Soil quality effects of accelerated erosion and management systems in three eco-regions of Tanzania

Soil quality effects of accelerated erosion and management

systems in three eco-regions of Tanzania

F.B.S. Kaihuraa, I.K. Kullayab, M. Kilasarac,J.B. Auned, B.R. Singhe, R. Lalf,*

aUkiriguru Agriculture Research Institute, PO Box 1433, Mwanze, TanzaniabAgricultural Research Institute Lyamungu, PO Box 3004, Moshi, Tanzania

cSokoine University of Agriculture, Soil Science Department, PO Box 3008, Morogoro, TanzaniadCentre for International Environment and Development Studies-Noragric, NLH, Aas, Norway

eDepartment of Soil Science, NLH, Aas, NorwayfSchool of Natural Resources, Ohio State University, 2021 Coffey Road, Columbus, OH 43210-1085, USA

Received 27 May 1999; received in revised form 8 July 1999; accepted 15 July 1999

Abstract

Soil erosion can adversely in¯uence soil quality, especially in tropical soils. Thus, a multi-location ®eld experiment was

conducted on eight major agricultural soils with different degrees of erosion, in three eco-regions in Tanzania. The objective

was to assess the impact of topsoil depth (TSD) and management on soil properties. Three eco-regions comprising of humid at

Kilimanjaro, sub-humid at Tanga and sub-humid/semi-arid at Morogoro were selected. There were a total of eight locations

within three eco-regions comprising two at Kilimanjaro (e.g., Kirima Boro and Xeno Helena), two at Tanga (Mlingano 1 and

Mlingano 2) and four at Morogoro (Misu®ni 1, Misu®ni 2, Misu®ni 3, and Mindu). The soil management treatments consisted

of farmyard manure (FYM), N and P fertilizer, tie-ridging and farmers' practice. Plant nutrient content was generally lowest

on severely eroded and the highest on least eroded soil classes. Soil pH decreased with increasing severity of erosion on soils

with higher content of Ca�2 in the sub-surface. In general, there occurred a decline in soil organic carbon (SOC) and P with

the decrease in TSD. The SOC content decreased on severely eroded soil class by 0.16%, 0.39% and 0.13% at Misu®ni 1,

Mlingano 1 and Kirima Boro, respectively, compared to slightly or least eroded soil class. Corresponding decline in available

P at these sites was 41%, 62% and 61%, respectively. Application of FYM signi®cantly increased soil pH at some sites. Soil

content of SOC, N, P, K and Mg were signi®cantly increased by FYM application. Signi®cant effects of N and P fertilizers on

SOC and P were observed at most sites. In comparison with farmer's practice, FYM application increased SOC by 0.55%, N

by 0.03%, P by six-fold and K by two-fold. Nitrogen and phosphorus fertilizers had comparable effects for SOC and P only at

some sites. The results indicate that FYM is a better soil input than N and P fertilizers in improving soil quality. The data show

that SOC, N and P are most adversely affected with accelerated erosion and that FYM fertilizer applications have the potential

to improve fertility of eroded soils. # 1999 Elsevier Science B.V. All rights reserved.

Keywords: Soil degradation; Tropical soils; Maize; Cowpeas; Sub-Saharan Africa; Erosion and productivity

Soil & Tillage Research 53 (1999) 59±70

* Corresponding author. Tel.: �1-614-292-2265; fax: �1-614-292-7432

E-mail address: [email protected] (R. Lal)

0167-1987/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.

PII: S 0 1 6 7 - 1 9 8 7 ( 9 9 ) 0 0 0 7 7 - X

1. Introduction

Soil erosion is a major threat to sustainable use of

soil and water resources (Lal, 1998). The threat is

more serious for the soils of the tropics that are highly

susceptible to erosion and other degradative processes.

Erosion in¯uences several soil properties, e.g., topsoil

depth (TSD), soil organic carbon (SOC) content,

nutrient status, soil texture and structure, available

water holding capacity (AWC) and water transmis-

sion characteristics that regulate soil quality and

determine crop yield. Lal (1988) indicated that low

levels of N, P, K, and low cation exchange capacity

(CEC) are among the most important chemical and

nutritional constraints accentuated by soil erosion. Soil

erosion also decreases the AWC (Nizeyimana and

Olson, 1988) and SOC content (Rhoton and Tyler,

1990) and increases soil bulk density (Frye et al.,

1982).

Experiments conducted on Ultisols in Nigeria

showed that maize (Zea mays L.) yield reductions

were 95%, 95% and 100% with 5, 10 and 20 cm re-

moval of TSD, respectively (Mbagwu et al., 1984). For

the same TSD removals on an Al®sol, yield reductions

were 31%, 74% and 94%, respectively. The corre-

sponding yield reductions on an Al®sol at Ilora in

Nigeria were 73%, 83% and 94%, respectively. In all

cases no fertilizer combination was effective in restor-

ing maize yield when TSD was reduced by 10 or

20 cm (Mbagwu et al., 1984). Experiments relating

effects of natural erosion on crop yield have indicated

that the effects are even more severe than that of

arti®cial topsoil removal. Lal (1981) observed that

over a ®ve-year period, the grain yield of maize and

cowpeas (Vigna unguiculata L. Walp.) decreased at

the rate of 9 and 0.7 kg Mgÿ1 of soil loss, respectively.

In another experiment, Lal (1985) observed that maize

yield was reduced 16 times more due to topsoil loss

from natural erosion compared to mechanical topsoil

removal. In some cases, soil quality degraded by

erosion can be improved by judicious use of inputs

and improved soil management practices. Gajri et al.

