EVALUATION OF MAIZE ( Zea mays. L)- COWPEA( Vigna unguiculata.L) INTERCROPPING SYSTEM FOR IMPROVED WEED MANAGEMENT AND LAND USE.

S.Simunji, D. Mbewe, K. Munyinda, W. Muliokela, D. Moono

ABSTRACT

Weed control in maize fields among small holder farmers

is a major constraint. Farmers spend about 50% of the

time to control weeds mechanically with hand hoe. Better

and more sustainable methods to control weeds in maize

crop need to be developed for small scale farmers who may

not afford to purchase herbicides. Thus maize- cowpea

inter crop farming system is one of the identified

methods that should be tried to provide a solution of

weed problem among smallholder farmers in Zambia.

Therefore a study of using cowpea as intercrop in maize

to control weeds was conducted at Golden valley

Agricultural Research Trust (GART) of Region II of the

three Zambian agro ecological zones.

The trial design was arranged in a Randomized Complete

Block Design with nine treatments replicated four times.

The treatments comprised of three cropping systems; sole

maize, Maize-Cowpea intercrops and Sole cowpea. Each

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having three weeding regimes (weeded once, two times and

three times). The data collected included weed score,

weed number, maize and cowpea yield, Labour to weed, Land

Equivalent ratio (LER) and partial budget (PB). Apart

from land equivalent ratio and partial budget all data

were subjected to analysis of variance (ANOVA) using

genstat. Statistically significant means were separated

using the LSD 0.05 test.

The results from the study revealed that weeding once in

a sole maize crop significantly reduced maize yield by

18% when compared maize – cowpea inter crop with same

weeding regime. Maize yields of sole maize crop improved

by increasing frequency of weeding to two or three times

and these were similar to yields from maize- cowpea

intercrop weeded once, two or three times. Frequency of

weeding did not show any Cowpea yields differences in the

intercrops but by increasing a weeding regime to three

times in a sole cowpea improved the cowpea grain yield

significantly (P<0.05).At 10 weeks after planting the

maize crop high intensity by weed score, number and dry

matter was noticed in the sole maize crop.

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This indicated that cowpea cover crop was able to

suppress weed species such as Cynodon dactylon,

Eleucine indica, Digitaria ternate, Commelina

banghalensis and Cyperus rotundus in the inter crop

and sole cowpea plots. The calculated Land Equivalent

Ratio of 1.91 showed that maize-cowpea intercrop is

significantly beneficial farming system with highest net

benefit coming from weeding once in the maize -cowpea

intercropping farming system It can therefore be

concluded that intercropping maize with cowpea has added

advantage to increase productivity of maize through weed

suppression and increased net benefits.

1.0 INTRODUCTIONWeed control refers to any measure that is used to restrictand reduce weeds in crop- production. Effective weedcontrol, however, depends on various factors that includetype of the crop, timing of operation, nature of the weed,methods of control available to farmers, cost andavailability of human labour (Kambikambi , 2003). Theavailable methods of weed control involve cultural weedmanagement, chemical, biological, preventive and integratedweed management ( Akubondu, 1987). Due to scarcity of

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labour, famers need to make use of the available time andenergy very effectively to control weeds in the fields.Better and more sustainable means have to be introduced inthe farming systems. Some of these methods like biologicalcontrol of weeds with live mulch or intercropping may be ofgreat importance to improve crop productivity in smallholder farms. Although information on the management ofweeds with live mulch is still not complete, results to-date indicate that live mulch in crop production in thetropics can suppress weeds, reduce weed seed population inthe soil, reduce loss in the soil organic matter, providefavourable conditions for earthworm activity, reducesnitrogen requirement of maize, protect soil from erosion,increase moisture infiltration into the soil and reduce soilcompaction. The desirable attributes of suitable live mulchspecies for the tropics should include: low to medium plantheight, aggressiveness, ability to provide complete groundcover rapidly, deep rooting habit, drought tolerance,ability to fix nitrogen, shade tolerance and ease toestablish from seed (Akubondu, 1987). Control of weeds byintercropping ensures that the ground is covered by leafarea more completely and full ground cover occurs early inthe season. Maize intercropped with a fast growing viningcrop such as pumpkin are more efficient in suppressing weedsthan ground nuts and Bambara groundnuts. Maize intercroppedwith cowpeas in Zimbabwe drastically reduced witch weed(Striga asiatica) (Chivinge, 2000). Agricultural practices that involve cultivation of two ormore crops in the same space at the same time is calledintercropping. The practice is often associated withsustainable agriculture and organic farming. It is one formof poly culture using companion planting principles(Ibeawuchi, 2007). In intercropping, there is often one maincrop and one or more added crops, with the main crop beingthe one of the primary importance because of the economic orfood production reasons. The two or more crops used in anintercrop may be from different species and different plant

