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Influence of nitrogen fertilization on the performance of early and late maturingmaize varieties under natural infestation with Striga hermonthica (Del.) BenthAlpha Yaya Kamara a; Friday Ekeleme a; Lucky Omoigui a; Abebe Menkir a; David Chikoye a; IbrahimYakamba Dugje b; Tahirou Abdoulaye a; Paul Amaza a

a International Institute of Tropical Agriculture, IITA-Ibadan, Nigeria, c/o Lambourn Ltd, Croydon, UK b

Department of Crop Production, University of Maiduguri, Maiduguri, Nigeria

Online Publication Date: 01 April 2009

To cite this Article Kamara, Alpha Yaya, Ekeleme, Friday, Omoigui, Lucky, Menkir, Abebe, Chikoye, David, Dugje, Ibrahim Yakamba,Abdoulaye, Tahirou and Amaza, Paul(2009)'Influence of nitrogen fertilization on the performance of early and late maturing maizevarieties under natural infestation with Striga hermonthica (Del.) Benth',Archives of Agronomy and Soil Science,55:2,125 — 145

To link to this Article: DOI: 10.1080/03650340802342284

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Influence of nitrogen fertilization on the performance of early and late

maturing maize varieties under natural infestation with Strigahermonthica (Del.) Benth

Alpha Yaya Kamaraa*, Friday Ekelemea, Lucky Omoiguia, Abebe Menkira,David Chikoyea, Ibrahim Yakamba Dugjeb, Tahirou Abdoulayea and Paul Amazaa

aInternational Institute of Tropical Agriculture, IITA-Ibadan, Nigeria, c/o Lambourn Ltd,Croydon, UK; bDepartment of Crop Production, University of Maiduguri, Maiduguri, Nigeria

(Received 23 February 2008; final version received 14 July 2008)

Field studies were conducted in northeast Nigeria to evaluate the response ofearly and late-maturing maize varieties infested with natural populations of Strigato different rates of nitrogen (N) fertilizer. There were significant reductions in thenumber of emerged Striga at 120 kg N ha71 for the early varieties and at 60 and120 kg N ha71 for the late varieties. The number of emerged Striga onlysignificantly differed among the late varieties. Averaged across varieties, grainyield of the early varieties was 144% higher at 60 kg N ha71 and 192% higher at120 kg N ha71 than without added N. For the late varieties the increase in grainyield was 85% higher at 60 kg N ha71 and 144% higher at 120 kg N ha71 thanwithout added N. Among the early varieties, TZE COMP4 C3 had significantlylower grain yield than the other varieties. Among the late varieties, grain yields of8338-1-1 and TZB-SR were significantly lower than in the other varieties. Ourresults show that the application of 60–120 kg N/ha to Striga resistant or tolerantvarieties may reduce damage and increase grain yield. Higher economic rates ofreturn was obtained at N rates of 60–120 kg N/ha than the other rates.

Keywords: maize varieties; Striga emergence; nitrogen fertilization; grain yield

Introduction

Striga hermonthica [Del.] Benth, (hereafter Striga), constitutes one of the most severeconstraints to cereal production in the semi-arid and semi-humid areas of sub-Saharan Africa (Oswald and Ransom 2004). Surveys in the northern Guineasavannah of Nigeria (NGS) showed that Striga has remained a serious problem,attacking millet, sorghum [Sorghum bicolor L. Moench], maize [Zea mays L.] andupland rice (Weber et al. 1995; Kim et al. 1997; Showemimo et al. 2002). In northeastNigeria, over 85% of fields planted to maize and sorghum were infested with Striga(Dugje et al. 2006). Grain yield losses ranged from 10–100% for these crops as aresult of Striga infestation (Parkinson et al. 1986; Lagoke et al. 1991; Oikeh et al.1996). Farmers abandon their cereal fields under severe infestation for Striga-freeland (Lagoke et al. 1991; Khan et al. 2006).

The increasing incidence of Striga has been attributed to poor soil fertility andstructure, intensification of land use through continuous cultivation and an

*Corresponding author. Email: a.kamara@cgiar.org

Archives of Agronomy and Soil Science

Vol. 55, No. 2, April 2009, 125–145

ISSN 0365-0340 print/ISSN 1476-3567 online

� 2009 Taylor & Francis

DOI: 10.1080/03650340802342284

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expansion of cereal production (Vogt et al. 1991; Weber et al. 1995; Rodenburg et al.2005; van Ast et al. 2005). In smallholder farms, crop production practises such as soilfertility management, hand weeding, crop rotation and seed treatment have been usedto control Striga with limited success (Showemimo et al. 2002; Oswald and Ransom2004). Oswald and Ransom (2002) also reported that maize varieties from Striga-freenurseries transplanted under rain-fed conditions provided better season-long controlwith 50–100% improvement in grain yield over maize varieties seeded direct.

Although nitrogen (N) relationships between host and Striga are not wellunderstood (Press 1995; Pageau et al. 2003) some studies have documented the effectof N fertilizer on Striga emergence and population and their resultant effect on cerealgrain yield (Kim et al. 1997; Aflakpui et al. 2002; Showemimo et al. 2002; Oswaldand Ransom 2004; Godwin et al. 2005). For example, Showemimo et al. (2002)reported that a combination of fertilizer between 50 and 100 kg N ha71, and somelevel of Striga tolerance reduced Striga emergence and increased sorghum grainyield. They also noted that the effectiveness of N in suppressing Striga depended onthe responsiveness of sorghum varieties to N levels and the Striga infestation. On theother hand, Kim and Adetimirin (1997) reported that N fertilizer applied to maize at60 and 120 kg ha71 did not affect Striga emergence. In another study, Kim et al.(1997) reported that N fertilizer applied at the rate of 120 and 150 kg reducedemergence significantly. In addition, Robinson and Dowler (1990) reported reducedStriga damage on maize at a higher N rate of 280 kg ha71. Aflakpui et al. (2002),found no major effect of N on the relative growth response of maize to Striga. Asnoted by Kim and Adetimirin (1997) sources of Striga infestation may be responsiblefor the inconsistencies observed in most studies that have been carried out underartificial infestation with either very high or low inoculum pressure (Mumera andBelow 1993). The conditions prevailing under artificial infestation may not berepresentative of what obtained under field conditions. There is therefore a need toassess N effect on Striga infestation and damage under natural field conditions.

The extent to which Striga reduces the growth of its host is highly variable anddepends on factors such as host plant genotype, parasite infestation level, andenvironment (van Ast et al. 2005). Limited studies have shown the importance ofintegrating resistant or tolerant crop varieties with N fertilization in Striga controlon sorghum and maize (Kim and Adetimirin 1997; Showemimo et al. 2002). Theinteraction between N and resistant varieties in reducing infestation under naturalpopulations of Striga has not been extensively studied. The potential for reducingStriga infestation in maize from its present level can be realised by integratingappropriate resistant and tolerant maize varieties with adequate N fertilization. TheInternational Institute of Tropical Agriculture (IITA) has developed improvedStriga resistant (does not allow Striga attachment to the root because of lowproduction of germination stimulants or physical barrier) and tolerant (producedappreciable yield under Striga infestation) early and late varieties of maize. Theobjective of this study was to assess the effect of different N fertilizer rates on earlyand late maize varieties infected with natural populations of Striga.

Materials and methods

The study was conducted in Borno State, northeast Nigeria at the IITA CropResearch site at Wandali (10834.30 N, 11858.60 W, altitude 526 masl) in the NGS andSabon-Gari, (10848.50 N 12827.90 W, altitude 460 masl) in the Sudan savanna (SS)

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Nigeria during the 2005 and 2006 cropping seasons. Selected chemical properties ofthe sites before cropping with maize in both years are presented in Table 1. The twoagro-ecologies are characterized by mono-modal rainfall distribution. Averageprecipitation is 900 mm in the NGS and 700 mm in the SS with a growing period of150 days in the NGS and 120 days in the SS. Prior to the establishment of the trial,the land in both sites were planted to sorghum for five years and was observed in2004 to be heavily infested with Striga.