(1994) observed that application of farmyard manure

(FYM) improved AWC and root growth in soils with

unstable structure and low SOC content. Conventional

or no-tillage plus mulching improved the soil hydro-

thermal regime, resulting greater root growth, nutrient

uptake and grain yields of maize and wheat (Triticum

aestivum L.) on a Typic Hapludalf in India (Acharya

and Sharma, 1994).

In Tanzania, accelerated erosion has occurred since

the pre-colonial period, but the severity and magnitude

of damage had not been adequately assessed. Most of

the work done so far concentrated on assessment of the

amount of soil loss. Ahn (1977) reported that the

Kondoa and Uluguru mountains in central and eastern

Tanzania, respectively, were severely affected by ero-

sion. Ngatunga et al. (1984) observed that soil loss was

greatest on bare fallow soil compared to plowed,

mulched or natural grass conditions. Soil loss ranged

from 38 to 88 Mg haÿ1 on 10% to 22% slope under

bare fallow conditions as compared to 0.08 to

0.10 Mg haÿ1 under natural grass cover for the same

slopes. Recent studies conducted on eight major agri-

cultural soils in Kilimanjaro, Tanga and Morogoro

ecological regions of Tanzania indicated that decrease

in TSD adversely affected a number of soil properties

including SOC, CEC, pH, total soil N (TSN), available

P, AWC, and water saturation percentage (Kaihura et

al., 1996). It was also observed that maize grain yield

was positively and signi®cantly correlated with TSD,

SOC, TSN, CEC, and AWC. Maize yield declined at

38.5, 55 and 87.7 kg cmÿ1 decrease in TSD in Kili-

manjaro, Tanga and Morogoro eco-regions, respec-

tively.

Despite numerous world wide reports on the mag-

nitude and extent of soil erosion and its adverse effects

on soil quality and crop yields, little research has been

done in sub-Saharan Africa on soil management tech-

niques to restore productivity of eroded soils. There-

fore, this study was conducted to evaluate the potential

of selected soil management practices on improving

soil physical and chemical qualities of eroded soils in

three eco-regions of Tanzania.

2. Materials and methods

2.1. Identification of erosion classes

The experiments were conducted on eight major

agricultural soils with different degrees of erosion in

three ecological regions in Tanzania. Eco-region char-

acteristics, as described by De Pauw (1984), and

antecedent soil properties for each soil type are pre-

sented in Table 1. Recognizing that TSD can be

60 F.B.S. Kaihura et al. / Soil & Tillage Research 53 (1999) 59±70

in¯uenced by genetic factors and severity of past soil

erosion, sites were carefully selected within the same

parent and landscape unit so that variation in TSD was

mainly due to soil erosion. With this assumption, the

severity of erosion (e.g., as determined by the depth of

the A horizon) was assessed in 1992 using morpho-

logical characteristics of the top 50 cm depth and by

determining the boundary between the topsoil and the

sub-soil. Surface stoniness, color, soil consistence,

texture and TSD were used to characterize severity

of erosion. The TSD ranges considered to re¯ect differ-

enterosionclasseswere:severelyeroded(<15 cmTSD);

moderately eroded (16±20 cm TSD); slightly eroded

(21±25 cm TSD); and least eroded (> 25 cm TSD).

Details on ecological zone characteristics and criteria

for establishment of erosion classes are presented in

Kilasara et al. (1995a). Cowpeas and maize growth

and yields were determined on each erosion class for

each soil during short rains (from November through

December) of 1992 for cowpeas and long rains (from

March through July) of 1993 for maize (Kilasara et al.,

1995b).

2.2. Soil management treatments

Soil management treatments were imposed on dif-

ferent TSD classes in 1994. In order to alleviate

erosion-induced constraints of low soil productivity

(soil crusting, soil moisture stress and low soil ferti-

lity) that in¯uence crop yield in three eco-regions, four

soil management treatments imposed included:

1. Farmers' practice (FP) or control treatment

involving shallow tillage in Tanga and Morogoro,

and hand hoeing to 10±15 cm depth and planting

in Kilimanjaro.

2. Tie-ridging (TR) or a ridge-furrow system at 1 m

interval with cross-ties for runoff control and

water conservation.

3. Tie-ridging plus 20 Mg haÿ1 FYM on air dry

bases (TR � FYM).

4. Tie-ridging plus N and P fertilizers at recom-

mended rates, i.e., 100 kg N haÿ1 � 13 kg P haÿ1

at Kirima Boro and Xeno Helena; 50 kg

N � 18 kg P at Mlingano and 80 kg N � 36 kg

P haÿ1 at Morogoro.

The recommended rate of FYM applications for

most soils in Tanzania is 20 Mg haÿ1, which is equiva-

lent to application of 59 kg N and 16 kg P haÿ1 in

Tanga and Morogoro, and 15 kg N and 2.5 kg P haÿ1

in Kilimanjaro. The FYM was applied and mixed with

the soil prior to ridging. Urea and triple superpho-

sphate were used as sources of N and P, respectively, at

all sites. Phosphorus was applied at planting and N

was applied in split applications comprising 1/3 at

planting and 2/3 at knee height stage. Ridges were

made 30 cm high, and with cross-ties of 20 cm height

at 1 m interval using hand hoes. Maize was planted as

test crop with variety `Kilima' for Kilimanjaro and

`TMV-1' for Morogoro and Tanga eco-regions,

respectively. Each erosion class constituted a block

in which treatments were randomly distributed and

replicated three times for Mlingano and Morogoro

sites, while erosion class plots and treatments were

randomly distributed in a 2 ha ®eld at Kilimanjaro.