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families, or they may simply be different varieties orcultivars ( Altieri, 1991). The most common goal ofintercropping is to produce a greater yield on a given pieceof land by making use of the resources that would otherwisenot be utilized by a single crop. Maize (Zea mays L.) is a major food crop in Zambia. One cansafely say that well over 90% of the Zambians consume someform of maize and maize products or indeed products producedwhere maize has been a major input. To confirm this, theZambian Government has over the years through theFertilizer Support Programme (FSP) have spent not less than$ 60 m every season in order to subsidize fertilizer andmaize seed which is made available to a number of smallholder maize farmers . For 2008/2009 farming season thegovernment increased fertilizer subsidy for small scalefarmers from 60% to 75% amounting to 485 billion kwacha(FSP, 2008). To some extent the national agriculturalextension service is also geared towards maize production inpromotion of various sustainable and tested technologies inall parts of the country. Cowpeas which is a food legume andtolerant to drought is of major importance to the live hoodsof millions of relatively poor people in less developedcountries. All plant parts of cowpea crop are used for foodand are nutritious providing protein, vitamins andminerals. The grain contains 23-25% protein and 50-67%starch (Sign et al. 1997). Cowpeas has ability to fix nitrogenthrough symbiotic relation with bacteria thus it does notdeplete natural reserves of nutrients. The above groundparts of cowpeas can also be used as hay to feed the livestock. Oxen maintain health status in dry season enablingtimely land preparation and the return of animal manures tothe land contribute to the soil fertility (Baya et al.2005).With this back ground of maize, cowpeas and intercropping,it can be clear that from the small holder farmer‘s side,that there are some benefits from intercropping system ofmaize and cowpeas. Because of the wide spread use of themaize – cowpea inter cropping system among the farmers in

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country, there is no doubt that this system can have somerobust benefits, apart from the one benefit related tonitrogen fixation as reported by Singh et al; (1997) and hisco workers that cowpeas has capability to contribute to thesoil nitrogen (N) economy at least 40kg N per hectare.Again, intercropping systems might be more advantageous thanmono cropping due to their more efficient of utilizing theavailable resources for economic part of the crop or theirallelopathic effect on weeds (Zahid and Muhamad 2001). Shortage of labour to do timely weeding is a real problem inZambia. There is a gradual loss of effective field labouras a result of the HIV/AIDS Pandemic. Migration ofyoung people from rural to urban areas can not beoveremphasized, but has continued to contribute to thedepletion of effective farm labour on small holder farm(Chivinge 1990; Huang1995). Therefore the problem of weedsis a real one. According to Peter Aaggard verbalcommunication ( 2008), Zambia requires an average of70million man days annually to weed the national cropfields on average of 1,000,000 ha. This shows that smallscale farmer would need 70 man days to weed a hectare offield. This is a significant tying up of human resource toone activity.

Due to weed pressure, maize crop yields have generallybecome low leading into poor food security and poverty. Thenational average yield of maize for 2007/08 season isreported at 1.3 t/ha ( FAO and National Early warning unit,2008). Reminson ( 1978) and Nangju (1980 ) reported thatmaize lose can be as high as 80% if weeds are not controlledwhile Shetto and Kwilinga,1990 stated that uncontrolledweeds can reduce maize yield between 20 to 100% .Kambikakambi ( 2003 an agronomist and lecturer at Universityof Zambia) explained that in Zambia, 25% of crop yield losshas been noted in every field planted due to poor weedcontrol. She adds that 48% of the labour is spent on weedingduring the cropping season which represents a lot of hours

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that could be spend on other activities for development ofthe country. Livestock diseases such as Theileriosis, commonly known ascorridor and caused by Theileria parva parva, have as wellcontributed to the loss of draught animals which could beused for mechanical weed control. Hand hoe weeding thoughslow and high energy demanding appears unfortunately to bethe only mechanism available for many households. This is,however, labour intensive and is back breaking bottom of the weedingtechnology. The other means of weed control would be the useof herbicides which is considered expensive by a majority ofsmall holder farmers (Shetto and Kwiligwa 1990). There fore, introduction of a maize – cowpea intercropping system could possibly provide or contribute asimple biological and more sustainable option means thatsmall scale farmers would easily use to control weeds. Quin(1997) has reported that cowpeas can be used in the intercropping farming system to suppress weeds of which some ofthe varieties cause suicidal germination of the weed seedsof striga hermonthica , a parasitic weed plant which may infestthe cereals, often with devastating effects. On the otherhand the good cover provided by mixed or intercroppingreduces the need for intensive weeding because weeds areheavily shaded and killed under low levels of light ( Ntareand Williams, 1992).