The land was ploughed and ridged using draught animals. In each location, twoseparate experiments adjacent to each other were set up in each year. The design foreach experiment was a split plot with nitrogen assigned to main plot and maizevarieties to subplot. The trial was replicated three times. Four N levels (0, 30 [low],60 [moderate], and 120 [high] kg N ha71) were assigned to main plot in eachexperiment. In one of the experiments five earl-maturing varieties were used in thesubplots while the other had nine late-maturing varieties in the subplots. Amongthe nine late varieties, seven were selected for Striga resistance or tolerance and theremaining two as the susceptible checks (Table 2). Similarly, among the five earlyvarieties, four varieties were selected for tolerance to Striga while the fifth was thesusceptible check. At each site, the experiments were repeated in 2006 in separate butadjacent to plots used in 2005.

Each variety was planted in four rows of 5 m length spaced 0.75 m apart with0.25 m spacing between plants within each row. Three maize kernels were planted in ahole of 5 cm deep. Two weeks after planting, all plants were thinned to one per hill togive a final plant population of 53,333 plants ha71. All plots received 40 kg ha71 eachof P as single super phosphate and K as muriate of potash immediately after planting.All fertilizer was band-applied on ridges. Nitrogen was applied in two equal splits atone week after planting (WAP) and the other half at 5 WAP. Immediately afterplanting, gramozone (1:1-dimethly-4, 4’-bipyridinium dichloride) was applied at therate of 280 g a.i ha71 to control weeds. Hoe weeding was done at 4 WAP.Subsequently, hand pulling of weeds was done regularly to keep the field clean.

Striga damage symptoms and numbers of emerged plants were recorded in bothtrials. Damage symptoms were visually rated at each trial on the two middle rows at9 WAP for early varieties and at 10 WAP for late varieties using a scale of 1 to 9,where 1 ¼ no visible symptoms and 9 ¼ all leaves completely scorched resulting inpremature death (Kim 1994). Similarly numbers of emerged Striga plants werecounted at 9 WAP for the early varieties and at 10 WAP for the late varieties. Maize

Table 1. Characteristic of soils at Wandali and Sabon-Gari in 2005 and 2006.

Wandali Sabon-Gari

Soil properties{ 2005 2006 2005 2006

pH 1:2.5 (H2O) 6.60 6.21 5.43 6.51Organic C (g kg71) 13.50 2.50 8.30 10.8Total N (g kg71) 0.84 1.26 0.98 1.40Available P (mg kg71) 4.40 2.20 4.00 1.90Exchangeable K (Cmol þ kg71) 0.38 0.30 0.32 0.49Textural class SL CL

{Soil samples were analysed for pH, organic carbon, and total N as described by Van Reeuwijk (1992).Exchangeable K and available P were extracted with Mehlich-3 solution (Mehlich 1984). The K in solutionwas determined on flame photometer and the P on a spectrophotometer.

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grain yield was recorded from plants of the two middle rows, excluding the endplants of each row. Ears harvested from each plot were shelled and the percentagegrain moisture was determined using a Dickey-John moisture tester (Model 14998,Dickey-John Corporation, Auburn, USA). Grain yield adjusted to 12% moisturewas computed from the shelled grain.

All data were subjected to an ANOVA using the PROC Mixed procedure (Littellet al. 1996) of SAS (SAS Institute 2001). Each experiment was analysed separatelyfor each year. Replicate was treated as random effect while location, N levels andmaize varieties were treated as fixed effects. Mean differences were determined with t-test based on the SED at 5% level of probability. Pearson’s correlation coefficientbetween grain yield and the other traits was also computed using PROC CORR ofSAS (SAS Institute 2001).

Economic analysis

Budgeting analysis was used to calculate gross margin on maize fertilization andcalculate marginal rate of return compared to no fertilizer for each treatment andvariety. In estimating the gross margin, estimates of variable cost and gross revenuefrom different maize varieties were collected (5 early; 9 late) in 2005 and 2006. Inboth years, a partial budgeting exercise was undertaken comparing the best of themaize varieties under different levels of N at 0, 30, 60 and 120 kg ha71. Total outputwas valued at market price of US$ 0.38 kg71 of maize in 2005 and US$ 0.33 kg71 in2006. The variable costs consist of the cost of fertilizer at US$ 66.3 ha71, US$132.6 ha71 and US$ 265.2 ha71 at 30, 60 and 120 N rates, respectively. To obtaintotal cost of fertilization, labour cost of US$ 100 ha71 for all treatments for fertilizerapplication (dibbling and covering) is added to fertilizer cost. Labour cost is assumedconstant across application rate due to the application method of dibbling andcovering of the fertilizer. With this method there is fixed number of holes to applyfertilizer to per hectare and time to cover all holes is quite similar for all application

Table 2. Characteristics of early and late maturing maize varieties.

Variety Type Colour Reaction to Striga

Early2000 SYN WEC OPV{ White TolerantACR 94 TZE COMP5-W OPV{ White TolerantACR 94 TZE COMP5-Y OPV{ Yellow TolerantEarly STR SYN F2 OPV{ Yellow TolerantTZE COMP4 C3 OPV{ White Susceptible

Late8338-1-1 Hybrid White Susceptible9022-13 STR Hybrid White TolerantACR 97 TZL COMP1-W OPV{ White ResistantIWDC2 SYN F2 OPV{ White TolerantTZB-SR OPV{ White SusceptibleTZL COMP1 SYN-W OPV{ White ResistantTZL COMP1 SYN-Y OPV{ Yellow TolerantTZL COMP1-W C6 F2 OPV{ White Tolerant

Zea-diplo OPV{ White Tolerant

{OPV, open-pollinated variety.

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rate. The other variable inputs (land preparation, seeds, weeding and harvesting) areall assumed to not vary with the variety and therefore constant across treatments.

The gross margin was estimated as:

GM ¼X

piqi�X

rjxj ð1Þ

where: GM ¼ Gross margin; pi ¼ Unit price of maize output i; qi ¼ quantity of maizeoutput i; rj ¼ unit cost of the variable input j; xj ¼ quantity of the variable input j.

After the gross margins are calculated, marginal rate of return can then beestimated. Marginal rate of return over control indicates the pay-off of eachadditional dollar invested above the cost of the control. For each treatment we areevaluating how much each additional dollar invested is retuning to the farmer. Thegross margin from production activities is the gross value of maize variety output lessall the variable costs incurred on the same maize variety during the production year.

The marginal rate of return compared to the control is calculated as follows:

GMt �GM0ð Þ=CFi ð2Þ

where: GMi ¼ Gross margin for fertilization level t (t ¼ {30 N, 60 N, 120 N});GM0 ¼ Gross margin of control; CFt ¼ Cost of fertilization for treatment t(t ¼ {30 N, 60 N, 120 N}).

The marginal rate of return is a more accurate measure of profitability because itis a proportion and comparison can thus be made across investment level of differentmagnitude (Hayashi et al. 2008). We can therefore know for each treatment howmuch each additional dollar invested by the farmer would have retuned to himrelative to the control treatment. In this economic analysis, profitability decision willbe based upon the marginal rate of return compared to the no fertilizer option (ZeroN) for each variety. The relative profitability tells a more accurate story compared tothe gross margin, which measure absolute profitability. For the relative profitabilitymeasure, an option is worth investing in if the rate is above 1. However in riskyenvironment, it is generally accepted that a rate of at least 2 is necessary for wideadoption of fertilization (CIMMYT 1988).

Results and discussion

Striga emergence and host-plant damage

The number of emerged Striga on both early and late maize varieties was influencedby location in both years for the early- and in 2006 for the late varieties (Table 3).For the early varieties, the number of emerged Striga was significantly higher inSabon-Gari than in Wandali in 2005 but a reverse trend was observed in 2006(Table 4). This may be due to the fact that, in 2005, Striga infestation levels weregenerally lower in plots used to evaluate early maturing varieties in Wandalicompared to Sabon-Gari while in 2006 infestation levels were lower in Sabon-Garithan in Wandali in plots used to evaluate the early-maturing varieties. For the latevarieties, the number of emerged Striga was higher in Wandali than in Sabon-Gari inboth years because Striga infestation levels were higher in plots used to evaluate late-maturing varieties in Wandali. For the early varieties, there were significant N6Linteractions in both years. In 2005, N fertilization significantly reduced the numberof emerged Striga in Sabon-Gari.