The TSD classes were not replicated as there were not

enough plots in the same TSD class. Gross plot size

was 4.5 m � 4.5 m and harvested area was 9 m2. Each

Table 1

Eco-regions, soil types and selected topsoil properties for each soil type at the beginning of the experiment in 1992

Eco-region Soil type Location pH SOC N Av-P

Taxonomy FAO(H2O) (g kgÿ1) (g kgÿ1) (mg kgÿ1)

Kilimanjaro (humid) Umbric Hapludalfs Humic Nitisols Kirima Boro 7.0 24 2.1 38.0

Umbric Hapludalfs Humic Nitisols Xeno Helena 6.0 20 1.4 7.6

Tanga (sub-humid) Tropeptic Haplustox Rhodic Ferralsols Mlingano 1 6.6 27 2.2 4.0

Typic Rhodustalfs Haplic Lixisol Mlingano 2 6.5 23 1.9 4.0

Morogoro Lithic Eutrochrepts Eutric Cambisols Misufini 1 6.5 12 1.1 <1.0

(sub-humid/ Typic Eutrochrepts Chromic Cambisols Misufini 2 6.6 11 1.2 1.0

semi-arid) Typic Rhodustalfs Chromic Luvisols Misufini 3 6.3 10 1.2 1.0

Ultic Haplustalfs Haplic Alfisols Mindu 5.8 12 1.1 <1.0

F.B.S. Kaihura et al. / Soil & Tillage Research 53 (1999) 59±70 61

plot comprised six rows with 75 cm between and

30 cm within-row spacing. All plots were prepared

using a hand hoe, and the same procedure was

repeated for the second maize crop in 1995.

2.3. Soil sampling and analysis

Soil core samples were obtained from 0 to 10 cm

depth in triplicate from each treatment to determine

bulk density (�b), and measure soil water retention at

0.01 and 1.5 MPa suctions (Cassel and Nielsen, 1986).

The AWC was calculated as a difference between

water content at 0.01 MPa and 1.5 MPa suctions.

Composite topsoil samples from each treatment were

obtained, air dried, ground, and sieved to pass through

a 2 mm sieve. Samples were analyzed for pH in water

and KCl solution (McLean, 1982), SOC (Nelson and

Sommers, 1982), TSN (Bremner and Mulvany, 1982),

available P (Watanabe and Olsen, 1965), CEC and

exchangeable bases (Thomas, 1982). Soil samples

were obtained after crop harvest.

2.4. Statistical analysis

The results obtained were analyzed according to the

ANOVA procedure using MSTAT package (Nissen et al.,

1994).

3. Results

3.1. Antecedent soil properties

The data on antecedent soil properties are presented

in Table 1. According to soil fertility rating (Landon,

1991), soil pH was medium ranging from 5.8 to 7.0

being highest at Kirima Boro in Kilimanjaro eco-

region and lowest at Mindu in Morogoro eco-region.

Soils of the Kilimanjaro eco-region (e.g., Kirima Boro

and Xeno Helena) are of volcanic origin developed in

a humid climate. Therefore, these soils are character-

ized by higher SOC content than those of the semi-arid

regions. The SOC content, depending on the climate

and the parent material, ranged from a low of about

10 g kgÿ1 in the Morogoro eco-region to 20±25 g

kgÿ1 in the Tanga and Kilimanjaro eco-regions. The

TSN was in the low range of <2 g kgÿ1 at all sites

except for Kirima Boro and Mlingano 1 with 2.1 and

2.2 g kgÿ1, respectively. Available phosphorus (Av-P)

was very low for all sites in Tanga and Morogoro and

high at Kirima Boro site. The data suggest that soil

fertility is high, medium and low for soils in Kili-

manjaro, Tanga and Morogoro eco-regions, respec-

tively. In particular, P levels are low and very limiting

to crop yields for Tanga and Morogoro soils.

3.2. Soil properties as affected by topsoil depth

Antecedent soil properties, prior to imposition of

the soil management treatments, are shown in Table 1.

Soil chemical quality was in the order Morogoro <

Tanga < Kilimanjaro eco-regions. This ecological gra-

dient in soil quality is especially true for Av-P, TSN

and SOC content.

3.2.1. Misufini 1 Ð Morogoro eco-region

Soil pH ranged from 6.6 on severely eroded class to

6.4 on moderately eroded class (Table 2). The Av-P

consistently declined with the increasing severity

of erosion. The severely eroded class was also low

in SOC and K� contents by 1.6 g kgÿ1 and 0.38

cmol kgÿ1, respectively, compared to moderately

eroded class. The TSN was low and remained almost

constant for all erosion classes, and there was no clear

trend with regard to erosion for exchangeable bases

and soil bulk density.

Table 2

Effect of soil depth class on soil properties at Misufini 1 eco-regions

Depth class

(cm)a

pH

(H2O)

SOC

(g Kgÿ1)

N

(g Kgÿ1)

Av-P

(mg kgÿ1)

K�

(cmol/kg)

Ca�2

(cmol kgÿ1)

Mg�2

(cmol kgÿ1)

CEC

(cmol kgÿ1)

�b

(Mg mÿ3)

<15 6.57 9.8 1.6 7.01 0.59 11.65 2.22 21.75 1.37

16±20 6.44 11.4 1.6 8.30 0.97 11.11 1.98 21.47 1.41

21±25 6.49 9.9 1.5 9.91 0.78 10.10 2.42 20.75 1.39

a <15: severely eroded; 16±20: moderately eroded; 21±25: slightly eroded.


