide range of sources for national breeding

and direct selection of varieties—nursery entries come from several

countries or institutions in Africa (73%), Asia (19%), and Latin America,

Europe, the United States, and other countries (8%)

� A mechanism to screen their own genetic materials for resistance to or

tolerance of specific stresses at reliable hot spot locations in the region

� The means to test the agronomic stability and adaptability of their elite

varieties in regional multilocation trials

� The means to handle segregating populations—F3 populations nominated

by breeders are grown and harvested in bulk for distribution to NARES

on request for in situ selection and advancement nationally.

With the creation of the WARDA research task forces in 1991, members

of task forces who are also members of the new INGER‐Africa meet every

year to report on their results over the previous year and plan their activities

for the following year. This arrangement has increased interactions among

scientists and improved the rate of return of trial results. The NARES’

share of varieties in regional nurseries increased from <10% in 1985 to

about 60% in 2000.

Although most of these rice germplasm materials were bred or selected in

Africa, their parents came from wide sources: India, Sri Lanka, Bangladesh,


Mozambique, Indonesia, Philippines, Thailand, Taiwan, China, Colombia,

Argentina, Brazil, Zaire, Sierra Leone, Cote d’Ivoire, Nigeria, Guinea, Mali,

Senegal, the Gambia, and international research centers such as IRRI, IITA,

WARDA, and the International Center for Tropical Agriculture (CIAT).

Thus, despite limited regional resources invested annually in varietal impro-

vement, 197 improved varieties had been released up to 1999, with more

than 122 during the next 5 years (2000–2004). These results involve only

7 out of 17 WARDA member countries and indicate the eYciency and

eVectiveness of the new approach to germplasm exchange and evaluation

in SSA. In addition to germplasm exchange, INGER‐Africa activities include

(degree, group, and in‐country) training of NARES scientists and technicians

in the region.

B. RICE SEED PRODUCTION AND DISTRIBUTION SERVICES

One of the principal strategies for improving food security in SSA is to

strengthen the seed supply sector (FAO, 1997). Unlike fertilizers and pesti-

cides, which are often available and used, particularly on cash crops, good‐quality seeds are rarely used by farmers in SSA. Guaranteeing farmers access

to good‐quality seed can be achieved only if there is a viable seed supply

system to multiply and distribute seeds of improved varieties and if mechan-

isms to assist farmers in emergency situations have been established. As long

as the seed varieties oVered are well adapted to small‐farm environments and

low‐input crop management practices, other inputs such as fertilizers are less

critical compared to the benefits derived from improved seed.

1. Status of Existing Seed Sector Services and Seed Research

To design realistic strategies for the future development of the seed supply

sector in SSA, it is imperative to assess in‐depth the existing seed sector.

There are formal and informal seed sectors in all countries.

Formal seed supply systems include public sector institutions, such as para-

statal (quasigovernment) seed agencies providing seed certification and

quality control, and the private sector. The formal seed production and

supply programs are organized mostly by the public sector and commonly

assisted by donor agencies. Private companies are also involved in the formal

seed sector, especially in Ethiopia, Madagascar, Malawi, Mozambique,

Nigeria, South Africa, Zambia, and Zimbabwe. However, despite these

eVorts, formal seed supply systems currently meet not more than 5–10% of

the seed needs of farmers in the region.


Most formal seed production projects in SSA failed because of

� The use of the criteria and seed standards of the seed industry of developed

countries, which are diYcult to implement and sustain under developing

country conditions

� The lack of follow‐up of donor‐funded programs to ensure continuity of

activities after a program or project ended

� The concentration of donor‐funded projects exclusively on the formal seed

sector, ignoring the already well‐established informal sector

� The concentration of almost all projects on major crops of commercial

value, neglecting local crops of economic and social importance to small

farmers.

Informal seed supply systems are composed of indigenous strategies to

improve the quality and quantity of seed used by farmers. About 90–95%

of the seed production in almost all countries of SSA is still in the informal

seed supply system.

Seed research: The average investment by SSA countries in agricultural

research is estimated to be less than 3% of gross domestic product (GDP).

Thus, the primary seed research activities in most countries involve variety

development and testing, variety release and registration, variety mainte-

nance, and breeder seed production. Since variety development is time con-

suming and costly, many governments in the region tend to prioritize variety

development research alone according to urgent national needs. As a result,

research strategies are directed to a few cereals and staple food crops only.

2. National Seed Laws and Variety Release Process

Only 25% of the African countries have passed a seed act that stipulates

specific seed regulations that must be satisfied. The remaining 75% of the

countries in SSA do not have legislation governing the production, distribu-

tion, and sale of seeds. In addition, even in most of those countries where a

seed act has been passed, putting the various laws and policies into practice

has been impeded by inadequate enforcement mechanisms and a lack of

logistical, financial, and human resources.

In addition, the variety release process is weak inmany countries, and itmay

take 10 years to release and register a new variety in some countries. The

documentation of new varieties with their origin and agronomic and technical

characteristics is again poor due to the lack of trained staV and resources.

The breeder holds an exclusive right tomultiplication and distribution of seeds.

There is no national strategywith a good awareness campaign to encourage the

production, distribution, and use of good‐quality seeds widely.


C. CROP ESTABLISHMENT

Timely crop establishment is critical for good plant growth and high

yields. In irrigated DS rice areas, optimum planting time can be maintained

by a regular water supply. In rainfed drylands and wetlands, the arrival of

rains decides the time of planting.

Rice is mostly transplanted in irrigatedwetlands and some rainfed wetlands.

Half of the irrigated rice in the Sahel is direct seeded. In transplanted rice areas

of West and Central Africa, research data recommend not to transplant in

August or from November to December to avoid low‐temperature stress

(WARDA, 2002). Good nursery management and transplanting of young

and vigorous seedlings at optimum spacing will increase irrigated rice yields

(Balasubramanian et al., 2005). In mangrove swamps, it is recommended to

plant rice on ridges to improve drainage and to reduce Al and Fe toxicity.

Farmers in Africa prefer direct seeding if suitable methods are available.

In addition to seeding techniques, research must develop technologies to pre-

pare smooth and level seedbeds for direct sowing and control weeds eVectivelyin direct‐seeded rice (Buddenhagen, 1986; Defoer et al., 2002).

In rainfed drylands and wetlands, rice seeds are broadcast, drilled, or

dibbled in prepared dry‐to‐moist soil. All three methods are equally eVectivewhen the optimum seed rate of 50–80 kg ha�1 is used (WARDA, 2002).

In drilled and dibbled rice fields, eVective weed control is possible with

interrow cultivation.

D. NUTRIENT MANAGEMENT

Unlike dryland soils, which are mostly acidic, infertile, and highly prone

to erosion, it is easier to keep soils fertile and stable in wetlands. Naturally,

water and nutrients accumulate in wetlands; in addition, N is made available

through microbial N fixation, P through increased solubility under reduced

conditions, and K and other bases are supplied by rain and irrigation water.

Of the 16 known elements required for plant growth, N, P, K, S, and Zn

are important for rice; Si is becoming deficient in intensively cultivated rice

areas of Asia (e.g., Sri Lanka). Other elements taken up by rice crops are

Ca, Mg, Fe, and Mn. The importance of boron (B) to flooded rice is not

established. To produce 1 Mg ha�1 of grain yield, rice crops remove on

average 19.1 kg ha�1 of N, 2.8 of P, 23.6 of K, 3.9 of Ca, 5.2 of Mg, 0.50 of

Fe, 0.55 of Mn, and 0.03 of Zn. Nutrient uptake by irrigated and dryland

rice is similar for N, Mn, and Zn; irrigated rice removes more P, K, Ca, and

Mg than dryland rice per megagram per hectare of grain yield and the

reverse is true for Fe only (Table X) (Sahrawat, 2000). Dryland rice seems

to be more eYcient in using P for grain production. In this study, the

Table X

Nutrients Removed (in Grain þ Straw) by Irrigated Wetland and Rainfed Dryland Rice Crops

per Megagram per Hectare of Grain Yield in Cote d’Ivoire, West Africa, 1994 and 1996

Nutrient

Nutrients removed Nutrient element harvest index (%)

Irrigated ricea Dryland riceb Irrigated ricea Dryland riceb

N (kg ha�1) 18.9 19.4 57 60

P (kg ha�1) 3.4 2.1 67 71

K (kg ha�1) 28.7 18.5 9 11

Ca (kg ha�1) 4.8 3.0 17 15

Mg (kg ha�1) 6.8 3.6 28 30

Fe (g ha�1) 384 616 48 21

Mn (g ha�1) 561 541 21 8

Zn (g ha�1) 30 25 50 38

aIrrigated rice: Mbe site; Ultisol; cv Bouake 189; 1996 DS; Yield: 6.77 Mg ha�1.bDryland rice; Man site, Alfisol; cv WAB 56–50; 1994 WS; Yield: 3.14 Mg ha�1.