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Differences between N rates were not significant in Wandali because of the lowlevel of Striga infestation there. In 2006, differences between N rates were onlysignificant in Wandali because of the low level of infestation in Sabon-Gari. N effectson Striga may be dependent on Striga infestation levels. Under high infestations inSabon-Gari in 2005, and in Wandali in 2006 number of emerged Striga wassignificantly lower at 120 kg N-ha71 than at the other N rates. Differences betweenthe other N rates were not significant. Contrary to the findings of Mumera andBelow (1993), N application did not significantly reduce number of emerged Striga inearly maize at very low levels of Striga infestation. Mumera and Below (1993) foundall N rates reduced Striga infection when Striga infestation was less severe and athigh severity of infestation, Striga infection declined only at 90 kg N ha71 For thelate varieties, there was no significant N6L interactions in both years. A significantreduction in Striga number occurred at 60 kg N ha71 at Wandali in 2006 whereas at120 kg N ha71 a significant reduction in Striga number was observed in bothlocations in 2005 and 2006 (Table 4). At 120 kg N ha71, the number of emergedStriga was reduced by 62% in 2005 and 49% in 2006 on the early varieties comparedwith zero N addition. For the late varieties, there was 13% (2005) and 14% (2006)reduction of Striga infestation at 60 kg N ha71 and 37% (2005) and 48% (2006) at120 kg N ha71 compared with zero N addition. These observations agree withprevious studies that reported a significant N effect on Striga at high doses ofapplication (Robinson and Dowler 1990; Mumera and Below 1993; Kim and

Table 3. Probability of F values of response of number of emerged Striga plants, Strigadamage rating maize total dry matter and grain yield.

Emerged Strigaplants plot71 at

9 WAP{Striga

damage rating{ TDM g plant71CGrain yieldkg ha71

Effect 2005 2006 2005 2006 2005 2006 2005 2006

Early maizeLocation (L) 5.0001 5.0001 0.1702 0.8184 5.0001 5.0001 5.0001 0.0025Nitrogenlevel (N)

0.3749 0.2555 5.0001 0.0048 5.0001 0.0012 5.0001 0.0002

L6N 0.0536 0.0023 0.0774 0.0766 0.0007 0.5090 0.0124 0.0472Variety (V) 0.0970 0.6444 0.0039 0.0357 0.8257 0.2828 5.0001 0.2861L6V 0.0999 0.6883 0.1210 0.1015 0.1118 0.5905 0.0645 0.0490N6V 0.8168 0.2861 0.7968 0.8716 0.2770 0.1276 0.2719 0.8945L6N6V 0.8191 0.6127 0.4907 0.8132 0.0509 0.2067 0.5814 0.5834

Late maizeLocation (L) 5.0001 0.2611 0.0112 0.0061 0.1650 0.0001 5.0001 5.0001Nitrogenlevel (N)

0.2599 0.0077 0.0005 0.0019 5.0001 0.0007 0.0002 0.0003

L6N 0.3060 0.6256 0.0123 0.2314 0.0001 0.0402 0.0139 0.0167Variety (V) 0.0002 5.0001 5.0001 5.0001 5.0001 5.0001 5.0001 5.0001L6V 0.5124 0.5521 0.1337 0.3806 0.0939 0.1555 0.0150 0.0218N6V 0.9657 0.8878 0.7157 0.1033 0.7689 0.4516 0.8302 0.6682L6N6V 0.9979 0.8396 0.7640 0.7893 0.6765 0.2539 0.4802 0.4192

{Emerged Striga plants plot71 recorded at 9 and 10 WAP for the early and late maturing maize varieties;{Striga damage rating recorded at 9 weeks after planting for the early maturing and at 10 weeks for the latematuring maize varieties, where 1 ¼ no visible damage symptoms and 9 ¼ severe damage symptoms due toStriga; CTDM, total dry matter.

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Table

4.

Meannumber

ofem

erged

StrigaandStrigadamageratingonearlyandlate

maturingmaizevarietiesunder

naturalinfestationwithStrigain

Sabon-G

ariandWandali,northeast

Nigeria.

Emerged

Strigaplants

plot7

1at9WAP{

Strigadamagerating{

2005

2006

2005

2006

Treatm

ent

SBG?

WDLP

Mean

SBG

WDL

Mean

SBG

WDL

Mean

SBG

WDL

Mean

Earlymaturing(95days)

N-fertilizer

0153.9

6.1

80.0

21.1

169.0

95.0

6.6

6.1

6.3

5.7

6.1

5.9

30

122.5

5.5

64.0

60.1

118.3

89.2

5.4

5.5

5.4

4.7

5.2

4.9

60

110.3

3.7

57.0

44.0

142.7

93.3

4.9

3.7

4.3

4.5

3.6

4.1

120

56.9

3.4

30.2

30.5

65.5

48.0

3.0

3.4

3.2

3.3

3.1

3.2

Mean

110.9

4.7

38.9

123.9

5.0

4.7

4.6

4.5

SED

Location

12.92**

10.73**

0.23

0.22

SED

Nitrogen

26.98

24.74

0.34**

0.45**

SED

L6N

25.83*

21.47**

0.46*

0.43*

Late

maturing(120days)

N-fertilizer

0141.4

176.5

159.0

69.5

103.2

86.4

6.3

5.1

5.7

6.4

5.9

6.1

30

106.5

231.3

168.9

90.1

102.3

96.2

5.1

4.4

4.8

5.4

5.3

5.3

60

84.2

192.4

138.3

78.3

70.7

74.5

4.6

4.5

4.6

4.8

4.7

4.8

120

27.8

173.1

100.5

38.8

50.3

44.5

3.6

3.9

3.7

4.1

3.4

3.8

Mean

90.0

193.3

69.2

81.6

4.9

4.5

5.2

4.8

SED

Location

21.74**

11.03

0.17**

0.13**

SED

Nitrogen

32.57

15.60**

0.26**

0.33**

SED

L6N

43.48

22.06

0.35*

0.26

{ WAP,weeksafter

planting;{ Strigadamageratingrecorded

at9weeksforearlymaturingand10weeksafter

plantingforthelate

maturingmaizevarieties,where1¼

no

visible

damagesymptomsand9¼

severedamagesymptomsdueto

Striga;?SBG,Sabon-G

ari;PWDL,Wandali;**indicatessignificance

atthe0.05level;*indicates

significance

atthe0.01level.

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Adetimirin 1997; Kim et al. 1997; Showemimo et al. 2002). The mechanismunderlying the reduction of Striga infection at high N levels was not the focus in thisexperiment. However, N application in sufficient quantities is reported to enhanceear development in maize (Lafitte and Edmeades 1994) which may affect parasitismby Striga. Because the maize ear and Striga derive assimilates from the same source(Press et al. 1990), enhancement of ear development by N may suppress Striga(Stewart and Press 1990). The suppression of Striga by N may also depend on theform of N applied. Mumera and Below (1993) reported that only urea reduced Strigainfection under high infestation while all N forms reduced Striga under lowinfestation. They concluded that, because all sources of N decreased Striga infectionto about the same extent, the beneficial effects of N was more related to plant Nstatus than to the available N form. In this study two forms of N were applied; NPK15:15:15 containing half of the N applied at planting while the other half was appliedin form of Urea, 4 weeks after planting maize. The combined effects of these twosources of N may have reduced Striga infection. The reduction was however, onlysignificant at N application of 120 kg N ha71 for early varieties and 60–120 kg Nha71 for late varieties. These high rates may however, not be affordable to poorAfrican farmers who normally use as low as 30 kg N ha71 (Kim et al. 1997). The roleof N in reducing Striga infestation is still conflicting. Contrary to our results and thoseof Mumera and Below (1993), other studies by Smaling et al. (1991) and Kamara et al.(2007) found N fertilization did not reduce Striga infestation in early maize underartificial infestation with high doses of Striga. The conflicting results imply that Nfertilization alone may not be sufficient to control Striga.