3.2.2. Kirima Boro and Xeno Helena Ð Kilimanjaro

eco-region

At Kirima Boro, soil pH was higher in severely and

moderately eroded soils compared to the less eroded

classes (Table 3). The SOC, TSN, Av-P, K� and Ca�2

contents were highest in the least and slightly eroded

classes and their concentrations declined with dec-

reasing TSD. The �b decreased with decreasing sever-

ity of erosion. There was no consistent trend in Mg�2

content with regard to the severity of erosion. A similar

trend was observed at Xeno Helena for most nutrients

tested. Unlike at Kirima Boro, Mg�2 content decreased

with erosion severity, and �b was not affected.

3.2.3. Mlingano 1 and 2 sites Ð Tanga eco-region

Soil pH was not much affected by erosion severity

at Mlingano 1 but was lowest on severely eroded class

at Mlingano 2 (Table 4). Average nutrient content was

higher in least and slightly eroded classes compared to

severely and moderately eroded classes. At Mlingano

2, the severely eroded class contained the lowest

content of all soil nutrients. The severely eroded class

was lower by 3.2 g kgÿ1 in SOC, 0.4 g kgÿ1 in TSN

and 2.42 mg kgÿ1 for Av-P compared to the slightly

eroded class. Exchangeable bases decreased consis-

tently with increasing severity of erosion. The �bwas

the highest in the severely eroded class.

3.3. Soil chemical properties as affected by soil

management

3.3.1. Misufini 1 Ð Morogoro eco-region

The application of FYM signi®cantly increased

Av-P, TSN, K�, and Mg�2 contents at Misu®ni 1

(Table 5). The effects of N and P fertilizer application

were not signi®cant on soil nutrient contents. The �b

also signi®cantly decreased with FYM application

(Table 5).

3.3.2. Kirima Boro and Xeno Helena Ð Kilimanjaro

eco-region

Application of FYM signi®cantly increased pH by

0.34 units while N and P fertilizer application slightly

decreased soil pH (Table 6). Increase in Mg�2 and K�

contents were affected by FYM applications only at

Kirima Boro. At Xeno Helena, a signi®cant increase in

SOC and Av-P was observed with both treatments.

The increase in TSN and Av-P was affected by FYM

application only. There were no signi®cant effects on

�b due to soil management at Xeno Helena. Applica-

tion of P fertilizer was a better source of P for both

sites than was FYM application.

3.3.3. Mlingano 1 and 2 in Tanga eco-region

At Mlingano 2, FYM application signi®cantly

increased pH but applications of N and P fertilizers

slightly reduced pH (Table 7). Both treatments sig-

ni®cantly increased soil contents of Av-P, K� and CEC

at Mlingano 1 compared to the FP. Increase in SOC,

Ca�2 and Mg�2 occurred due to FYM application

only. At Mlingano 2, only Av-P content was signi®-

cantly increased by both FYM and fertilizer treat-

ments. The SOC, TSN, K�, Ca�2 and Mg�2 were

increased by FYM application only at Mlingano 2.

There were no signi®cant effects of any treatments on

CEC of the soil.

3.4. Soil physical properties

Effects of TSD and management for two sites on

soil physical properties are shown in Table 8.

Table 3

Effect of soil depth on soil properties at Kirima Boro and Xeno Helena eco-region sites, where ND is not determined

Site Depth

class (cm)

pH

(H2O)

SOC

(g Kgÿ1)

N

(g Kgÿ1)

Av-P

(mg kgÿ1)

K

(cmol kgÿ1)

Ca�2

(cmol kgÿ1)

Mg�2

(cmol kgÿ1)

�b

(Mg mÿ3)

Kirima Boro <15 6.13 24.0 1.6 29.75 1.71 11.29 0.57 1.18

16±20 6.16 25.1 1.6 32.17 1.96 11.02 0.53 1.21

21±25 5.96 25.3 1.7 41.67 1.56 12.48 0.56 1.24

>25 5.89 24.9 1.8 47.75 1.81 13.05 0.57 1.24

Xeno Helena <15 5.87 21.9 2.0 33.08 ND 6.79 0.54 1.09

16±20 5.96 22.0 2.3 34.08 ND 7.73 0.57 1.08

21±25 5.72 22.0 2.0 37.92 ND 7.34 0.60 1.10


Table 4

Effect of soil depth on soil properties at Mlingano 1 and Mlingano 2 eco-region sites where ND is not determined

Site Depth

class (cm)

pH

(H2O)

SOC

(g kgÿ1)

N

(g kgÿ1)

Av-P

(mg kgÿ1)

K�

(cmol kgÿ1)

Ca�2

(cmol kgÿ1)

Mg�2

(cmol kgÿ1)

CEC

(Mg mÿ3)

�b

(Mg mÿ3)

Mlingano 1 <15 6.05 18.9 1.9 2.42 1.36 7.09 2.56 16.10 ND

16±20 6.05 20.0 2.0 1.99 1.20 6.83 2.56 15.14 ND

21±25 5.99 22.8 2.2 3.37 1.43 8.95 2.85 18.58 ND

>25 5.95 21.5 2.0 3.93 1.30 7.70 3.64 19.32 ND

Mlingano 2 <15 6.30 22.1 1.7 5.63 1.00 7.72 3.93 17.33 1.16

16±20 6.46 24.5 2.1 5.76 1.25 8.86 4.27 18.35 1.10

21±25 6.32 25.3 2.1 8.05 1.30 8.17 4.07 17.75 1.14

64

F.B

.S.