Data derived from Sahrawat (2000).


nutrient element harvest index [amount in grain/amount in (grain þ straw)]

was the highest for P, followed by N and Zn, indicating the presence of a

higher proportion of these three elements in the grain. About 90% of K, 85%

of Mn, 84% of Ca, 71% of Mg, and 65% of Fe were retained in the rice straw

(Sahrawat, 2000). Thus, the return of straw to rice fields will help reduce the

depletion of K, Ca, and Mg from rice soils.

For any system to be sustainable, the export of nutrients from the system

through harvests must be balanced by nutrient additions. Integrated nutrient

management considers all sources of nutrients interacting in a system.

Essentially, it involves three principles (Smaling et al., 2002):

� Add new nutrients to the system—composts and manures from outside the

field, fertilizers, N fixation in wetland rice fields, and biological N fixation

by legumes

� Save nutrients from being lost from the system—soil erosion control, return

of crop residues, planting deep‐rooted crops to reduce leaching losses

� Recycle nutrients within the system tomaximize productivity and nutrient‐useeYciency.

Using the three principles, several nutrient management approaches

have been developed: ecosystem‐based and toposequence‐based nutrient

management developed by WARDA, Benin; site‐specific nutrient manage-

ment (SSNM) developed by IRRI, Philippines; integrated soil fertility man-

agement (ISFM) developed by the International Fertilizer Development

Center (IFDC)‐Africa, Togo; and integrated plant nutrient systems (IPNS)


developed by the FAO, United Nations, Rome, Italy. We shall briefly look

at the first three approaches for rice in SSA.

1. Ecosystem‐Based Nutrient Management

Dryland rice ecosystem: Dryland rice soils (Oxisols and Ultisols) are

invariably acidic, infertile, and highly P‐fixing (Sahrawat et al., 2003). The

application of rock‐phosphate (rock‐P) or other P fertilizers is critical before

crops respond to N and other nutrients. Finely ground and moderately to

highly reactive rock‐P can be applied to acid dryland soils (Diamond, 1985).

Rock‐P applied to legume fallows benefits the following rice crops more than

its direct application to rice crops (Somado et al., 2003). Research recom-

mends an application of magnesium limestone at 150–200 kg ha�1 for

slightly acidic soils and 2–3 Mg ha�1 for highly acidic soils before fertilizers

are applied to rice crops. Recommended fertilizer rates for dryland rice

range from 40‐36‐64 to 90‐27‐36 kg ha�1 of N‐P‐K (WARDA, 2002).

P and K are applied at planting, while N is to be applied in 2–3 splits at

basal, mid‐tillering, and panicle initiation (PI) stages. The field must be

weeded before applying N fertilizers. However, farmers apply little or no

fertilizer and thus mine the soil continuously. At least, they should be

encouraged to apply available crop residues, composts, and animal manures

(Erenstein, 2003); improve short‐season fallows by planting legume cover

crops (Akanvou et al., 2001a; Carsky et al., 2001; Somado et al., 2003);

rotate or intercrop rice with legumes (Akanvou et al., 2001b); and mulch

soils with crop residues to preserve soil fertility (Erenstein, 2003).

Rainfed wetland ecosystem: P is deficient in most wetland (Oxisols, Ulti-

sols, Vertisols, and certain Inceptisols) and acid sulfate soils (Sulfaquepts,

Sulfaquents). P availability is controlled by P sorption–desorption kinetics

and solubility rates of various Al, Fe, and Ca phosphates in soils (Diamond,

1985). P adsorption by soils is related to their mineralogy: quartz ¼ Al‐freeOM < 2:1 clays < 1:1 clays < crystalline Fe‐ and Al‐oxides < amorphous

Al‐ and Fe‐oxides (Juo and Fox, 1977). When the soil is submerged, P

availability increases from ferric and aluminum phosphates due to increasing

pH in acid to neutral soils and from calcium phosphates due to decreasing pH

in basic calcareous and alkaline soils (Ponnamperuma, 1972). The incor-

poration of P fertilizers during land preparation or surface application until

28 days after transplanting or dipping of seedling roots into a soil‐P slurry

before transplanting is a good practice for P application to flooded rice

crops. In degraded wetland soils with high P‐fixing capacity, P should be

applied in two splits—at planting and PI (WARDA, 2002).

Recommended N rates for wetland rice range from 40 to 90 kg ha�1,

applied in 2–3 splits (at planting, mid‐tillering, and PI). For rice crops in


mangrove swamps and tidal wetlands, 40–80 kg ha�1 of N in 3–4 splits and

40 kg ha�1 of P as basal are recommended for they are the most limiting

nutrients in this ecosystem (WARDA, 2002). Rice straw incorporation into

soils may maintain soil K at low‐yield levels; but K fertilizer needs to be

applied along with N and P to get high rice yields (Kyuma et al., 1986).

In addition to NPK, plants require low amounts of S and micronutrients

such as Zn, Fe, and so on. Soil submergence increases the availability of Fe,

Mn, and Mo, but decreases that of S, Zn, and Cu; it also reduces Fe and Mn

toxicity in acid soils, including acid sulfate soils (Neue and Mamaril, 1985).

In addition, the slow decomposition of OM accumulated in flooded soils

(Sahrawat, 2004b) may supply some of the micronutrients to rice plants.

Thus, the need for the application of S and micronutrients to rice crops must

be based on the knowledge of their established deficiency in soils. Nutrient

forms in soils and sources for application, critical values for their deficiency

and toxicity, and application methods are summarized in Table XI.

Irrigated rice ecosystem: Inadequate nutrient application is among the key

constraints to achieving high yields in irrigated rice where fertilizer use is

most profitable (Haefele et al., 2000, 2001, 2002). Although rice varieties and

production technologies, including fertilizer rates, were introduced from

Asia, they were gradually adapted and modified to the local biophysical

and economic conditions (Haefele and Wopereis, 2004). Farmers’ N rates

varied from 37 to 251 kg ha�1, P from 9 to 66 kg ha�1, and K from 0 to

7 kg ha�1 in Senegal and Mauritania, which represent the irrigated rice

systems in the Sahel zone of West Africa. Average grain yields were

4.1–5.6 Mg ha�1 vis‐a‐vis the simulated potential yields of 8.0–10.0 Mg ha�1

for the Senegal River Valley (Table XII). An estimated 46–70% of the applied

N is lost from the soil‐plant‐water system due to variable rates and poor timing

of N application (Haefele and Wopereis, 2004).

Haefele and Wopereis (2004) improved irrigated rice fertilizer recommen-

dations for five AEZs of the Senegal River Valley, based on a simple three‐quadrant model, farmer surveys, on‐station experiments, and simulated

potential yield for the WS and DS. The blanket recommendation of

120‐26‐50 kg ha�1 of N‐P‐K for all five AEZs was changed to 161‐20‐0 kg ha�1

(AEZ I, II) and 135‐20‐0 kg ha�1 (AEZ III, IV, V) for the WS. For the DS,

they recommended 187‐25‐0 kg ha�1 (AEZ I), 161‐20‐0 kg ha�1 (AEZ II),

and 135‐20‐0 kg ha�1 (AEZ III); no DS recommendations were derived for

AEZ IV because of a lack of weather data and for AEZ V because of low‐yield potential in the DS. These AEZ‐based fertilizer recommendations were

embedded into ICM recommendations, with emphasis on weed control and

soil fertility management. In addition to optimum fertilizer use, the selection

of nutrient‐eYcient rice varieties, adequate radiation and temperature, good

water control, and optimum crop management are critical to maximize rice

yields and nutrient‐use eYciency (Balasubramanian et al., 2004).

Table XI

Forms in Soils, Sources, Critical Values for Deficiency and Toxicity, and Application Methods for Essential Nutrients in Rice Cropping

Nutrientsa Occurrence in soil

Critical value:

deficiency Critical value: toxicity Nutrient sourcesb Methods of applicationc

N NH4þ, NO3

�; organicmatter

1.4‐mg m�2 leaf area – Urea, DAP, AS, CAN,

coated urea; organic/

green manures

Soil two to four splits; LCC

based; deep placement;

0.5% urea spray

P Solution P $ Labile

P $ Nonlabile P;

organic P

Bray‐1 P: 7 mg kg�1

soil; Olson‐P:5 mg kg�1 soil

Excess P induces Zn

deficiency in basic soils

Rock‐ or single/double/triple super‐phosphate,DAP

Basal, seedling root‐dippingin soil‐P slurry; OPM‐/APM‐based rates

K Solution K $ Ex.