There was no significant varietal effect on the number of emerged Striga plantson the early varieties. Varietal effects were however, significant for late varieties inboth years. There was however, no significant N6V interaction for the number ofemerged Striga for all maturity groups. Among the early varieties, ACR 94 TZECOMP5-W in 2005 and 2000 SYN WEC in 2006 had the lowest number of emergedStriga plants. The number of emerged Striga on these two varieties did not however,significantly differ from the other varieties (Table 5). The non-significant differencesin the number of emerged Striga among the early varieties is due to the fact thatduring the early stages of the IITA breeding program, the emphasis was on theselection of early maize varieties for tolerance to Striga that allows the parasite toreproduce (Badu-Apraku and Lum 2007) but allows the maize varieties to produceappreciable yield. Among the late varieties, the susceptible hybrid check, 8338-1-1,the commonly grown open pollinated variety (OPV), TZB-SR, the Striga toleranthybrid, 9022-13 STR and an OPV IWDC2 SYN F2 had significantly higher numberof emerged Striga than the remaining five resistant OPVs in both years. Thiscorroborates the findings of Menkir and Kling (2007) who reported that thesusceptible hybrid 8338-1-1 supported the highest number of emerged Striga in afield trial. The lower number of emerged Striga on the resistant OPVs was mainlybecause they were bred for reduced Striga emergence. Resistant varieties have beenreported to produce little or no amounts of the Striga-germination stimulant Strigol(Ejeta 2007). The hybrid 9022-13 STR was bred for tolerance to Striga, which allowsreproduction and high emergence of the parasite with little reduction in grain yield.

Striga damage on all varieties was significantly reduced by N application in 2005and 2006 in both locations (Table 4). Although L6N interactions were significant forhost damage ratings in both years for early maize and in 2006 for late maize, damagerating scores generally decreased with the increase in N rate in both locations and

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years. The interactions were caused by changes in the magnitude of differencesbetween N levels in each location. The reduction in Striga damage with increasing Nsuggests that N reduced the negative effect of Striga infestation in maize. This findingagrees with Kamara et al. (2007) who reported that Striga damage rating on earlymaize significantly reduced with the application of N at 60 and 120 kg N ha71. Ateach location, differences in Striga damage rating scores among all N rates differedsignificantly for both early and late maize varieties in both years. Striga damagerating scores were significantly lower at 30, 60 and 120 kg N ha71 than at 0 kg Nha71 at both locations in 2005 and 2006 for the early varieties and at both locations in2005 and at Sabon-Gari in 2006 for the late varieties. Our result shows that amoderate amount of N [60 kg N ha71] for both maturity groups reduced hostdamage substantially. Reduction in host damage at both locations was substantial in2005 and 2006. Kim et al. (1997) reported that a higher rate of N (120 kg N ha71)significantly reduced damage on late maturing hybrids in the Nigerian savannas. Thesignificant differences between N rates for host-plant damage scores reveal theimportance of host-plant damage symptoms in differentiating the response of the hostvariety to Striga, corroborating the findings of Kim and Adetimirin (1997).

Interactions between variety and nitrogen and between variety and locationswere not significant suggesting that varieties responded similarly to N applicationand location. Among the early varieties Striga damage on ACR 94 TZE COMP5-W

Table 5. Mean number of emerged Striga, Striga damage rating, total dry matteraccumulation plant71, and grain yield of early and late maturing maize varieties across allN fertilizer treatments under natural infestation with Striga in northeast Nigeria.

Emerged Strigaplants plot71 at 9

WAP{Striga damage

rating{ TDM g plant71C

Variety 2005 2006 2005 2006 2005 2006

Early maturing (95 days)2000 SYN WEC 46.3 72.9 5.4 5.0 105.9 105.2ACR 94 TZE COMP5-W 37.1 74.6 4.0 4.1 102.1 119.0ACR 94 TZE COMP5-Y 46.9 76.4 4.7 4.6 102.2 100.0Early STR SYN F2 86.3 94.2 5.1 4.2 101.2 118.9TZE COMP4 C3 72.5 88.8 5.0 4.9 105.1 110.2SED 20.42 16.97 0.36** 0.34** 4.73 10.36

Late maturing (120 days)8338-1-1 278.4 159.9 7.1 7.7 72.4 97.29022-13 STR 148.1 94.3 4.7 5.0 137.6 135.4ACR 97 TZL COMP1-W 107.2 60.0 4.0 4.2 137.4 148.5IWDC2 SYN F2 159.6 80.5 4.5 4.4 128.2 129.0TZB-SR 201.3 99.5 5.3 5.8 100.2 123.8TZL COMP1 SYN-W 60.9 51.1 3.9 4.4 132.8 139.6TZL COMP1 SYN-Y 82.8 44.0 4.6 5.0 117.1 127.5TZL COMP1-W C6 F2 132.4 39.2 4.1 4.2 133.1 141.4Zea-diplo 104.4 50.2 4.1 4.5 130.8 143.0SED 46.11** 23.40** 0.37** 0.27** 8.72** 8.44**

{Emerged Striga plants plot71 recorded at 9 and 10 WAP for the early and late maturing maize varieties;{Striga damage rating recorded at 9 weeks after planting for the early maturing and at 10 weeks for the latematuring maize varieties, where 1 ¼ no visible damage symptoms and 9 ¼ severe damage symptoms due toStriga; TDM, total dry matter; **indicates significance at the 0.05 level; *indicates significance at the 0.01 level.

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was significantly lower than on the three tolerant varieties and the susceptible checkTZE COMP4 C3 in 2005. In 2006 although Striga damage was less on ACR 94 TZECOMP5-W than on ACR 94 TZE COMP5-Y and Early STR SYN F2, thedifferences in host damage score between them were not significant (Table 5). Thiscorroborates the findings of Badu-Apraku and Lum (2007) and Kamara et al. (2007)who reported that ACR 94 TZE COMP5-W recorded the lowest damage ratings inthe West African savannas under artificial infestation with high dosages of Striga.Differences in Striga damage rating score between the susceptible check and the threeother tolerant varieties (ACR 94 TZE Comp5-Y, Early STR SYN F2, 2000 SYNWEC) were not significant, suggesting that these varieties are not always tolerant toStriga. For the late varieties, Striga damage on the susceptible hybrid check, 8338-1-1, followed by the OPV, TZB-SR was significantly higher than on the toleranthybrid, 9022-13 STR, and the seven resistant OPVs in 2005 and 2006 (Table 5). Ourresults agreed with the findings of Menkir and Kling (2007) who reported that8338-1-1 recorded the highest damage ratings among maize varieties evaluated in theNigerian savanna. They also reported lower damage ratings for the tolerant hybrid9022-13 STR and two OPVs (TZL COMP1-W C6 F2 and ACR 97 TZL COMP1-W). Host-plant damage symptom rating represents a visual assessment of the extentof leaf chlorosis and scorching and reduction in plant height as well as ear and tasselsize of the host plant caused by Striga (Menkir and Kling 2007). The rating isobtained by visually integrating the overall appearance of all the plants in Strigainfested plots (Kim 1994). The reductions in Striga damage ratings in the toleranthybrid and seven resistant late OPVs and in one early variety observed in our studiesmay improve the capacity of these varieties to maintain high rate of photosynthesisunder Striga infestation. Gurney et al. (2002) found that a maize variety thatsustained less damage from S. asiatica maintained higher rates of photosynthesisthan those that sustained greater damage. For both maturity groups, there were noN6V interactions for Striga emergence and damage suggesting that the varietiesresponded similarly to N irrespective of their individual responses to Striga. Thiscorroborates findings of Kamara et al. (2007) who found no N6V interactions forStriga emergence and Striga damage under artificial infestation with Striga.

Maize dry matter and grain yield

Maize dry matter of the early varieties was significantly affected by location in bothyears (Table 6), probably due to differences in prevailing weather conditions betweenthe two locations. Total dry matter plant71 was 1.5 times higher in Wandali than inSabon-Gari for the early varieties. At both locations, the application of N fertilizersignificantly increased dry matter in early and late varieties in both years (Table 6).At both locations, maize dry matter plant71 of both early and late varieties increasedlinearly with an increase in N rates in both years. Interaction effects were however,detected between location and nitrogen application because application of 30 kg N/ha at Wandali gave similar DM as application of 120 kg N/ha in Sabon-Gari whichmay indicate efficient use of N at Wandali than at Sabon-Gari. The increase in drymatter with increasing N rates may be due to a reduction in both the numbers ofemerged Striga and the actual damage done to the host plant, which in this studydecreased as N rates increased. This trend is clearly corroborated by the significantinverse relationships between maize dry matter and Striga damage score and numberof emerged Striga in each maturity group (Table 9) in both years. Similarly, other

134 A.Y. Kamara et al.

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studies have shown that maize dry matter increased with increasing N rate (Kamaraet al. 2005). Mumera and Below (1993) reported that N availability duringreproductive growth altered dry matter partitioning in favour of the ear over thevegetative portion. The alteration resulted in increases in grain yield and harvestindex and a decrease in sink-source partitioning and in the concentration of non-structured carbohydrates in the stalk. Based on these data, they concluded that Nfertility can mediate the impact of Striga infestation on maize by altering assimilatepartitioning in favour of the ear. Among the late varieties, the susceptible hybridcheck 8338-1-1 and TZB-SR, had significantly lower dry matter than the othervarieties at both locations in 2005 and 2006 (Table 6). Striga damage score on bothearly and late varieties was negatively and significantly correlated with total maizedry matter plant71 which suggests that Striga on maize had a significant damagingeffect (Table 9). Gworgwor and Weber (1991) reported significant damage onsorghum when N fertilizer was not applied.