Ka

ihu

raet

al./S

oil

&Tilla

ge

Resea

rch53

(1999)

59±70

3.4.1. Effect of topsoil depth

There were minor effects of TSD on �b and the

moisture retention capacity of the soils of Kirima

Boro. These effects at Misifuni 1 were inconsistent

among TSDs. The middle depth of 15±20 cm showed

slightly higher values of �b and moisture content at

saturation and 1.5 MPa suction.

3.4.2. Effect of management practices

Application of FYM decreased �b for both Misu®ni

and Kirima Boro soils (Table 8). Fertilizer application,

although increased the crop yield, did not show any

effect on �b. The moisture retention at 1.5 MPa was

signi®cantly higher with FYM application as com-

pared to FP. No such effect was observed in moisture

retention at saturation.

3.5. Maize yield

Effects of soil management practices on maize

grain yield for eight sites are shown in Table 9.

Application of FYM and fertilizer increased maize

grain yield by 1732 and 1353 kg haÿ1, respectively,

for all sites. The relative increase in maize grain yield

by the application of FYM in comparison with the

control treatment was most pronounced for the Kili-

manjaro eco-region where the increase in yield was

2830 kg haÿ1 for the Kirima Boro site and

2346 kg haÿ1 for the Xeno Helena site. Because of

the favorable soil moisture regime, nutrient use ef®-

ciency may have been higher for the Kilimanjaro

compared with other eco-regions. Application of

FYM increased yield by 915 to 1851 kg haÿ1 for other

two eco-regions. The higher nutrient use ef®ciency for

Table 5

Effect of soil management on soil chemical properties at Misufini 1 eco-region where NS is non-significant

Treatment pH

(H2O)

SOC

(g kgÿ1)

N

(g kgÿ1)

Av-P

(mg kgÿ1)

K�

(cmol kgÿ1)

Ca�2

(cmol kgÿ1)

Mg�2

(cmol kgÿ1)

CEC

(cmol kgÿ1)

�b

(Mg mÿ3)

FP 6.28 0.94 0.15 2.68 0.46 10.79 2.04 20.62 1.46

TR 6.51 0.94 0.15 4.40 0.48 11.24 2.13 21.23 1.38

TR � FYM 6.63 1.33 0.18 19.84 1.48 10.87 2.53 22.37 1.32

TR � NP 6.59 0.94 0.14 6.70 0.71 10.91 2.13 21.07 1.39

LSD (5%) NS NS 0.001c 4.35c 0.31c NS 0.17b NS 0.06a

a Significant at 5% level of probability.b Significant at 1% level of probability.c Significant at 0.1% level of probability.

Table 6

Effect of soil management on soil properties at Kirima Boro and Xeno Helena where ND is not determined and NA is not applicable

Site Treatment pH

(H2O)

SOC

(g kgÿ1)

N

(g kgÿ1)

Av-P

(mg kgÿ1)

K�

(cmol kgÿ1)

Ca�2

(cmol kgÿ1)

Mg�2

(cmol kgÿ1)

�b

(Mg mÿ3)

Kirima Boro FP 5.93 2.07 0.16 27.83 1.52 11.96 0.53 1.22

TR 6.12 2.24 0.16 30.25 1.53 12.21 0.50 1.21

TR � FYM 6.27 2.99 0.18 44.33 2.41 11.91 0.72 1.18

TR � NP 5.81 2.63 0.18 48.92 1.58 11.77 0.48 1.26

LSD (5%) 0.23b 0.20c 0.03a 5.18c 0.43c NS 0.04c 0.03b

Xeno Helena FP 5.62 1.86 0.20 23.22 ND 6.16 0.38 1.11

TR 5.76 1.97 0.18 31.56 ND 7.42 0.42 1.08

TR � FYM 6.19 2.63 0.26 40.44 ND 8.59 1.00 1.08

TR � NP 5.83 2.31 0.20 44.89 ND 6.99 0.48 1.10

LSD (5%) 0.23c 0.23c 0.05b 4.15c NA NS 0.16c NS



Table 7

Effect of soil management on soil chemical properties at Mlingano 1 and Mlingano 2

Site Treatment pH

(H2O)

SOC

(g kgÿ1)

N

(g kgÿ1)

Av-P

(mg kgÿ1)

K�

(cmol kgÿ1)

Ca�2

(cmol kgÿ1)

Mg�2

(cmol kgÿ1)

CEC �b

(Mg mÿ3)

Mlin-gano 1 FP 5.88 2.01 0.20 1.07 0.96 7.32 2.64 16.67 ND

TR 6.00 2.07 0.20 1.48 1.08 7.62 2.93 16.93 ND

TR � FYM 6.22 2.32 0.22 6.45 1.54 8.09 3.31 17.61 ND

TR � NP 5.95 1.93 0.19 2.71 1.73 7.54 2.73 17.95 ND

LSD (5%) NS 0.03c NS 1.17c 0.31b 0.28b 0.33a 0.75a ND

Mlin-gano 2 FP 6.26 2.27 0.18 0.86 0.93 7.19 3.52 15.91 1.11

TR 6.24 2.40 0.19 2.69 1.09 7.58 3.83 17.13 1.13

TR � FYM 6.74 2.62 0.22 14.80 1.93 10.55 5.18 20.65 1.15

TR � NP 6.19 2.30 0.19 7.56 0.78 7.67 3.82 17.55 1.14

LSD (5%) 0.07c 0.24a 0.03a 4.05c 0.24c 1.40b 0.84a NS NS


66

F.B

.S.