K $ Non‐ex.K $ Mineral K;

organic K

Ammonium acetate‐K:

20‐cmol kg�1 soil

– KCl, straw or straw

compost

Basal at low yield level; two

splits at high yield level;

OPM‐/APM‐based rates

S SO42�, S�, elemental S;

organic S

Ca(H2PO4)2 S: 9‐mg

kg�1 soil (combined

w/Zn deficiency in low

OM, high‐allophanematerials and oxides,

and sandy soils)

>0.07 mg liter�1 of H2S

(mainly in sandy, peat,

and acid sulfate soils)

Rain or irrigation water;

AS, single super‐phosphate; gypsum,

elemental S

Soil application of

S‐containing materials

Zn Zn in clay minerals;

ZnS; Zn adsorbed

on amorphous

oxides and

mg‐carbonates;humic Zn

1‐N NH4‐acetate (pH4.8)‐Zn: 0.6‐mg kg�1

soil; 0.05‐N HCl‐Zn:1.0‐mg kg�1 soil

Nil ZnSO4, ZnO 25‐kg ha�1 ZnSO4 applied

on soil surface/

floodwater; seedling

root‐dipping in 2% ZnO

solution

Fe Fe3þ, Fe2þ 2 mg liter�1 (dryland

rice only)

300‐mg liter�1 Fe2þ

(aggravated by poor

supply of K, P, Zn)

Fe‐sulfate, Fe‐citrate Foliar spray of 0.1–0.5%

solution; apply fast‐decomposing GM

(continued)

INCREASIN

GRIC

EPRODUCTIO

NIN

SUB‐SAHARAN

AFRIC

A103

Table XI (continued)

Nutrientsa Occurrence in soil

Critical value:

deficiency Critical value: toxicity Nutrient sourcesb Methods of applicationc

Mn Acid soil: 10‐ to 100‐mg

liter�1 Mn2þ in soil

solution; Calcareous:

0.5‐mg liter�1 Mn2þ

DTPA þ CaCl2‐Mn:

<1 mg liter�1

>100‐mg liter�1 Mn2þ Mn‐oxide (flooded rice);

Mn‐sulfate (dryland rice)

Soil; foliar spray; soaking

of seeds in Mn solution

Cu Cu‐oxides, carbonates,silicates, and sulfides;

chelated‐Cu

0.05‐N HCl‐Cu:0.1‐mg kg�1 soil

(mostly in peat soils)

– Cu2O, CuSO4 Soil or spray application of

Cu2O or CuSO4 once

in 3 years

Mo Mo on silicates;

Mo‐sesquioxides;organic Mo; MoO4

2�

soluble ions

0.15‐mg liter�1 soil

solution (rarely

deficient)

– Ammonium molybdate Rarely applied for rice

B H3BO3 or borates;

B‐sesquioxide andillite/vermi‐culiteclay; organic B

Hot water‐B:0.5‐mg kg�1 soil

(rarely deficient)

>5‐mg kg�1 soil (only in

saline, alkaline soils)

B‐rich groundwater

(>2 mg B liter�1);

borates

Rarely applied for rice

(applied for wheat in

rotation with rice)

Si Silicates; clay minerals mainly in acid

sandy soils

– Burnt rice hull; silicates Soil application

aN, nitrogen; P, phosphorus; K, potassium; S, sulfur; Zn, zinc; Fe, iron; Mn, manganese; Cu, copper; Mo, molybdenum; B, boron; Si, silica.bAS, ammonium sulfate; CAN, calcium ammonium nitrate; DAP, diammonium phosphate; KCl, potassium chloride (muriate of potash); rock‐P, rock‐phosphate.cAPM, addition plot method; LCC, leaf color chart; OPM, omission plot method.

Information sources: Balasubramanian et al. (1999), Diamond (1985), Dobermann and Fairhurst (2000), Dobermann et al. (2004), Fairhurst and Witt

(2002), and Neue and Mamaril (1985).

104V.BALASUBRAMANIA

NETAL.

Table XII

Indigenous N Supply, Applied Fertilizer Rates, Grain Yield, and N Recovery EYciency

of Irrigated Rice in Farmers’ Fields in the Senegal River Delta of West Africa,

Based on Field Surveys 1995–1997

Parameter

Sites

Tiagar 1,

Senegal

Tiagar 2,

Senegal

Guede,

Senegal

Location,

Mauritania

Season (WS)a 1995b 1995c 1996 1997

No. of cases 10 10 20 37

Mean INSd 72 60 31 32

Applied N (kg ha�1) 101 80 117 115

Applied P (kg ha�1) 22 15 21 20

Applied K (kg ha�1) 0 7 0 0

Grain yield (Mg ha�1) 4.9 4.1 5.6 4.4

RENe (%) 30 38 44 33

aWS, wet season.bSingle‐rice cropping.cDouble‐rice cropping.dINS, indigenous N supply.eREN, recovery eYciency of applied N (% of applied N recovered in grain þ straw).

Adapted from Haefele and Wopereis (2004).


For irrigated wetlands with adverse soil conditions such as salinity, alka-

linity, acidity, or Fe and Al toxicity, an integrated approach is needed—by

combining resistant or tolerant rice varieties with balanced plant nutrition

and crop management. For example, ridge planting of rice and the applica-

tion of balanced (N, P, K, Zn) fertilizers can reduce Fe toxicity significantly in

the poorly drained wetlands of rainforests andGuinea savanna zones ofWest

and Central Africa (Sahrawat, 2004a). In semiarid areas, the salinity problem

can be tackled by planting salt‐tolerant rice varieties and applying a full dose

of recommended fertilizers (WARDA, 2002).

2. Toposequence‐Based Nutrient Management in an Inland Valley

Soil fertility problems vary according to position along the inland valley

toposequence. For coarse infertile soils in the upper and middle parts, ferti-

lizers must be combined with soil amendments such as composts, manure, or

rock‐P to optimize rice yields and nutrient‐use eYciency. On the other hand,

soils in the valley bottom are relatively high in clay and OM contents and

water‐holding capacity, but poor in P and N; therefore, they generally

respond to P and N fertilizers, with less additional response to soil amend-

ments. For example, in an inland valley of theGambia, Jobe (2003) noted that


rice responded mainly to fertilizers but not to soil amendments such as

manure, rock‐P, and phosphogypsum in the valley bottom, whereas rice in

the upper and middle parts benefited most from the application of 50% of

recommended nutrients through fertilizers and the rest through 4Mg ha�1 of

animal manure. Thus, the combined use of organic and inorganic sources

of nutrients is recommended by the ISFM strategy to maximize cereal yields,

especially in nutrient‐poor soils of the upper reaches (Vanlauwe et al., 2002).

3. Site‐Specific Nutrient Management

In Asia, a strategy called SSNM has been developed for precision nutrient

management in irrigated rice (Buresh et al., 2003; Dobermann et al., 2004).

SSNM provides an approach for ‘‘feeding’’ rice crops with nutrients as and

when needed. Farmers dynamically adjust the application and management

of nutrients to crop needs according to location and season. SSNM advocates

� The optimal use of existing indigenous nutrient sources, including crop

residues and manures

� Timely fertilizer application to meet the deficit between rice demand for

nutrients and the supply of nutrients from soil and organic inputs (Fig. 8).

In SSNM, the leaf color chart (LCC) is used to apply N fertilizer as

per the crop’s need during the growing season (real time N management)

(Balasubramanian, 2004; Shukla et al., 2004). Rice leaf color is monitored in

the field with an LCC from 15 days after transplanting to the booting stage

at 7‐ to 10‐day intervals, and N fertilizer is applied whenever the leaf color

falls below the chosen critical value.

Figure 8 SSNM approach: ‘‘apply fertilizers as and when needed to fill the deficit between

crop need and indigenous nutrient supply’’ (source: Buresh et al., 2003).


An omission plot technique is used for crop need‐based P and K applica-

tion. A P‐omission plot—a plot with no added P and the full rate of other

nutrients—visually demonstrates to farmers the deficit of P. Similarly, a

K‐omission plot—a plot with no added K and the full rate of other nutri-

ents—demonstrates the deficit of K (Buresh et al., 2003; Dobermann et al.,

2004). The diVerence in grain yield between a nutrient‐omission plot and a

full NPK plot is used to make P and K recommendations, using the formula:

‘‘To produce one metric ton of paddy over the yield of the nutrient omission

plot, farmers should apply 15‐ to 20‐kg P2O5 and 30‐kg K2O per ha’’

(Balasubramanian et al., 2003).