Grain yield of all varieties generally increased with increasing rates of N (Tables 7and 8). Interactions were detected between location and N rates and locations andvarieties. For the early maize, differences between N rates were higher in Wandalithan in Sabon-Gari in both years. For late maize, the magnitude of differencesbetween N rates was higher in Sabon-Gari than in Wandali. Averaged over locationsand varieties grain yield of the early varieties was higher by 142% in 2005 and148% in 2006 at 60 kg N ha71 and higher by 211% in 2005 and 174% in 2006 at

Table 6. Mean total dry matter accumulation plant71 of early and late maturing maizevarieties under natural infestation with Striga in Sabon-Gari and Wandali, northeast Nigeria.

TDM g plant71C

2005 2006

Treatment SBG? WDLP Mean SBG WDL Mean

Early maturing (95 days)

N-fertilizer0 41.2 81.4 61.3 52.3 74.4 63.430 63.9 120.2 92.0 97.4 111.7 104.560 79.8 153.9 116.8 113.1 149.8 131.5120 120.5 165.5 143.0 124.1 162.3 143.2Mean 76.3 130.2 96.7 124.6SED Location 2.99** 6.59**SED Nitrogen 6.56** 12.92**SED L 6 N 5.98** 13.44

Late maturing (120 days)

N-fertilizer0 75.5 85.5 80.5 76.0 109.2 92.630 112.4 111.1 111.7 114.1 126.9 120.560 127.4 134.2 130.8 133.6 149.5 141.5120 180.4 142.0 161.2 171.8 172.5 172.2Mean 123.9 118.2 123.9 139.5SED Location 4.11 3.99**SED Nitrogen 5.81** 9.25**SED L 6 N 8.22** 8.07**

{WAP, weeks after planting; CTDM, total dry matter; ?SBG, Sabon-Gari; PWDL, Wandali; **indicatessignificance at the 0.05 level; *indicates significance at the 0.01 level.

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Table

7.

Meangrain

yield

ofearlymaturingmaizevarietiesatdifferentlevelsofnitrogen

fertilizer

under

naturalinfestationwithStrigain

Sabon-G

ari

andWandali,northeast

Nigeria.

Sabon-G

ari

Wandali

Nitrogen

levels(kgha7

1)

Nitrogen

levels(kgha7

1)

Year

Variety

030

60

120

Mean

030

60

120

Mean

2005

(kgha7

1)

(kgha7

1)

2000SYN

WEC

594.7

1651.1

1973.4

3877.4

2024.2

1924.2

2744.4

4334.1

4888.6

3472.8

ACR

94TZE

COMP5-W

519.1

1473.8

1860.0

3607.1

1865.0

1913.8

3134.4

4492.4

4811.0

3587.9

ACR

94TZE

COMP5-Y

648.9

1207.1

1993.0

3229.3

1769.6

2582.9

3932.6

4254.8

4477.7

3812.0

EarlySTR

SYN

F2

463.0

751.1

1996.8

3337.3

1637.1

2296.7

2959.9

3992.2

4849.3

3524.5

TZE

COPMP4C3

532.0

713.2

1742.4

1970.8

1239.6

908.4

1991.8

3300.8

3420.8

2405.4

Mean

551.5

1159.3

1913.1

3204.4

1925.2

2952.6

4074.9

4489.5

SED

L6N

205.39**

SED

L6V

229.63*

SED

L6N6V

459.27

2006

2000SYN

WEC

1035.1

2690.4

2592.9

2803.8

2280.5

1688.2

2009.8

3617.9

3819.2

2783.8

ACR

94TZE

COMP5-W

1198.3

2311.5

3339.8

3521.3

2592.7

1564.5

2837.2

3739.4

4909.0

3262.5

ACR

94TZE

COMP5-Y

897.9

2607.6

4050.7

2984.6

2635.2

1293.8

2478.8

3559.5

4318.8

2912.7

EarlySTR

SYN

F2

1023.9

1852.0

2544.2

2316.5

1934.2

1213.0

2439.6

3654.6

4403.0

2927.6

TZE

COPMP4C3

2424.9

1159.4

2461.7

2918.8

2241.2

822.5

2442.1

3065.1

4037.8

2591.9

Mean

1316.0

2124.2

2997.9

2909.0

1316.4

2441.5

3527.3

4297.6

SED

L6N

356.41**

SED

L6V

398.48**

SED

L6N6V

796.97

**indicatessignificance

atthe0.05level;*indicatessignificance

atthe0.01level.

136 A.Y. Kamara et al.

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Table8.

Meangrain

yield

oflate

maturingmaizevarietiesatdifferentlevelsofnitrogen

fertilizer

under

naturalinfestationwithStrigain

Sabon-G

ariand

Wandali,northeast

Nigeria.

Sabon-G

ari

Wandali

Nitrogen

levels(kgha7

1)

Nitrogen

levels(kgha7

1)

Year

Variety

030

60

120

Mean

030

60

120

Mean

(kgha7

1)

(kgha7

1)

2005

8338-1-1

97.8

665.7

1926.2

3396.2

1521.5

901.9

1809.9

1328.1

2683.2

1680.7

9022-13STR

1039.5

2188.8

3242.1

3944.5

2603.7

2005.4

3527.6

3987.4

4666.6

3546.7

ACR

97TZL

COMP1-W

1101.4

2350.8

1892.3

4028.4

2343.3

2668.3

3256.5

4224.4

4001.5

3537.7

IWDC2SYN

F2

816.4

1928.4

1800.7

3541.9

2021.9

2523.1

3151.5

4516.2

4540.6

3682.8

TZB-SR

813.0

1289.5

2078.5

2788.0

1742.3

1362.6

2255.7

3159.1

3119.7

2474.3

TZL

COMP1SYN-W

1204.1

1391.5

2868.1

3679.6

2285.8

3636.8

3272.4

4391.7

4693.9

3998.7

TZL

COMP1SYN-Y

1129.9

1754.9

2046.7

3317.7

2062.3

2633.1

3117.1

3559.0

4019.5

3332.2

TZL

COMP-W

C6F2

1685.1

1482.7

1664.5

3961.0

2198.3

2712.1

3680.6

3991.0

3845.5

3557.3

Zea-diplo

1413.6

2408.4

2387.4

3120.2

2332.4

2170.7

4268.7

4225.8

5473.0

4034.6

Mean

1033.4

1717.9

2211.8

3530.9

2290.5

3148.9

3709.2

4115.9

SED

L6N

217.91**

SED

L6V

326.86**

SED

L6N6V

653.72

2006

8338-1-1

538.9

1297.4

1596.2

3171.1

1650.9

753.7

1520.7

1838.6

3771.8

1971.2

9022-13STR

1396.0

2594.2

2653.2

4667.3

2827.7

1605.8

2470.7

3409.4

3809.9

2823.9

ACR

97TZL

COMP1-W

1465.2

2005.4

3650.4

4253.6

2843.6

2108.9

3174.0

4014.1

4651.1

3487.0

IWDC2SYN

F2

1139.0

2050.7

2458.9

4567.7

2554.1

1908.4

1705.4

3813.2

4124.5

2887.9

TZB-SR

828.8

2114.0

1853.1

3105.6

1975.4

1586.4

1742.5

2763.2

3215.9

2327.0

TZL

COMP1SYN-W

1452.7

2313.1

2514.8

3981.7

2565.6

1849.6

2691.8

4098.2

5312.0

3487.9

TZL

COMP1SYN-Y

1984.5

1597.0

3349.3

3702.0

2658.2

2171.2

2790.2

3089.5

4361.5

3103.1

TZL

COMP-W

C6F2

2417.1

2816.7

3826.1

4336.4

3349.1

2040.4

2810.9

3880.4

4247.6

3244.8

Zea-diplo

1754.1

2004.9

2847.0

4826.3

2858.1

1937.3

3157.1

4168.2

4690.4

3488.2

Mean

1441.8

2088.2

2749.9

4068.0

1773.5

2451.5

3452.8

4242.7

SED

L6N

187.32**

SED

L6V

280.98**

SED

L6N6V

561.96

**indicatessignificance

atthe0.05level;*indicatessignificance

atthe0.01level.