Ka

ihu

raet

al./S

oil

&Tilla

ge

Resea

rch53

(1999)

59±70

the Kilimanjaro eco-regions was also evident by the

higher increase in yield due to application of fertilizer

for this eco-region. In comparison with the control

treatment, increase in yield was 2931 kg haÿ1 for the

Kirima Boro site and 2686 kg haÿ1 for the Xeno

Helena site. Increase in maize grain yield with ferti-

lizer application over the control treatment was 581 to

1187 kg haÿ1 for other eco-regions. Therefore, soils of

the Kilimanjaro eco-region respond more to use of

best management practices than those of other eco-

regions.

4. Discussion

4.1. Effect of topsoil depth on soil properties

Soil pH increased with severity of erosion at Mis-

u®ni 1, Kirima Boro and Mlingano 1 sites. At Misu®ni

1, accelerated erosion was also associated with

increase in exchangeable Ca�2 and Mg�2 contents.

Erosion appears to expose the sub-surface material

containing bases that also increased soil pH at this site.

Increase in soil pH with severity of erosion was also

reported by Cihacek and Swan (1994), where soil

erosion exposed the CaCO3 rich material that

increased soil pH. At the other two sites leaching or

illuviation may have concentrated bases in sub-soil at

Kirima Boro and Mlingano 1 such that erosion

exposed sub-soil bases and increased pH. The

decrease in soil pH at Mlingano 2 on eroded soils

may be due to exposure of acidic sub-soil, and decline

in soil fertility as is evidenced by decreases in other

nutrients on the severely eroded class. A similar

decline in soil pH with erosion was reported by Lal

(1981) on Al®sols in Nigeria. Similarly, Manu et al.

(1996), observed decline in soil pH as erosion exposed

the acidic, Al-rich and P de®cient sub-soil for an

Table 8

Physical properties of soils at selected sites in three eco-regions of Tanzania as affected by TSD and management practices where SE is

standard error

Depth Misufini 1 (Morogoro) Kirima Boro (Kilimanjaro)

�b (Mg mÿ3) Moisture content (%) �b (Mg mÿ3) Moisture content (%)

Saturation 1.5 MPa Saturation 1.5 MPa

<15 1.37 35.6 9.0 1.18 33.8 19.0

15±20 1.41 37.6 9.9 1.21 33.2 18.9

21±25 1.39 35.8 10.2 1.24 33.4 19.0

FP 1.40 36.9 9.4 1.22 32.8 18.6

TR 1.40 36.5 9.4 1.21 33.5 19.0

TR � FYM 1.40 36.9 10.5 1.18 32.5 19.3

TR � NP 1.40 35.0 9.3 1.26 32.9 19.2

SE 0.02a 1.9a 0.2a 0.01 0.46 0.18

a Significant at 5% level of probability.

Table 9

Effect of soil management on maize grain yield (kg haÿ1) for eight locations in Tanzania

Misufini 1 Misufini 2 Misufini 3 Mindu Kirima Boro Xeno Helena Mlingano 1 Mlingano 2

Control 3613 4361 3947 3103 1974 3499 1993 2411

Ridges 3925 4024 4241 3584 2170 2954 1915 2933

Ridges � FYM 5454 5317 5759 4840 4804 5448 3384 3361

Ridges � NP 4736 4942 4605 3766 4905 6185 2993 3598

SE 180 271 130 206 80 170 171 248

LSD (5%) 630 949 455 721 280 595 599


Aridisol in Niger. The observed decline in pH with

erosion at Xeno Helena and Mlingano 2 may be

associated with similar processes. The impact of ero-

sion on soil pH is likely to be in¯uenced by the land

use, and speci®c properties and processes associated

with each soil type.

Soil nutrient content declined with decrease in TSD

with lowest concentrations on severely eroded classes

and highest concentrations on slightly and least eroded

classes at all sites. Consistent decrease was observed

for SOC, TSN, Av-P, and K� contents at all sites, and

decrease in only Ca�2, Mg�2 and CEC for sites in

Tanga. A very sharp and consistent decline was

observed for SOC and Av-P suggesting that these

nutrients are drastically in¯uenced by soil erosion.

Since these soils have inherently low to medium

contents of the major plant nutrients (Table 1), erosion

effects on productivity are very severe. Pimentel et al.

(1995) observed that soil erosion causes loss of basic

plant nutrients such as N, P, K� and Ca�2 and that

water erosion selectively removes the ®ne organic

particles leaving large particles and stones on the

surface. Lal (1988) pointed out that progressive soil

erosion increases the magnitude of soil-related con-

straints to production. The constraints can be physical,

chemical or biological. Among important physical

constraints are reduced TSD and loss of AWC. Soil

chemical constraints and nutritional disorders related

to erosion include low CEC, de®ciency of major plant

nutrients (N, P, K) and trace elements (Zn, S), nutrient

toxicity (Al, Mn) and high soil acidity (Lal,

1981,1998). On the other hand, biological constraints

include low microbial biomass carbon and reduced

activity of soil macrofauna (Lal, 1991). A sharp

decrease in plant nutrients in the severely eroded class

at Mlingano 2 indicates that most nutrients are con-

centrated in the surface soil, which makes quality of

these soils highly sensitive to accelerated erosion. The

�b increased with increasing severity of erosion at

Mlingano 2 and decreased at Misu®ni 1. The increase

in �b with erosion may be due to decrease in aggrega-

tion of soil particles because of decline in SOC content

that also reduces the microbial activities in the eroded

soils. Rhoton and Tyler (1990) reported increase in �b

with erosion and associated this with decrease in TSD

to fragipan and decrease in SOC content. The results

for Misu®ni 1, are contrary to observations made by

Rhoton and Tyler (1990).