Other nutrients such as S and Zn are applied as per local recommendations

at sites deficient in such elements.

E. WATER MANAGEMENT FOR RAINFED AND IRRIGATED AREAS

1. Managing Water for Rainfed Rice Farming

Water is the single most critical constraint in rainfed rice farming. For all

rice varieties, the water requirement is the highest during the reproductive

phase, that is, from PI to heading; therefore, during this period, rice fields

must have enough soil moisture in rainfed drylands or standing water (about

0.05‐m depth) in rainfed or irrigated wetlands. Any moisture deficit (due to

drought) at this critical period will seriously aVect spikelet formation and

grain filling, with drastic reductions in yield or complete crop failure.

For drylands and rainfed wetlands, management options are needed to

tackle extreme drought and flood events. First, the duration of rice varieties

must be matched with the duration of the wet period of the growing season.

Second, the planting date is adjusted in such a way that rainfall is adequate

during the period of maximum water requirement (PI to heading). Third,

minimum tillage and mulching can be practiced in drylands to conserve

moisture at critical periods or to overcome unexpected dry spells (Hatibu

et al., 2000; WARDA, 2002).

RWH is defined as ‘‘concentrating, collecting, and storing rainwater for

diVerent uses at a later time in the same area where the rain falls, or in

another area during the same or later time’’ (Hatibu, 2000). There are two

types of RWH: (1) in situ RWH where rain is captured where it falls and

(2) micro‐ and macrocatchment RWH where the runoV from the catchment

area is collected and stored for use in the same or downstream areas during

the same or later time. Building farm ponds, small reservoirs, or earth dams

across water courses is necessary to store peak floods (Hatibu et al., 2000).

RWH and the development of microcatchment storage structures must be

given top priority in drought‐ and flood‐prone rainfed wetlands. Water from


farm ponds can be used to provide 1–2 life‐saving irrigations during periods

of drought at critical stages to increase and stabilize rice yields. Once

supplementary irrigation is available, farmers will tend to apply additional

inputs to enhance rice productivity with reduced risks. In addition, farm

ponds will help recharge groundwater in the vicinity, which in turn will

revive rainfall‐dependent streams and increase water availability in rural

areas. If enough pond water is available in the DS, farmers can diversify

into growing small plots of vegetables or other cash crops to diversify their

income sources and improve their diets. Further diversification into poultry

and livestock is possible if enough water is available to take care of them.

Farm ponds can also be used to grow fish.

In flood‐prone areas, using reservoirs to store and regulate flash floods

can minimize crop damage due to sudden floods (Hatibu et al., 2000).

In addition, the provision of drainage is critical to reduce Fe toxicity and

stabilize rice production. It is diYcult to drain fields during periods of

heavy rains. At other times, farmers are reluctant to drain their rice fields

for fear of losing applied N, worries about the arrival of the next rain to

reflood their fields, and increased weed infestation under nonflooded condi-

tions. In saline and mangrove swamps, ridge planting is recommended to

improve drainage and reduce the adverse eVect of excess Fe and Al and salt

(WARDA, 2002).

Developing stress‐tolerant rice varieties will help increase and stabilize

rice yields in poorly drained wetlands with problem soils. IRRI has devel-

oped a breeding line (IR73678‐6‐9‐B) derived form O. sativa cv IR64 �O. rufipogon that can tolerate acid sulfate conditions in coastal wetlands;

Vietnam released it as national variety AS‐996 in 2002. It can be evaluated in

acid sulfate soils of Africa. Genes have been tagged for submergence toler-

ance (Sub1A) (Xu et al., 2006) and other abiotic stresses (Table IX) for

incorporation into popular varieties (Gregorio et al., 2006).

2. Water Use and Water Productivity in Irrigated Rice Systems

Irrigation is the best means of increasing rice production with modern

varieties. Improved water conveyance at the systems level and judicious

water use at the farm level are critical to derive maximum benefits from

irrigation schemes.

Large irrigation projects, especially those in the public sector, have often

failed in Africa because of several factors: the lack of a well developed and

coherent irrigation subsector policy and strategy; high capital and operating

costs (especially for irrigation schemes based on pumping); poor cost‐recoveryand lack of funds for management; poor operation, repair, and maintenance


of irrigation infrastructure; inadequate farm support services; poor ownership

by users; and low economic viability (FAO‐Aquastat, 2005). Owing to inade-

quate drainage, salinity and alkalinity have developed in many irrigated areas

in the semiarid savanna, Sudan, and Sahel zones of West Africa (Massoud,

1977; WARDA, 1999). Large investments needed to rehabilitate such irriga-

tion schemes and to improve systems level water delivery may not be available

from governments. This is where strong public–private partnerships need to

be developed to encourage initial investments in reconstructing irrigation

infrastructure and providing processing and marketing facilities for the

commercialization of irrigated rice production.

Farmer‐controlled tube‐well irrigation systems are highly successful in

Asia (e.g., in Bangladesh) (Hossain et al., 2006). Such small irrigation

schemes have been developed for rice cultivation in the high‐altitude marsh-

lands of Rwanda and Burundi. It is predicted that Africa will have more

small‐scale irrigation schemes in the next 25 years. The development of small

irrigation schemes, the construction of related rural infrastructure, and the

formation of viable water‐user associations must go hand‐in‐hand to realize

the full potential of these irrigation projects and to improve farmers’ liveli-

hood. In addition, both land and water managements must be integrated to

maintain productivity at a high level and environmental quality at an

acceptable level. We need to consider cropping systems instead of individual

crops for enhancing water productivity. Barker et al. (1998) show how

diVerent practices reduce various components of water losses in irrigated

rice systems (Table XIII).

Salinity management is critical for improving the productivity of irrigated

rice in semiarid areas of West Africa. Among the management practices that

minimize salinity problems, crop selection and rotations, land leveling, and

salt leaching have long‐term eVects, while tillage, fallowing and mulching,

landform and planting method, and the application of manures, fertilizers,

and amendments have only a short‐term eVect (Massoud, 1977). Crops such

as rice that require frequent irrigation can reduce salinity eVectively if

adequate drainage is available. With land leveling and tillage, precautions

must be taken not to bring a salt layer, if present, to the crop root zone; any

tillage that improves internal drainage will help reduce salt accumulation.

Evaporation from exposed soil surface during fallow periods will lead to salt

accumulation, and, in this case, mulching can reduce evaporation and

thus salt accumulation on the surface. Although the application of organic

residues and manures improves soil physical and chemical properties, they

carry some salts with them. Proper fertilizer use will not aVect salinity.

Amendments are added mainly to sodic soils to reduce the exchangeable

sodium percentage and improve permeability and drainage (Massoud, 1977).

In addition, eVective management of waste water and saline water for

irrigation is also important.

Table XIII

Practices for Increasing Water Productivity in Irrigated Rice Farming

Practice Ta Eb S&Pc SROd RCLe

Improved short‐duration rice varieties þImproved agronomic management þChanging schedules to reduce evaporation þReducing water for land preparation þ þ þChanging rice planting practices þ þ þReducing crop growth water þ þ þMaking more eVective use of rainfall þ þWater distribution strategies þ þ þWater recycling and conjunctive use þaT, transpiration.bE, evaporation.cS&P, seepage and percolation.dSRO, surface runoV.eRCL, recycled water use.

Adapted from Barker et al. (1998).


Among the water‐saving technologies, intermittent irrigation or alterna-

tive wetting and drying (AWD) is the most promising because it oVers highwater productivity coupled with a low penalty on grain yield. In China and

the Philippines, AWD is reported to save from 13 to 30% of irrigation water

at the field level, with no significant reduction in yield (Cabangon et al.,

2001).

The development of rice varieties with short duration, early seedling vigor,

and tolerance of submergence will increase water‐use eYciency. Several

medium‐duration (120–130 days) high‐yielding rice varieties are available

for irrigated wetlands: BG 90‐2 and 380‐2; BKN 7033 and 7167; BR

51‐46‐5; IR8, 22, 46, 54, 58, and 841; ITA 123; Sahel 108, 201, and 202;

TOX 728‐1; and WITA 1, 3, and 7. However, improved very early maturing

rice varieties are needed for irrigated lands in northern Guinea, Sudan

savanna, and Sahel zones and early maturing and Fe toxicity‐tolerant vari-eties for irrigated rice in rainforest zones of SSA (WARDA, 2002). In Asia,

hybrid rice varieties were found to be more adapted to water‐deficit condi-tions because of their early seedling vigor and vigorous root system that favor

the eYcient use of available water (Virmani, 1996). But suitable hybrid rice

varieties have yet to be developed for SSA. Salinity‐tolerant high‐yieldingvarieties such as ITA 212 (FARO 35) and ITA 222 (FARO 36) are available

for irrigated areas with saline soils.