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Table9.

Coeffi

cientofcorrelationofmaizegrain

yield,totaldry

matter

plant7

1,Strigaem

ergence

anddamageratingscore

forearlyandlate

maturing

maizevarietiesin

northeast

Nigeria.

Earlymaturing

Late

maturing

2005

2006

2005

2006

Variable

Rp-value

Rp-value

Rp-value

Rp-value

Grain

yield

vs.Totaldry

matter

plant7

10.90

5.0001

0.68

5.0001

0.82

5.0001

0.84

5.0001

Grain

yield

vs.Strigaem

ergence

70.49

5.0001

70.09

0.3271

70.40

5.0001

70.41

5.0001

Grain

yield

vs.Strigadamagerating

70.59

5.0001

70.62

5.0001

70.70

5.0001

70.73

5.0001

Totaldry

matter

plant7

1vs.Strigaem

ergence

70.44

5.0001

0.04

0.6753

70.57

5.0001

70.31

5.0001

Totaldry

matter

plant7

1vs.Strigadamagerating

70.59

5.0001

70.55

5.0001

0.72

5.0001

70.66

5.0001

Strigaem

ergence

vs.Strigadamagerating

0.45

5.0001

0.27

0.0030

0.49

5.0001

0.52

5.0001

138 A.Y. Kamara et al.

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120 kg N ha71 compared to that without added N (Table 7). For the late varieties,the increase in grain yield was higher by 78% in 2005 and 93% in 2006 at 60 kg Nha71 and higher by 130% in 2005 and 158% in 2006 at 120 kg N ha71 compared tothat without added N across locations and varieties (Table 8). Location6varietyinteraction was also significant in both years for both maturity groups. In 2005,2000SYN WEC produced the highest grain yield in Sabon-Gari while ACR 94 TZECOMP5-Y produced the highest grain yield in Wandali. Differences between the twovarieties were, however, not significant in each location. In 2006, ACR 94 TZECOMP5-Y produced the highest grain yield in Sabon-Gari while ACR 94 TZECOMP5-W produced the highest grain yield in Wandali. Yield differences betweenthem were also not significant in both locations. Among the early varieties, thesusceptible check TZE COMP4 C3 had lowest grain yield in both locations and years(Table 7). Badu-Apraku and Lum (2007) also found ACR 94 TZE COMP5-W andACR 94 TZE COMP5-Y and TZE W-Pop61368STR C1 were outstanding in termsof higher grain yield, lower Striga emergence counts, and Striga damage ratings.Kamara et al. (2007) also found ACR 94 TZE COMP5-W and ACR 94 TZECOMP5-Y recorded the highest grain yields under artificial infestation with Striga.Among the late varieties, the hybrid 9022–13 produced the highest grain yield inSabon-Gari while Zea diplo produced the highest yield in Wandali in 2005. In 2006,TZL-COMP1-W-C6F2 produced the highest yield in Sabon-Gari while Zea diploproduced the highest grain yield in Wandali. The yield of these three varieties did nothowever significantly differ from the other Striga-resistant varieties. Grain yields ofthe susceptible hybrid check, 8338-1-1 and the commonly grown variety TZB-SRwere significantly lower than the other varieties. These two varieties supported thehighest numbers of emerged Striga and were more damaged than all other varieties.The seven late maturing varieties that recorded higher yields under Striga infestationalso supported lower number of emerged Striga, suggesting that they are resistant toStriga. The Striga tolerant hybrid check, 9022-13 STR had a grain yield that was notsignificantly different from the seven resistant varieties. This suggests that 9022-13STR is tolerant to Striga as reported by Menkir and Kling (2007). They alsoreported that 8338-1-1 recorded the lowest yield while ACR 97 TZL COMP1-W,TZL COMP1-W C6 F2 and 9022-13 STR recorded the highest yields in their fieldevaluation under artificial infestation. There were no N6V interactions for drymatter production and grain yield for both early and late maturing varieties. Thenon interaction confirms the importance of N for maize development in the presenceor absence of other stresses. This corroborates findings of Akintoye et al. (1999),Kamara et al. (2005), and Oikeh et al. (2007) who found no N6V interactions formaize trials under low nitrogen stress conditions in the Nigerian savannas.

Table 10. Gross margin (US$) and marginal return to fertilizer application for four levels ofNitrogen application on early maturing maize varieties in two location of northeast Nigeria.

Years

Sabon-Gari Wandali

0 N 30 N 60 N 120 N 0 N 30 N 60 N 120 N

2005 207 268 (0.37) 485 (1.20) 836 (1.72) 722 942 (1.32) 1296 (2.47) 1319 (1.63)2006 439 542 (0.62) 767 (1.41) 604 (0.45) 439 648 (1.26) 944 (2.17) 1068 (1.72)Average 323 405 (0.50) 626 (1.30) 720 (1.09) 581 795 (1.29) 1120 (2.32) 1194 (1.68)

Note: The numbers in parenthesis are the marginal rate of return, rates above 1 are considered profitable.

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Table

11.

Gross

margin

andmarginalreturn

tofertilizer

applicationforearlymaturingmaizevarietiesin

twolocationofnortheast

Nigeria.

Years

Sabon-G

ari

Wandali

0N

30N

60N

120N

0N

30N

60N

120N

2005

2000SYN

WEC

223

453(1.38)

507(1.22)

1089(2.37)

722

863(0.85)

1394(2.89)

1469(2.05)

ACR

94TZE

COMP5-W

195

386(1.15)

465(1.16)

987(2.17)

718

1010(1.75)

1453(3.16)

1440(1.98)

ACR

94TZE

COMP5-Y

243

286(0.26)

515(1.17)

846(1.65)

969

1309(2.05)

1364(1.70)

1315(0.95)

EarlySTR

SYN

F2

174

115(7

0.35)

516(1.47)

886(1.95)

862

944(0.50)

1265(1.74)

1454(1.62)

TZE

COPMP4C3

199

101(7

0.59)

421(0.95)

374(0.48)

341

581(1.44)

1006(2.86)

918(1.58)

2006

2000SYN

WEC

345

730(2.32)

632(1.23)

569(0.61)

563

504(7

0.36)

974(1.77)

908(0.95)

ACR

94TZE

COMP5-W

399

604(1.23)

881(2.07)

808(1.12)

522

780(1.55)

1014(2.12)

272(2.05)

ACR

94TZE

COMP5-Y

299

703(2.43)

1118(3.52)

630(0.90)

431

660(1.38)

954(2.25)

1075(1.76)

EarlySTR

SYN

F2

341

451(0.66)

615(1.18)

407(0.18)

405

647(1.46)

986(2.50)

1103(1.91)

TZE

COPMP4C3

808

220(7

3.54)

588(7

0.95)

608(7

0.55)

274

648(2.25)

790(2.22)

981(1.94)

Note:Thenumbersin

parenthesisare

themarginalrate

ofreturn,ratesabove1are

considered

profitable.

140 A.Y. Kamara et al.

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Economic analysis

Profitability results are reported separately for early and late maturing varieties ineach location because of differences in responses to N application. In general, Napplication to the five early maturing maize varieties was profitable over the twoyears. Profitability was however, dependent on N application rate and varieties ineach location for each year. In Sabon-Gari, our results indicate that on average, forthe two years, N application at 60 kg ha71 was most profitable with a rate of returnof 1.30 across the early maturing maize varieties. The dominance of 60 kg N ha71

was clear in the Wandali where higher rainfall allowed better responses in both years(Table 10). Our results suggest that for these early maturing maize varieties,application at 60 kg ha71 is an economic optimal. As expected the economic optimalat 60 kg ha71 is lower than the physical one at 120 kg Nha71 because in calculatingprofitability the cost of achieving a result is taking into account. The final decision inchoosing among these two application level should also consider farmers’ incomes inthis region and what they can afford. This explains why most farmers in this regionare using sub-optimal levels like 30 N which are still profitable but not optimal inWandali for example.