4.2. Effect of soil management on soil properties

Application of FYM signi®cantly increased soil pH

at both sites in Kilimanjaro and Mlingano 2 in Tanga

but no effects at other sites. Applications of N and P

fertilizers had no effects on soil pH. The increase in

soil pH following FYM application needs further

investigation. Soil contents of SOC, TSN, Av-P, K�

and Mg�2 at Kirima Boro site were signi®cantly

increased by FYM application. In contrast, application

of FYM decreased �b for the Kirima Boro site.

Applications of N and P fertilizers were only effective

for increasing SOC and Av-P at most sites. Increase

in soil chemical quality with FYM application can

be explained by its potential to release CO2;NH�4 ; NOÿ3 ; POÿ3

4 and undecomposed humic pro-

ducts to the soil through mineralization (Stevenson,

1994). In this process FYM also contributes to CEC,

which increased signi®cantly at some sites. Meelu

(1981) reported that application of 12 Mg haÿ1

FYM produced a residual effect equivalent to 30 kg

of N and 13 kg of P to the succeeding crop. The FYM

applied in this study was equivalent to an average of

37 kg N and 9 kg P across sites. This amount was

much lower compared to an average of 77 kg N haÿ1

and 22 kg P added through inorganic fertilizers. John-

son (1986) attributed some effects of FYM to

improvements in AWC and availability of N in ways

that cannot be mimicked by application of N fertili-

zers. These observations support the ®ndings of this

study that FYM is overall more effective in restoring

productivity than fertilizers. The �b was also signi®-

cantly reduced by FYM application. Decrease in �b

may be due to simple physical effect of mixing organic

matter in the mineral fraction or formation of stable

aggregates, which in turn improve water retention,

permits gas exchange and improve permeability. Simi-

lar effects of FYM on soil quality were reported by

Hussain et al. (1988), Tegene, (1992) and Herrick and

Lal (1995).

5. Conclusions

The data support the following conclusions:

� Severely eroded phases contained the least amount

of plant nutrients, the lowest soil pH, and SOC

content.


� Application of FYM increased soil pH, SOC, and

plant available nutrients, and enhanced soil quality.

� Application of N and P fertilizers also increase

SOC content for some sites.

� Maize grain yield was significantly improved by

application of FYM and fertilizer for all sites.

� Adverse effects of severe erosion on soil quality

and crop yield can be mitigated through application

of FYM and judicious use of chemical fertilizers.

Acknowledgements

The authors thank the Research Council of Norway

for ®nancial support to carry out this research in

Tanzania.

References

Acharya, C.L., Sharma, P.D., 1994. Tillage and mulch effects on

soil physical environment, root growth, nutrient uptake and

yield of maize and wheat on an Alfisol in north-west India. Soil

Tillage Res. 32, 291±302.

Ahn, P.M., 1977. Erosion hazard and farming in East Africa. In:

Greenland, D.J., Lal, R. (Eds.), Soil Conservation and

Management in the Humid Tropics. Wiley, New York, pp.

165±176.

Bremner, J.M., Mulvany, C.S., 1982. Nitrogen-total. In: Page,

A.L., Miller, R.H., Keeney, D.R. (Eds.), Methods of Soil

Analysis, part 2, ASA Monograph. ASA, Madison, WI, 595±

624 pp.

Cassel, D.K., Nielsen, D.R., 1986. Field capacity and available

water capacity. In: Klute (Ed.), Methods of Soil Analysis, part

1, Physical and Mineralogical Methods, Agronomy Mono-

graph, vol. 9. ASA, Madison, WI, pp. 901±926.

Cihacek, L.J., Swan, J.B., 1994. Effects of erosion on soil chemical

properties in the north central region of the United States. J.

Soil Water Conserv. 49(3), 259±265.

De Pauw, E.F., 1984. Soils, physiography and agroecological zones

of Tanzania. Crop monitoring and early warning systems.

Ministry of Agriculture, Dar es Salaam/FAO, Rome, Con-

sultancy Final Report.

Frye, W.W., Ebelhar, S.A., Mudorck, L.W., Blevis, R.L., 1982. Soil

erosion effects on properties and productivity of two Kentucky

soils. Soil Sci. Soc. Am. J. 46, 1051±1055.

Gajri, P.R., Arora, V.K., Chaudhary, M.R., 1994. Maize growth

responses to deep tillage straw mulching and farmyard manure

in coarse textured soils of N.W. India. Soil Use Mgmt. 10, 15±

20.

Herrick, J.E., Lal, R., 1995. Soil physical property changes during

dung decomposition in a tropical pasture. Soil Sci. Soc. Am. J.

59, 908±912.

Hussain, S.K., Mielke, L.N., Skopp, J., 1988. Detachment of soil as

affected by fertility management and crop rotation. Soil Sci.

Soc. Am. J. 52, 1463±1468.

Johnson, A.E., 1986. Soil organic matter, effects on soil and crops.

Soil Use Mgmt. 2(3), 97±105.

Kaihura, F.B.S., Kilasara, M., Kullaya, I., Lal, R., Singh, B.R.,

Aune, J.B., 1996. Topsoil thickness effects on soil properties

and maize (Zea mays) yield in three eco-regions of Tanzania. J.