Aerobic rice is another alternative for water‐deficit areas (Atlin, 2005); in

this system, aerobic rice varieties grow in nonflooded soils and yield as high


as 5–6 Mg ha�1, using 40–50% less water than flooded rice systems. Water

productivity was as high as 0.6–0.8 g grain kg�1 water for aerobic rice

varieties in North China (Yang et al., 2005). Promising aerobic rice varieties

are Apo and Magat for the Philippines (Bouman et al., 2005) and HD 502

and HD 297 for China (Bouman et al., 2006). Research is ongoing for

further improvement of rice varieties, crop and water management, and

sustainability for aerobic rice systems. In SSA, aerobic rice varieties can be

tried in water‐deficit irrigated areas or rainfed wetlands where supplementary

irrigation is available.

F. WEEDS, INSECT PESTS, AND DISEASES AND THEIR MANAGEMENT

1. Weeds, Their Management, and Their Multiple Uses

Weeds are plants out of place. They are the most serious biological

constraint to rice production in SSA (Johnson, 1997). The major rice‐fieldweeds that occur in SSA are listed in Table XIV.

Weed infestation is serious wherever water control is poor as in most

rainfed and poorly managed irrigated areas. Improper land preparation and

poor leveling lead to poor spread of water and more weeds in irrigated rice

fields. Becker and Johnson (1999) observed that Echinochloa species are the

most common weeds in fully irrigated systems and Panicum laxum in poorly

irrigated fields in West Africa. More weeds germinate and compete with rice

under direct seeding than in transplanting conditions (Balasubramanian and

Hill, 2002). When soil is depleted with reduced fallow periods, weeds become

more competitive than rice, especially in drylands. The parasitic weed, Striga

spp. (S. aspera and S. hermonthica), is a major problem in dryland rice

mainly in the savanna zone but not in the forest zone (Adagba et al., 2002).

Rice yield loss due to weeds can be as high as 25–40%, with total crop loss

in extreme cases (WARDA, 1998). Manual weeding is the most common, as

herbicides are beyond the reach of poor farmers and, hence, basically

suitable for the low‐income countries of SSA. In direct‐seeded irrigated

rice trials in the Senegal River delta, weeds had to be controlled until

32 days after seeding (DAS) in the WS and 83 DAS in the DS to get 95%

of the rice yield of weed‐free fields (Johnson et al., 2004). Manual weeding,

however, is time‐consuming and labor‐intensive. An estimated 27–37%

of the total labor input goes for weeding alone (WARDA, 1998). However,

timely hand weeding not only controlled weeds eVectively but also

maintained higher levels of pest predators such as spiders and beetles in

rice fields than in herbicide‐treated plots. Placing the uprooted weeds in piles

within rice fields resulted in larger populations of spiders than any other

method of weed disposal, including removal from fields (Afun et al., 2000).

Table XIV

Major Rice‐Field Weeds Reported from Africaa

Grasses Sedges Broad‐leaf typesParasitic

(dryland rice)

Cynodon dactylon Cyperus diVormis Alternanthera sessilis (L.) Striga asiatica

(L.) Pers.,

Dactyloctenium

aegyptium (L.) Willd.,

Digitaria spp.,

Echinochloa crus‐galli(L.) P. Beauv., E.

colona (L.) Link., E.

stagnina (Retz.) P.

Beauv., E. pyramidalis

L., Eleusine indica (L.)

Gaertn., Imperata

cylindrica (L.)

Raeuschel, Ischaemum

rugosum Salisb.,

Leersia hexandra Sw.,

Oryza sativa (red rice)

(L.), Panicum repens

L., Panicum laxum

Sw., Paspalum

scrobiculatum L.,

P. polystachum R. Br.,

Rottboellia

cochinchinensis

(Lour.) Clayton,

R. exaltata, Setaria

pumila (L.) P. Beauv.,

Spermacoce ruelliae

L., C. happen L.,

C. iria L.,

Fimbristylis

ferruginea (L.)

Vahl., F. pilosa

(L.) Vahl., Pycreus

macrostachyos,

Kyllinga

squamulata

(Thon),

Abildgaardia

hispidula

R. Br. ex DC.,

Aeschynomene indica

L., Ageratum

conyzoides L.,

Amaranthus spinosus L.,

Ammania baccifera L.,

Commelina benghalensis

L., C. diVusa Burm. f.,

Euphorbia heterophylla

L., Diplazium sammatii

(Kuhn), Eclypta

prostrata (L.) L.,

Ludwigia octovalvis

(Jacq.), Trianthema

portulacastrum L.,

Portulaca oleracea L.,

Zaleya pentandra L.

L. Kuntze, Striga

aspera (Willd.)

Benth.

aData sources: Adagba et al. (2002), Johnson (1997), and Rao et al. (2007).


Developing weed‐competitive rice varieties is one strategy for cost‐eYcient weed control in rice crops. In West Africa, O. glaberrima was

found to be more tolerant of Striga (WARDA, 1998) and other weeds

(Johnson et al., 1998) than O. sativa. As discussed earlier, the dryland

NERICA (a cross between O. glaberrima and O. sativa) varieties are highly

competitive with weeds due to their early seedling vigor, fast canopy devel-

opment, and droopy lower leaves that shade out weeds (Futakuchi and

Jones, 2005; Haefele et al., 2004; WARDA, 2003–2004). The newly devel-

oped wetland NERICA varieties have weed‐suppressing ability similar to

that of their dryland counterparts (WARDA, 2003–2004, 2004–2005). The

second strategy is planted legume fallows, which are reported to smother


weeds and fix N for the following rice crops. The rice–legume fallow rotation

was more productive than the rice–natural fallow rotation (Akanvou et al.,

2001a; Carsky et al., 2001; WARDA, 1998). The third strategy of rice seed

priming for fast germination and early canopy development in dry direct‐seeded rice and their eVect on weed suppression is yet to be assessed in the

field (WARDA, 1998).

Although weeds compete with rice crops, some of them are useful to

subsistence farmers. For example, weeds such as Echinochloa colona and

E. pyramidalis have multiple uses as fodder, thatching material, and grains;

Paspalum scrobiculatum as fodder, poisonous raw grains, and medicine

(Burkhill, 1994); Setaria pumila as fodder and thatching material; Tri-

anthema portulacastrum as food and medicine; and Zaleya pentandra as

fodder for horses and donkeys (Burkhill, 1985). Other rice‐field weeds such

as Rottboellia exaltata and Spermacoce ruelliae provide fodder or grazing

matter for livestock.

2. Major Insect Pests and Diseases and Their Management

Pink stem borer (Sesamia calamistis) is the main pest of dryland rice,

whereas AfRGM (Orsylia oryzivora) is common in rainfed and irrigated

wetlands. Other pests are striped (Chilo zacconius), white (Maliarpha spp.),

and yellow (Scirpophaga spp.) borers and stalk‐eyed fly (Diopsis macro-

phthalma); grain‐sucking bugs (Aspavia sp., Stenocoris claviformis); case

worm (Nymphula depunctalis); and whorl maggot (Hydrellia sp.) (John

et al., 1986; WARDA, 2002). Incidence of stem borers and stalk‐eyed fly is

severe in all humid and dry zones, while that of grain‐sucking bugs, case

worm, whorl maggot, and AfRGM is more severe in humid forest and

Guinea savanna zones than in the Sudan savanna zone (John et al., 1986).

The major diseases of rice in Africa are blast (caused by Pyricularia oryzae),

glume discoloration (fungal complex: caused by Sarocladium sp. and

Curuvularia sp.), RYMV, sheath rot (caused by Sarocladium sp.), leaf scald

(caused by Rhyncosporium oryzae), sheath blight (caused by Thanetophorus

cucumeris), and bacterial leaf blight (caused by Xanthomonas campestris pv.

oryzae) (John et al., 1986; WARDA, 2002). Other pests such as rodents and

birds attack rice in all ecosystems. Nematodes and termites are a serious

problem in dryland rice in some areas.

Integrated pest management (IPM) is a decision‐support system for the

selection and use of pest control strategies that minimize dependence on

chemical pesticides and improve human health and environmental quality.

Growing a healthy crop is the key to good IPM. Other IPM technologies

for rice are: (1) deployment of pest‐resistant varieties, (2) no early spraying

against leaf folders and thrips, (3) an active barrier system for rat control,


(4) silica application for blast control, and (5) timely and judicious use

of fast‐acting bio or synthetic pesticides when pest infestation is serious,

threatening the crops.