In 2005, the variety 2000 SYN WEC has the highest rate of return at anapplication rate of 120 kg N ha71 in Sabon-Gari (Table 11). In Wandali, however,the best rate of return in 2005 was achieved with the variety ACR 94 TZE COMP5-W at an application rate of 60 kg N ha71. In 2006, the variety ACR 94 TZECOMP5-Y gave the highest rate of return in Sabon-Gari at an application rate of60 kg N ha71. At Wandali, the highest rate of return was obtained with the varietyEarly STR SYN F2 with a 60 kg N ha71 application rate. It is worth noting that thevariety, TZE COPMP4 C3, is clearly not profitable due to low response in SudanSavanna (Sabon-Gari) because it rate of return was below 1 in both year (2005 and2006) at all N application levels in this location (Table 11) probably due to its highsusceptibility to Striga which may have drastically reduced yield.

N application was generally, less profitable on late maturing varieties comparedto early maturing ones over the two years. Profitability of nitrogen fertilizerapplication also varied with the application levels and varieties in both locations andyears. In Sabon-Gari, the application level of 120 kg N ha71 had the best rate ofreturn (average of 1.49) in the two years (Table 12). In Wandali however, the bestrate of return of 1.35 was achieved at the application rate of 60 kg N ha71 in bothyears. Application rate of 30 N kg ha71 was never profitable in all location for bothyears. The results suggest that application at 120 kg N ha71 is the economic optimallevel for the Sabon-Gari and application at 60 kg N ha71 is the economic optimal

Table 12. Gross margin (US $) and marginal return to fertilizer application for four levels ofNitrogen application on Late maturing maize varieties in two location of northeast Nigeria.

Sabon-Gari Wandali

Years 0 N 30 N 60 N 120 N 0 N 30 N 60 N 120 N

2005 391 484 (0.56) 604 (0.92) 971 (1.59) 858 1014 (0.93) 1157 (1.29) 1177 (0.87)2006 482 531 (0.30) 686 (0.88) 994 (1.40) 591 650 (0.36) 917 (1.40) 1048 (1.25)Average 436 507 (0.43) 645 (0.90) 982 (1.49) 1037 832 (0.65) 1037 (1.35) 1113 (1.06)

Note: The numbers in parenthesis are the marginal rate of return, rates above 1 are considered profitable.

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Table

13.

Gross

margin

andmarginalreturn

tofertilizer

applicationforlate

maturingmaizevarietiesin

twolocationofnortheast

Nigeria.

Years

Sabon-G

ari

Wandali

0N

30N

60N

120N

0N

30N

60N

120N

2005

8338-1-1

37

86(0.29)

496(1.97)

920(2.42)

338

512(1.05)

265(7

0.31)

640(0.83)

9022-13STR

393

662(1.61)

994(2.58)

1127(2.01)

752

1156(2.43)

1262(2.19)

1384(1.73)

ACR

97TZL

COMP1-W

417

723(1.84)

483(0.29)

1159(2.03)

1000

1054(0.33)

1351(1.51)

1134(0.37)

IWDC2SYN

F2

309

563(1.53)

449(0.60)

975(1.82)

946

1460(0.42)

1460(2.21)

1336(1.07)

TZB-SR

308

322(0.08)

554(1.06)

690(1.05)

511

951(1.01)

951(1.89)

804(0.80)

TZL

COMP1SYN-W

456

360(7

0.57)

852(1.71)

1027(1.56)

1363

1413(7

1.82)

1413(0.22)

1394(0.08)

TZL

COMP1SYN-Y

427

498(0.42)

542(0.49)

890(1.27)

987

1101(0.09)

1101(0.49)

1141(0.42)

TZL

COMP1-W

C6

638

395(7

1.46)

397(7

1.03)

1133(1.36)

1016

1263(1.18)

1263(1.06)

1076(0.16)

Zea-diplo

535

745(1.26)

671(0.58)

815(0.77)

814

1433(3.73)

1351(2.31)

1686(2.39)

2006

8338-1-1

180

267(0.52)

301(0.52)

694(1.41)

251

340(0.54)

380(0.55)

891(1.75)

9022-13STR

466

700(1.41)

654(0.81)

1194(1.99)

535

657(0.73)

903(1.58)

904(1.01)

ACR

97TZL

COMP1-W

489

504(0.08)

987(2.14)

1056(1.55)

702

891(1.13)

1104(1.73)

1184(1.32)

IWDC2SYN

F2

380

519(0.83)

589(0.90)

1160(2.14)

636

402(7

1.41)

1037(1.73)

1008(1.02)

TZB-SR

277

540(1.58)

386(0.47)

672(1.08)

528

414(7

0.69)

688(0.88)

706(0.49)

TZL

COMP1SYN-W

486

606(0.73)

607(0.53)

965(1.31)

616

730(0.69)

1132(2.22)

1404(2.16)

TZL

COMP1SYN-Y

663

367(7

1.78)

886(0.96)

871(0.57)

723

763(0.24)

796(0.31)

1087(1.00)

TZL

COMP1-W

C6

807

775(7

0.20)

1045(1.02)

1083(0.76)

680

770(0.54)

1060(1.63)

1049(1.01)

Zea-diplo

586

503(7

0.50)

718(0.57)

1247(1.81)

645

885(1.44)

1156(2.19)

1197(1.51)

Note:Thenumbersin

parenthesisare

themarginalrate

ofreturn,ratesabove1are

considered

profitable.

142 A.Y. Kamara et al.

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level at Wandali. This is probably due to the higher moisture availability in theWandali site that allowed a better response to N.

At Sabon-Gari, in 2005, the best profitability rate was obtained with the variety9022-13 STR at an application rate of 60 kg N ha71 (Table 13). Whereas in Wandaliin the same year the variety Zea-diplo gave the best rate of return (3.73) at anapplication rate of 30 kg N ha71. In 2006, the best and similar rates of return wereattained at 60 kg N ha71 for ACR 97 TZL COMP1-W and at 120 kg N ha71 forIWDC2 SYN F2. In Wandali, the variety, TZL COMP1 SYN-W dominated with arate of return of 2.22 at application rate of 60 kg N ha71. Fertilization of theVariety, TZB-SR was not also profitable at all application levels. This variety wasvery susceptible to Striga which caused severe yield loss at all N levels. Results showthat higher economic rates of return was obtained at N rates of 60–120 kg N/ha thanthe other rates. Since these two rates suppressed Striga (120 kg N ha71 for earlyvarieties and 60–120 kg N ha71 for late varieties) and reduced Striga damage in themaize varieties, they can be recommended as components of Striga control optionsin the Nigerian savannas.

Conclusions

Results of our study showed a reduction in Striga infestation and damage with theapplication of N fertilizer on all maize varieties. Striga infestation was however, onlysignificantly reduced only at 120 kg N ha71 in the early variety and 60 and 120 kg Nha71 in late varieties. Among early the varieties, ACR 94 TZE COMP5-W and ACR94 TZE COMP5-Y recorded higher grain yields than TZE COMP4 C3 (control).Although there was no significant interaction between variety and N rates for alltraits measured, the application of 60–120 kg N/ha on Striga resistant or tolerantvarieties may reduce damage and increase grain yield. This implies that farmers arebetter off planting tolerant or resistant varieties when they utilize fertilizer both atsub-optimal and optimal levels of N applications. The Striga tolerant or resistantvarieties should be evaluated under farmer conditions before being disseminatedamong them. Higher economic rates of return were obtained at N rates of 60–120 kgN/ha than the other N rates. Since these two rates suppressed Striga (120 kg N ha71

for early varieties and 60–120 kg N ha71 for late varieties) and reduced Strigadamage in the maize varieties, they may be recommended as components of Strigacontrol options in the Nigerian savannas.

Acknowledgements

We thank the Canadian International Development Agency for funding the project PromotingSustainable Agriculture in Borno State, which financed this study, and Rose Umelo foreditorial assistance.

References

Aflakpui GKS, Gregory PJ, Froud-Williams RJ. 2002. Growth and biomass partitioning ofmaize during vegetative growth in response to Striga hermonthica infection and nitrogensupply. Expl Agric. 38:265–276.