Sust. Agric. 9, 12±30.

Kilasara, M., Kaihura, F.B.S., Kullaya, I.K., Aune, J.B., Singh,

B.R., Lal, R., 1995a. Establishment of criteria for distinguish-

ing levels of past erosion in Tanzania. Norwegian J. Agric. Sci.

21 (suppl.) 61±70.

Kilasara, M., Kullaya, I.K., Kaihura, F.B.S., Aune, J.B., Singh,

B.R., Lal, R., 1995b. Impact of past soil erosion on land

productivity in selected ecological regions in Tanzania.

Norwegian J. Agric. Sci. 21 (suppl.) 71±79.

Lal, R., 1981. Soil erosion problems on Alfisols in Western

Nigeria. 1. Effects of erosion on experimental plots. Geoderma

25, 215±230.

Lal, R., 1985. Soil erosion and its relation to productivity in

tropical soils. In: Swaify, S.A. et al. (Eds.), Soil Erosion and

Conservation. Soil Conservation Society of America, Ankeny,

IA, USA.

Lal, R., 1988. Monitoring soil erosion's impact on crop

productivity. In: Lal, R. (Ed.), Soil Erosion Research Methods.

Soil and Water Conservation Society, Ankeny, IA, USA, pp.

187±200.

Lal, R., 1991. Soil conservation and biodiversity. In: Hawksworth,

D.L. (Ed.), The Biodiversity of Microorganisms and Inverte-

brates: Its Role in Sustainable Agriculture. CAB International,

Wallingford, UK, pp. 89±104.

Lal, R., 1998. Soil erosion impact on agronomic productivity

and environment quality. Critical Rev. Plant Sci. 17, 319±

464.

Landon, J.R., 1991. Booker tropical soil manual. A handbook for

soil survey and agricultural land evaluation in the tropics and

sub-tropics. Longman, NY, USA.

Manu, A., Pfordresher, A.A., Geiger, C.S., Wilding, L.P., Hossner,

L.R., 1996. Soil parameters related to crop growth variability

in Western Niger, West Africa. Soil Sci. Soc. Am. J. 60, 283±

288.

Mbagwu, J.S.C., Lal, R., Scott, T.W., 1984. Effects of desurfacing

of Alfisols and Ultisols in southern Nigeria. 1. Crop

performance. Soil Sci. Soc. Am. J. 48, 828±833.

McLean, E.O., 1982. Soil pH and lime requirement. In: Page, A.L.,

Miller, R.H., Keeney, D.R. (Eds.), Methods of Soil Analysis,

part 2, Chemical and Microbiological Methods, vol. 9, ASA

Monograph. ASA, Madison, WI, USA, pp. 199±224.

Meelu, O.P., 1981. Integrated use of fertilizers and manures in

cropping sequence. Indian Farming Bulletin. PAU, Ludhiana,

India, pp. 75±79.

Nelson, D.W., Sommers, L.E., 1982. Total carbon, organic carbon,

and organic matter. In: Page, A.L., Miller, R.H., Keeney, D.R.

(Eds.), Methods of Soil Analysis, part 2, Chemical and

Microbiological Methods, ASA Monograph. ASA, Madison,

WI, USA, pp. 539±579.


Ngatunga, E.L.N., Lal, R., Uriyo, A.P., 1984. Effects of surface

management on runoff and soil erosion from some plots at

Mlingano, Tanzania. Geoderma 33, 1±12.

Nissen, O., Hovi, K., Krogdahl, S., 1994. Statistical program ENM,

New Version of MSTAT written in turbopascal. Dept. of Plant

Sci., Agric. Univ. of Norway, As, Norway.

Nizeyimana, E., Olson, K.R., 1988. Chemical, mineralogical,

and physical property differences between moderately and

severely eroded Illinois soils. Soil Sci. Soc. Am. J. 52, 1740±

1748.

Pimentel, D., Harvey, C., Resosudarmo, P., Sinclair, K., Kurz,

D., McNair, M., Crist, S., Shpritz, L., Fitton, L., Saffouri,

R., Blair, R., 1995. Environmental and economic costs of

soil erosion and conservation benefits. Science 267, 1117±

1122.

Rhoton, F.E., Tyler, D.D., 1990. Erosion induced changes in soil

properties of a fragipan soil. Soil Sci. Soc. Am. J. 54, 223±228.

Stevenson, F.J. (Ed.), 1994. Humus Chemistry. Genesis, Composi-

tion, Reactions. Wiley, NY, USA.

Tegene, B., 1992. Erosion: Its effects on properties and productivity

of Eutric Nitosols in Gununo area, southern Ethiopia, and some

techniques of its control. African Studies Series A9, Institute of

Geography, University of Berne, Switzerland, 131 pp.

Thomas, G.W., 1982. Exchangeable cations. In: Page, A.L., Miller,

R.H., Keeney, D.R. (Eds.), Methods of Soil Analysis, part 2,

Chemical and Mineralogical Methods, vol. 9, ASA Monograph.

ASA, Madison,WI, USA, pp. 159±165.

Watanabe, F.S., Olsen, S.R., 1965. Test of an ascorbic acid method

for determining P in water on NaHCO3 extracts from soil. Soil

Sci. Soc. Am. Proc. 29, 677±678.


Soil quality effects of accelerated erosion and management systems in three eco-regions of Tanzania

Documents

Transcript of Soil quality effects of accelerated erosion and management systems in three eco-regions of Tanzania