Developing resistant varieties has been the main focus of research at

WARDA. Two rice varieties, WITA 8 and WITA 9 (WARDA, 2002), and

three wetland NERICAs have been selected for resistance to RYMV

(WARDA, 2003–2004, 2004–2005). Breeders employ biotechnology tools

to incorporate specific genes into high‐yielding rice varieties to make them

resistant to or tolerant of various pests and diseases. For example, two

brown planthopper (BPH ) genes for BPH, six Gm genes for gall midge,

eight Xa genes for bacterial blight, and eight Pi genes for blast have been

tagged at IRRI for incorporation into high‐yielding rice varieties through

MAS. Similar work is ongoing at WARDA to identify and tag resistance

genes from cultivated and wild rice species to deploy against Africa‐specificinsect pests and diseases.

G. GRAIN QUALITY MANAGEMENT: FROM BREEDING TO MILLING

As early as 1985, Buddenhagen (1986) pointed out the importance of

having good grain quality for local rice in Africa. He gave four reasons:

� Rice consumers, especially in urban areas, used to high‐quality and low‐costimported rice will demand the same level of quality and cost‐eVectivenessfrom local rice markets

� The earlier introduced rice varieties in the Sahel of West Africa were high‐quality, long‐grain rice varieties from Southeast Asia

� Although poorly milled and maybe not of long‐grain type, many of the old

land races of West and East Africa have very good taste (some with good

aroma) and cooking quality preferred by local consumers

� African rice traders are as sophisticated as any in the world to exploit

consumer preferences for quality rice.

Buddenhagen (1986) recommended the breeding of medium‐grain types

with good taste and cooking quality such as Sierra Leone’s Ngovie or LAC

23, or Tanzania’s aromatic rice for rainfed drylands and wetlands, and long‐grain types for irrigated rice in SSA. Proper plant nutrition and good water

and pest control during crop growth are important for producing healthy,

well‐filled grains.

Rice farmers in Africa lose 15–50% of the market value of grains because

of improper handling of rice during and after harvest. To reduce grain losses

andmaintain grain quality, rice must be harvested immediately after maturity

(95% mature), threshed soon after harvest, cleaned, and dried to <14%

moisture content (MC). Simple dryers and sealed storage options are


available for drying and storing the grain properly. Airtight storage is recom-

mended to kill storage pests without pesticides, preserve grain quality, and

maintain seed viability. Rice must be milled at 12–14% MC depending on

grain types in modern mills to maximize head‐rice recovery. IRRI has devel-

oped appropriate and cost‐eVective tools such as a low‐cost moisture meter to

monitor grain moisture while processing, super bags for sealed grain storage,

a rice‐milling chart to guide optimum milling of rice, and a portable grain

quality test kit (IRRI, 2005). An improvement in harvest and postharvest

processing will enhance the market value of rice and thus not only improve

farmers’ income and livelihood but also enhance profit to millers.

H. DIVERSIFICATION OF RICE FARMING SYSTEMS

Generally, rice is not highly profitable in many areas. However, in the

WS, rice is the most suitable crop for wetlands. In the DS, dryland crops

such as grain legumes, vegetables, onion, garlic, watermelon, and cotton

are grown in Asia and Africa to enhance farmers’ income. In a 5‐year(1996–2001) crop rotation trial in the Accra Plain of Ghana, Nyalemegbe

et al. (2003) found that rice–vegetable (rice–okra and rice–eggplant) systems

are more profitable than rice–rice, rice–cowpea, or rice–watermelon systems.

Vegetable yields were low but the prices were high in the DS and vice versa in

the WS. In this study, deep‐rooted crops such as okra and eggplant tapped

nutrients from the subsoil, aerated the soil, and added OM to the system,

while grain legumes such as cowpea fixed N and added crop residues to

improve soil fertility. The rice–rice system reduced sedges considerably, but

not the grasses, due to continuous submergence, while the rice–cowpea

and rice–okra systems reduced noxious water‐loving grass weeds such as

E. crus‐galli and Ischaemum rugosum.

Crop‐livestock integration with a cut‐and‐carry fodder system will

improve cash flow and generate income for dryland farmers (Otsuka and

Yamano, 2005). This system will also improve the use of crop residues as

fodder for animals and animal manure to improve soil fertility in rice fields.

I. ICM FOR RICE

In the literature, there is no universal definition of ICM. In practical terms,

it means good agronomy or good crop management. We use the ICM

approach to promote the combined use of adapted rice varieties and

location‐specific crop management technologies to increase land and water

productivity and profit to farmers in irrigated rice farming (Balasubramanian

et al., 2005; Chandrasekaran et al., 2004). From 2004, the FAO of the United


Nations has adopted the ICM approach to identify and deploy technologies

for increasing rice productivity in Asia and elsewhere.

ICM has two sets of options: core and location specific. Core options are

those that perform similarly in multiple locations, for example a locally

adapted variety, good‐quality seed, robust young seedlings, crop need‐based nutrient application, and IPM. Location‐specific options are those

that perform diVerently at diVerent locations or that can be practiced only in

certain locations; plant spacing, intermittent irrigation, the use of organic

manure, and so on are location specific. Both types of ICM options have to

be selected to meet farmers’ needs in each location; they must also be

updated periodically to incorporate new research findings as they become

available. Additionally, timely harvest and threshing, proper cleaning and

drying of grain to 14% MC, the use of sealed storage systems, and proper

milling with the help of a rice‐milling chart will reduce grain losses and

increase the market value of milled rice.

Key components of ICM successfully validated in Asia are: (1) the selec-

tion of locally adapted rice varieties, (2) the use of good‐quality seed at low

seed rates, (3) the preparation and planting of young seedlings at the four‐leafstage, (4) transplanting of 1–2 young seedlings per hill in a square pattern

(0.2 m � 0.2 m to 0.25 m � 0.25 m), (5) 2–3 mechanical weedings þ soil

stirring at 10‐day intervals from 15 days after transplanting, (6) intermittent

irrigation during vegetative and grain‐maturing phases and continuous shal-

low flooding from PI to flowering, (7) crop need‐based nutrient management

(SSNM), and (8) IPM.

ICM pilot studies conducted in Asia during 2000–2004 demonstrated that

ICM fields produced 1.1–2.5 Mg ha�1 more rice yield than rice crops under

recommended conventional practices; additional profit due to ICM ranged

from US$115 to US$265 ha�1 per season (Balasubramanian et al., 2005).

Growing healthy crops through ICM will also help reduce pesticide use and

pesticide‐related health risks to farmers. ICM will be especially beneficial to

smallholders with limited land and suYcient labor. Seed producers will

benefit more than grain producers when they adopt the ICM approach.

ICM for irrigated rice in West Africa focuses on land preparation, seed

rates and sowing time, cultivar choice, and crop establishment techniques,

and provides a farming calendar for a given combination of site, sowing

date, cultivar choice, and crop establishment technique (WARDA, 2000).

Additional ICM options are fertilizer rates for specific target yields, weed

and water management techniques, and postharvest techniques (Defoer

et al., 2002). In on‐farm evaluations in Senegal and Mauritania, mean rice

yield increased from 3.8 Mg ha�1 for the farmers’ practice to 5.5 Mg ha�1 for

ICM plots and the average net benefit rose from US$215 to US$525 ha�1,

despite the slightly increased cost for ICM plots. Moreover, the adoption of

ICM options tends to reduce risks (Haefele et al., 2000). The ICM options


most attractive to farmers were improved fertilizer and weed management,

adapted high‐yielding varieties, and mechanized harvesting and postharvest

technologies. Adding proper land leveling; the preparing and planting

of young, vigorous seedlings; intermittent irrigation with soil stirring; and

improved postharvest management to rice‐ICM recommendations in SSA

may further enhance rice yields and profitability to African farmers, as

evidenced in Asia (Balasubramanian et al., 2005). The available best manage-

ment technologies for rice in diVerent ecosystems of SSA are listed in

Table XV. These technologies can be deployed as a basket of options to

farmers using the ICM approach.

VIII. RICE INTENSIFICATION ISSUES ANDTHOUGHTS FOR THE FUTURE

A. RICE INTENSIFICATION IN RELATION TO VECTOR‐BORNE

HUMAN DISEASES

Farmers consider flooded wetland rice cultivation risky for health reasons—

the fear of contracting wetland‐related human diseases such as malaria

and bilharzia. The distribution of these two diseases in diVerent countries ofSSA is shown in Table V.