Akintoye HA, Kling JG, Lucas EO. 1999. N-use efficiency of single, double, and syntheticmaize lines grown at four N levels in three ecological zones of West Africa. Field CropsRes. 60:189–199.

Archives of Agronomy and Soil Science 143

Downloaded By: [Kamara, Alpha] At: 13:57 24 March 2009

Badu-Apraku B, Lum AF. 2007. Agronomic performance of Striga resistant early-maturingmaize varieties and inbred lines in the savannas of West and Central Africa. Crop Sci.47:737–750.

CIMMYT (International Maize and Wheat Improvement Center). 1988. From agronomic datato farmer recommendation: An economics training manual. Rev. ed. Mexico City, Mexico.Accessed from the website: http://www.cimmyt.org/english/docs/manual/agronomic/manual/part_one.pdf.

Dugje IY, Kamara AY, Omoigui LO. 2006. Infestation of crop fields by Striga species in thesavanna zones of northeast Nigeria. Agric Ecosyst Environ. 116:251–254.

Ejeta G. 2007. Breeding for Striga resistance in sorghum: exploitation of an intricate host-parasite biology. Crop Sci. 47:216–227.

Godwin KS, Aflakpui GK. Froud-williams RJ. 2005. Carbon (13C) and Nitrogen (15N)translocation in maize-Striga hermonthica association. Expl Agric. 41:321–333.

Gurney AL, Grimaneli D, Kanampiu F, Hoisington D, Scholes JD, Press MC. 2002. Domaize cultivars demonstrate tolerance to the parasitic weed Striga asiatica. Weed Res.42:299–306.

Gworgwor NA, Weber HC. 1991. Effect of N-application on sorghum growth, Strigainfestation and the osmotic pressure of the parasite in relation to the host. J Plant Physol.139:194–198.

Hayashi K, Abdoulaye T, Gerard B, Bationo A. 2008. Evaluation of application timing infertilizer micro-dosing technology on millet production in Niger, West Africa. Nutr CyclAgroecosyst. 80:257–265.

Kamara AY, Menkir A, Ajala SO, Kureh I. 2005. Performance of diverse maize genotypesunder nitrogen deficiency stress in the northern Guinea savanna of Nigeria. Expl Agric.41:199–212.

Kamara AY, Menkir A, Chikoye D, Omoigui LO, Ekeleme F. 2007. Cultivar and nitrogenfertilization effects on Striga infestation and grain yield of early maturing tropical maize.Maydica. 52:415–423.

Khan ZR, Midega CAO, Hassanali A, Pickett JA, Wadhams LJ, Wanjoya A. 2006.Management of Striga, Striga hermonthica, and stemborers in sorghum (Sorghum bicolor),through intercropping with green leaf desmodium, Desmodium intortum. Int J PestManage. 52:297–302.

Kim SK. 1994. Genetics of maize tolerance of Striga hermonthica. Crop Sci. 34:900–907.Kim SK, Adetimirin VO. 1997. Response of tolerant and susceptible maize varieties to timing

and rate of nitrogen under Striga hermonthica infestation. Agron J. 89:38–44.Kim SK, Adetimirin VO, Akintunde AY. 1997. Nitrogen effects on Striga hermonthica

infestation, grain yield, and agronomic traits of tolerant and susceptible maize hybrids.Crop Sci. 37:711–716.

Lafitte HR, Edmeades GO. 1994. Improvement for tolerance to low nitrogen in tropicalmaize: II. Grain yield, biomass production, and N accumulation. Field Crops Res. 39:15–25.

Lagoke STO, Parkinson V, Agunbiade RM. 1991. Parasitic weeds and control methods inAfrica. In: Kim SK, editor. Combating Striga in Africa. Proc. Int. Workshop by IITA,ICRISAT, and IDRC, 22–24 August 1988. Ibadan, Nigeria: IITA. p. 3–14.

Littell RC, Milliken GA, Stroup WW, Wolfinger WW. 1996. SAS system for mixed models.Cary (NC, USA): SAS Inst.

Mehlich A. 1984. Mehlich 3 soil test extractant: a modification of Mehlich 2 extractant.Commun Soil Sci Plant Analysis. 15(12):1409–1416.

Menkir A, Kling JG. 2007. Response to recurrent selection for resistance to Strigahermonthica (Del.) Benth in a tropical maize population. Crop Sci. 47:674–684.

Mumera LM, Below FE. 1993. Crop ecology, production and management. Role of nitrogenin resistance to Striga parasitism of maize. Crop Sci. 33:758–763.

Oikeh S, Chude VO, Kling JG, Horst WJ. 2007. Comparative productivity of nitrogen-useefficient and nitrogen inefficient maize cultivars and traditional grain sorghum in the moistsavannas of West Africa. African J Agric Res. 2:112–118.

Oikeh S, Weber GK, Lagoke STO, Award A. 1996. Estimation of yield losses from Strigahermonthica in farmers’ fields in the northern Guinea savanna of Nigeria. Nigerian J WeedSci. 9:1–6.

144 A.Y. Kamara et al.

Downloaded By: [Kamara, Alpha] At: 13:57 24 March 2009

Oswald A, Ransom JK. 2002. Response of maize varieties to transplanting in Striga-infestedfields. Weed Sci. 50:392–396.

Oswald A, Ransom JK. 2004. Response of maize varieties to Striga-infestation. Crop Protect.23:89–94.

Pageau K, Simier P, Le Bizec B, Robins RJ, Fer A. 2003. Characterization of nitrogenrelationships between Sorghum bicolour and root-hemiparasitic angiosperm Strigahermonthica (Del.) Benth using K15NO3 as isotopic tracer. J Expl Bot. 54:789–799.

Parkinson V, Kim SK, Efron Y, Bello L, Dashiel K. 1986. Potential trap crops for Strigacontrol. In: Proceedings of the FAO/OAU All African Government Consultation onStriga control, Maroua, Cameroon; 20–24 October. p. 136–140.

Press MC, Graves JD, Stewart GR. 1990. Physiology of the interaction of angiospermparasites and their higher plant hosts. Plant Cell Environ. 13:91–104.

Press MC. 1995. Carbon and nitrogen relations. In: Press MC, Graves JD, editors. Parasiticplants. London, UK: Chapman and Hall. p. 103–124.

Robinson EL, Dowler CC. 1990. Cultural and edaphic aspects of Striga control. In: Sand PF,editor. Striga research and control in the United States. Monogr. 5. Champagne (IL):Weed Science Society of America.

Rodenburg J, Bastiaans L, Weltzien E, Hess DE. 2005. How can selection for Striga resistanceand tolerance in sorghum be improved? Field Crops Res 93:34–50.

SAS Institute. 2001. Statistical Analysis Software (SAS) user’s guide. SAS Institute, Inc. Cary,NC, USA.

Showemimo FA, Kimbeng CA, Alabi SO. 2002. Genotype response of sorghum cultivars tonitrogen fertilization in the control of Striga hermonthica. Crop Protect. 21:867–870.

Smaling EMA, Stein A, Sloot PNM. 1991. A statistical analysis of the influence of Strigahermonthica on maize yields in fertilizer trials in South Western Kenya. Plant Soil. 138:1–8.

Stewart GR, Press MC. 1990. The physiology and biochemistry of parasitic angiosperms.Annu Rev Plant Physiol. 41:127–151.

van Ast A, Bastiaans L, Katile S. 2005. Cultural control measures to diminish sorghum yieldloss and parasite success under Striga hermonthica infestation. Crop Protect. 24:1023–1034.

Van Reeuwijk LP. 1992. Procedures for soil analysis. 3rd ed. Wageningen, The Netherlands:International Soil Reference and Information Centre.

Vogt W, Sauerborn J, Honisch M. 1991. Striga hermonthica distribution and infestation inGhana and Togo on grain crops. In: Ransom JK, Musselman LJ, Worsham AD, ParkerC, editors. Proc 5th Int symposium of parasitic weeds by CIMMYT, Nairobi, Kenya. p.372–377.

Weber G, Elemo K, Lagoke STO, Award A, Oikeh S. 1995. Population dynamics anddeterminants of Striga hermonthica on maize and sorghum in savanna farming systems.Crop Protect. 14:283–290.

Archives of Agronomy and Soil Science 145

Downloaded By: [Kamara, Alpha] At: 13:57 24 March 2009