Malaria caused by mosquitoes (Anopheles gambiae s.l.) is the single

biggest killer disease in SSA; about half a million children die of malaria

ever year. The severity of malaria incidence depends on the susceptibility of

local people and the preventive measures they use. Research findings indi-

cate that the expansion of rice cultivation to a new area or conversion of

single‐rice to double‐rice cropping will not further increase the incidence of

malaria in the already endemic humid and savanna zones. However, in new

irrigation schemes or with the expansion of existing irrigation schemes to

new areas in the Sahel, the risk of malaria may increase in the short term as

new people and laborers settle the area. As the settlers acquire immunity, the

danger of malaria goes down steeply (WARDA, 1996).

Of the more than 200 million people infected by bilharzia or schistoso-

miasis worldwide, about 10% of them are seriously incapacitated—80% of

which are in SSA. The disease is caused by worms known as schistosomes—

urinogenital schistosomiasis by Schistosoma haematobium and intestinal

schistosomiasis by S. mansoni. Aquatic snails and humans provide alternative

hosts for the worms. The disease is prevalent where people are in contact

with snail‐infested water—slow‐moving rivers and streams and vegetation

banks of lakes. Preventive health measures such as the use of boots and the

destruction of snail‐infested floating vegetation as well as timely treatment of

Table XV

Available Best Management Technologies for Rice in DiVerent Ecosystems of SSA

Practice

Irrigated

Rainfed wetland Mangrove swamps DrylandTransplanted Direct seeded

Variety Short‐duration high‐yielding varieties;

salt‐tolerant forsaline areas

Weed competitive,

early vigor, fast

canopy

development,

nonlodging

Short duration, weed

competitive,

drought‐ and flood‐tolerant

Tolerant of Fe and

Al toxicity,

submergence,

salinity

Weed competitive,

acid‐tolerant, andP‐eYcient

Seed quality Good seed (certified) Good, primed seed

Nursery Good seedbed and

thin sowing

– Good seedbed and thin

sowing

Good seedbed and

thin sowing

–

Seedling quality Young, robust (four‐leaf stage)

– Young, robust, tall Robust, healthy –

Seed rate (kg ha�1)a 20–30 60–80 20–30 for TPR and

60–80 for DSR

20–30 60–100

Landform Good puddling and

leveling

Plowing or puddling

and leveling

Plowing or puddling

and leveling

Plowing, forming

ridges

Plowing, leveling, or

terracing

Planting Two to three seedlings

per hill at 0.2 m �0.2 m spacing

Broadcast or row‐seeded on puddled

or moist soil

Transplanted or

broadcast or row‐seeded on wet soil

Transplanted on

ridges with two to

three rows per

ridge

Broadcast, drilled in

rows, or dibbled

Water/irrigation

managementbIntermittent irrigation

up to PI and then

after flowering;

0.05‐m water level

from PI to flowering

Saturated soil first 10

days; then

intermittent up to PI

and after flowering;

0.05‐m flood from

PI to flowering

Rainwater harvesting

and farm pond,

reservoir, earth dam;

one to two life‐saving irrigations at

critical stages

Good drainage to

mitigate tidal

flooding; ridges to

facilitate drainage

Terracing on slopes;

mulching to

conserve moisture;

contour live

hedges

118V.BALASUBRAMANIA

NETAL.

Nutrient

management

Crop need‐based SSNM; adequate P in saline

soils; S and Zn in deficient soils

Ecosystem and

toposequence based

for wetland rice

Ecosystem based for

mangrove swamps

P before N; rock‐P to

legume fallows,

then rice

Weed control Herbicide, manual Herbicide, manual;

weed‐competitive

variety

Weed‐competitive

variety; manual

weeding

Manual, timely

weeding

Weed‐competitive

variety; mulching;

manual weeding

Pest controlc Resistant variety, IPM

Mechanization Animal power and two‐wheel tractor for land preparation; simple manual seeders; rotating hoes for weeding; simple threshers

and cleaners

Preharvest Drain 2 weeks before harvesting –

Harvest Harvest soon after maturity (95% mature)

Threshing Thresh immediately after harvest; do not leave in the field for drying

Drying, cleaning Clean and dry to <14% moisture content (low‐cost moisture meter to manage grain moisture)

Storage Store in airtight containers (e.g., painted mud pots, metal drums, super bags)

Millingd Mill at right moisture content (12–14% MC) (rice‐milling chart; portable grain quality test kit)

aTPR, transplanted rice; DSR, direct‐seeded rice.bPI, panicle initiation.cIPM, integrated pest management.dMC, moisture content.

INCREASIN

GRIC

EPRODUCTIO

NIN

SUB‐SAHARAN

AFRIC

A119


infected people with a single dose of an appropriate anthelmintic drug will

control the disease eVectively in all areas, including wetland rice areas

(WARDA, 1999).

B. ENVIRONMENTAL ISSUES RELATED TO RICE INTENSIFICATION IN SSA

Rice intensification in SSA must take preventive measures to protect

the environment and ensure the long‐term sustainability of rice farming.

IRRI has developed five environmental indicators to monitor production,

biodiversity, pollution, land degradation, and water (IRRI, 2004).

� Production: For rice production to be sustainable in the long run, it is

important to preserve the natural resources—land, water, and soil fauna

and flora—that support rice production. Combining balanced fertilizer

use with adequate weed control will enhance rice yields and maintain soil

fertility in rainfed and irrigated wetlands of SSA (WARDA, 1998). Con-

servation agricultural methods such as zero tillage, planted fallows with

legumes, and dryland rice‐cover crop rotations are being developed to

reduce soil erosion, conserve soil moisture, and improve soil fertility in

drylands (Akanvou et al., 2001a; Carsky et al., 2001; Erenstein, 2003;

Somado et al., 2003).

� Biodiversity: Preserving wild rice species and diverse cultivated rice vari-

eties in situ in fields and outside in Gene Banks is critical to guard against

pest outbreaks and to supply desirable genes for future needs. Many of the

hardy O. glaberrima lines and varieties would be extinct had their seeds

not been collected and preserved in Gene Banks, because African farmers

had abandoned them to grow their distant Asian cousins (WARDA, 1999,

2001–2002).

We need careful planning based on scientific research to seek a balance

between the economic return of land conversion and social value of

preserving marshlands. It is argued that the conversion of marshlands to

wetland paddies will reduce biodiversity and release a huge amount of

carbon accumulated under the ground. Thus, only high‐potential man-

grove areas must be identified and developed for rice farming and the

remaining mangrove forests preserved in their natural state to save the

richmangrove biodiversity and protect local communities against cyclones

and tsunami‐induced invasion of coastal lands.

Similarly, there is a danger of the harvesting and irreversible drying of peats

in inland valleys and basins. In addition, acid sulfate soils must be kept

flooded all the time to prevent irreversible drying into a nonusable resource.


� Pollution: Herbicides are eVective in controlling weeds in all systems, but

they have to be applied at the right time and at the right dose to destroy

weeds with minimal impact on the environment. The use of IPM for pest

control and SSNM and the LCC for precision nutrient management in rice

will help reduce pesticide‐ and fertilizer‐related pollution of water sources

(Balasubramanian, 2004; Buresh et al., 2003; Dobermann et al., 2004).

Methane emissions from flooded rice fields are an environmental issue

(IRRI, 2004). An estimated 5–10% of global methane emissions are attrib-

uted to flooded rice systems in Asia (Wassmann et al., 2000). Methane

mitigationmeasures developed during the past 20 years include crop residue

management, the addition of various soil amendments, and midseason

drainage (Wassmann et al., 2000); these measures can be proactively

applied in areas of rice intensification in SSA.

� Land degradation: In irrigated rice areas of the semiarid savanna and Sahel

zones, the danger of soil salinization and alkalization must be addressed

through proper drainage and the application of adequate soil amendments

and nutrients to minimize or prevent these types of land degradation

(Massoud, 1977; WARDA, 1999). Conservation agricultural methods

are needed to prevent soil erosion and soil degradation on drylands.

� Water: Water is the most precious natural resource on Earth, and large

amounts of fresh water are diverted to rice cultivation all over the world.

It is therefore important to optimize water productivity by using water‐saving technologies such as AWD, and water‐eYcient short‐duration and

aerobic rice varieties (Bouman et al., 2005, 2006) and hybrid varieties

(Virmani, 1996). The use of less water does not have to obligate farmers

to use more chemical inputs if we develop suitable row‐seeding and line‐transplanting methods and mechanical weed control options. In rainfed

wetlands, RWH is critical to recharge groundwater, revive small streams

and rivers, stabilize rice yields, and diversify farming and income sources.

C. PREPARING FOR THE IMPACT OF CLIMATE CHANGE

Climate change has become a major concern worldwide. SSA will also

face new burdens due to climate change. In SSA, major symptoms of such

a change include the disruption of normal climate patterns over large areas,

increasing incidences of drought and temperature extremes, heavy flooding

and soil erosion/landslides, and increasing levels of salt stress in both inlands

and coastal areas. For example, in Mali, the rainy season is now too short

for rice and the DS is too hot for potatoes. With time, these problems occur

more frequently and with increasing severity, threatening the livelihoods of


resource‐poor farmers. Therefore, underlying processes and the short‐ andlong‐term directions of such changes need to be well understood to formulate

appropriate adaptive strategies and policies for farming under the impact of

changing climate. Solutions require multidisciplinary and integrated appro-

aches to develop a combination of improved rice germplasmwith tolerance of

prevailing and anticipated stresses and adapted crop management as well as

mitigation and amendment strategies that could help simultaneously protect

farmers, consumers, and the environment.

D. TECHNOLOGY DELIVERY AND DEPLOYMENT ISSUES

The new knowledge and technologies must be evaluated in producers’

fields and promoted widely for real impact on productivity and livelihood

of the poor. The technology deployment part is as important as the supply

side of the research‐innovation system. It is important to train, equip, and

motivate field and extension staV of the public and private sectors, nongov-

ernmental organizations, and civil society as well as farmer leaders, and to

strengthen the research‐extension‐farmer linkage to eVectively move new

research findings and technologies from research stations to producers.

Training of and technical support to farmers on new technologies, field

demonstrations, the organization of farmers’ days at harvest time, and

encouragement of farmer‐to‐farmer communication are eVective technologydeployment tools. With the advent of information and communication tech-

nology (ICT), we can now reach out to farmers scattered far and wide. IRRI

has developed a Rice Knowledge Bank (www.knowledgebank.irri.org/)—a

virtual digital extension and training information tool for the extension of

rice technologies. The scheme for the ICT‐based knowledge delivery system

shown in Fig. 9 will help to eVectively deploy rice technologies to producers

and collect farmers’ feedback. The development of a region‐specific Rice

Knowledge Bank for SSA is important for the eVective deployment of rice

technologies.

The voluntary organization of farmers into groups is essential to eVectivelycoordinate farming operations and allocate community resources (water,

grazing land), shape supportive farm policy (crop insurance, minimum

support price, and so on), develop processing and value addition enter-

prises, and take up direct marketing. In addition, training, extension, and

delivery of knowledge are more eVective with farmer groups than with

individual farmers. Private sector‐mediated and supported farmer groups

will enable the timely delivery of the latest technologies with required inputs

and technical support; guarantee farm credit through commercial banks;

develop processing, storage, and marketing facilities in strategic locations;

assure buyback of produce from farmers at a predetermined price in each

http://www.knowledgebank.irri.org/

Riceknowledgebank

Delivery mode Pilot sites

Feedback/experiences/derivativeproducts

Production

Fact sheetsDiagnosticsTraining

resourcesE-learningDatabasesImage library

RuralCyber units- Internet- CD-based

Village 1

HAM radioSMS phone

Mobile ICTvans

Village 2

Village 3

Village n

guides

Figure 9 An example of the ICT‐based knowledge delivery system.


season; and ensure a good‐quality rice supply to national, regional, and

global markets.

E. POLICY SUPPORT FOR RICE INTENSIFICATION IN SSA

It must be emphasized here that the advent of high‐yielding rice varieties

has triggered subsequent changes in supporting policies, such as investments

in irrigation, initiation of credit programs, and the establishment or

strengthening of national research and extension systems in Asia as the

rates of return to such investments increased significantly (Barker and

Herdt, 1985; Hayami and Kikuchi, 1982; Otsuka and Kalirajan, 2005,

2006). The national governments in the major rice‐producing countries of

SSA must design supportive policies for science‐based intensive rice produc-

tion systems based on estimated rates of return to various investments.

In particular, urgent analysis is needed on the benefits of rehabilitation of

irrigation facilities, initiation of farm credit, creation of rural infrastructure

and marketing facilities, and development of public–private partnerships.

The NARIs in many African countries must be revamped and supported to

do relevant research on the emerging issues of intensification of rice farming.

Similarly, the public and private sectors, NGOs, and community extension

services must be trained, equipped, and enabled to provide focused advice

and technical support to rice farmers, small and large. We believe that if


technological breakthroughs are supported by political will, all these

required changes for a Green Revolution in SSA will take root, as occurred

earlier in Asia.

IX. CONCLUSIONS: CHALLENGES TO ANDOPPORTUNITIES FOR ENHANCING

RICE PRODUCTION IN SSA

The cost of irrigated rice production is high in many SSA countries

(FAO‐CORIFA, 2005), mainly because of the high initial investment in

irrigation infrastructure and the poor operation of many irrigated rice

schemes (FAO‐Aquastat, 2005). In addition, irrigated rice farmers have

not realized the full potential of improved irrigated rice varieties due to

less‐than‐optimum input use and crop management. On the other hand,

rainfed wetland rice production by smallholders is often constrained by

many biotic and abiotic stresses as well as inadequate crop management—

all resulting in low yields, less than 1.5 Mg ha�1. Moreover, postharvest

losses are high and the quality of milled rice is often poor in many countries.

Therefore, the production of locally preferred rice at a competitive price is

the biggest challenge to African farmers.

The most important challenge to developing high‐yielding rice varieties

with acceptable grain quality and resistance to or tolerance of local pests in

rainfed and irrigated wetland ecosystems is being addressed progressively.

Although O. glaberrima Steud (African rice) is native to SSA, Asian rice

(O. sativa L.) introduced during the early sixteenth century by European and

Asian traders is cultivated in many irrigated areas of SSA (Buddenhagen,

1986). Breeders are trying to incorporate tolerance of drought and local

biotic stresses into the introduced high‐yielding‐irrigated rice varieties.

Of course, combining high yield with grain quality is critical to transforming

subsistence agriculture into commercial rice farming.

The second challenge lies in identifying, branding, and promoting high‐quality locally adapted rice varieties in national, regional, and international

markets. Although increasing crop yields is very important, a major problem

faced by all SSA rice producers is to reduce postharvest losses, which

presently account for 15–50% of the market value of production.

We believe that to address these challenges, it is critical to improve the

weak rice R&D capacity in SSA. In Mozambique, for example, only 2–3

national scientists are available to address the problems of 500,000 rice

farmers who grow rice on 200,000 ha of land; in Tanzania, only 23 national

scientists are involved in rice research for 322,000 ha of rice land; and, in

Kenya, only 5 researchers are employed to examine the problems of more


than 100,000 rice farmers. Even these limited human and financial resources

tend to be spent on irrigated rice schemes.

The third challenge, the most critical one, is the absence of a coherent and

comprehensive policy, plan, and program to tackle the many constraints and

deficiencies of the national rice sector in African countries. It must be

emphasized here that the development of high‐yielding rice varieties and

profitable production technologies is a prerequisite to trigger changes in

supporting policies, such as investments in irrigation, initiation of credit

programs, revamping of national rice R&D systems, and development of

rural infrastructure and market systems for local rice.

Great opportunities exist to increase rice production and strengthen both

household and national food security in SSA. First, national governments

are trying to increase local rice production to reduce rice imports. Simulta-

neously, the donor community has doubled its aid to SSA for reducing

poverty and improving food security and nutrition. In such an environment,

the vastly underexploited rice sector oVers a tremendous opportunity to

substantially increase local food production and improve food security and

farmers’ income and livelihood.

Donors such as the Rockefeller Foundation and the USAID through

Borlaug LEAP (Leadership Enhancement in Agriculture Program) Fellow-

ships are willing to support the training of a large number of new African

plant breeders and crop production scientists to help develop the agricultural

sector on the continent. In addition, the NEPAD’s (New Partnership for

African Development) CAADP (Comprehensive African Agricultural

Development Program) initiative and various other multilateral facilities

can help develop the rice sector in SSA.

The WARDA and IRRI have a wide array of international expertise in

modern rice breeding, biotechnology, and production and postproduc-

tion management. These two centers are joining hands to help improve

the rice sector in SSA. This is a great opportunity for African agricultural

R&D institutions to improve their rice science and technology‐development

capability through focused training and joint development, and the

implementation of collaborative rice R&D projects.

ACKNOWLEDGMENTS

Earlier review of this chapter and critical comments and suggestions by

Dr. K. L. Sahrawat of ICRISAT, India are gratefully acknowledged. The

authors thank Dr. Bill Hardy for editorial assistance and improvement of

the chapter.


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