Other than effect of cowpeas on striga weed, other weedspecies that could be controlled by cowpeas in maize –cowpeainter crop have not been much investigated ( Musambai et al2002). The information on the economic benefit of usingcowpeas to save labour of controlling weeds in maize as wellnot yet been known. The research is therefore designed toprovide evidence on the magnitude at which cowpeas cancontribute to the weed control in maize production in termsof specific weed species suppressed. The results should also

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be able to provide a recommendation on the weeding frequencyin maize crop.

2.0 MATERIALS AND METHODS

2.1 Location: The trial was conducted at Golden valley Agricultural Research Trust (GART) located in Chisamba . The site has clay loam soils and receives an annual rain fall between 800 to 1000 mm. The trial was planted in a RandomizedComplete Block Design ( RCBD) with four replications. 2.2 Treatments: The treatments were nine comprised of sole bare maize crop,

Maize-Cowpea intercrop and Sole cowpea allwith three weeding regime as follows:

1. Sole maize crop with one manual hand weeding at four weeks afterplanting maize (Mwd1).

2. Sole maize crop with two manual hand weedings at four weeks andseven weeks after planting ( Mwd2).

3.Sole maize crop with three manual hand weeding at four weeks,seven weeks and ten weeks after planting maize (Mwd).4. Maize-cowpea intercrop weeded once at four weeks after planting

maize (MCwd1).5. Maize-cowpea intercrop weeded two times at four weeks and seven

weeks afterplanting maize (MCwd2).6. Maize-cowpea intercrop weeded three times at four weeks, seven

weeks and tenweeks after planting maize (MCwd3). 7. Sole cowpea crop weeded once four weeks after planting maize

(Cwd1).8. Sole cowpea crop weeded two times at four weeks and seven weeks

after planting maize( Cwd2).

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9.Sole cowpea crop weeded three times at four weeks, seven weeksand ten weeks after planting maize (Cwd3).

2.3 Cultural practices: Maize, MRI 514 variety was the main crop and cowpea, Lutembwe variety was a companion crop. The maize crop was planted in five rows of 5m length at a pacing of 90 cm between rows and 25 cm within rows. Cowpeas , (Vigna unguiculata) Lutembwe variety was intercropped between maize rows by drilling the seed at seed rate of 40 kg/ha and thinned to 3- 4cm ( Muliokela and Kaliangile, 1997) 10 days after planting the main crop (GART Year Book, 2007). D compound fertilizer was applied at 400kg/ha as basal dressing and Urea was at 200kg /ha as top dressing on maize crop. Cowpeas received only 200kg/ha of D compound at planting. Weeding regimes were made at three intervals of four weeks, seven weeks and ten weeks after planting the maize crop. Spraying of cowpeas against pests was done with phosikil chemical at 20 and 50 days growth stages ( Jackai and Adalla, 1997).. 2.4 Data collectionThe data were collected from three centre rows of the solemaize, sole cowpeas and two centre rows of the intercroppedcowpea crop. Observations: Visual weed score was assessed by threeindependent scorers on the scale of 1-5 where 1 was more weedsand 5 less or no weeds. The weed species, weed dry matter andnumber were determined from a quadrant of 50cm x 50cm at tworandomly chosen points three times just before every weeding( Wendy, 2007 and Gomes et al, 2007). Mandays to weed weredetermined by timing labour used to weed the plots. Grainyields of maize and cowpeas at 12.5 % and 14% moisture contentrespectively (Muliokela, 1997) were determined. Finally the

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economic benefit analysis on the varying costs and income fromthe main and companion crops was determined.

2.5 Data analysis. The analysis of variance (ANOVA) for themain crop cowpeas yields, weed score, number of weeds andweed dry matter yield was done with the help of Genstat 5,3.22 soft ware (Lawes, 1995). Land productivity of the twocrops was determined using Land Equivalent Ratio (LER) formulaas explained by (Kurt, 1984).

3.0 RESULTS3.1 Visual weeds score. Four weeks after planting maize, visual assessment of weedsat first weeding stage revealed significantly high weedpressure in the treatments with sole maize crop while intercrop and sole cowpeas scored low levels of weeds. Three weekslater, at second weeding, weed levels visually remained highin sole maize crop with a score of 2. Intercrop and solecowpeas weed score at second weeding showed further reductionin weed infestation from average weed score of 3 to as low as4. There was no significant difference in weed infestationobserved among the plots treated with sole maize crop atsecond weeding. Similar observation was noticed in intercropand sole cowpeas plots. At third weeding growth stage of the crop (10 WAP), solemaize plot weeded once was significantly higher in terms ofweed density than the sole maize crop weeded twice and threetimes. Weeding twice in sole maize crop gave similar weedscore as weeding once in inter cropping or sole cowpea crop.Despite having low weed infestation in inter crop and solecowpeas, the weeds score generally increased with reducedfrequency of weeding (Table 1).

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Table1. weed score (1-5) : 1= moreweeds, 5 less weeds.

Treatments 4WAP

7WAP

10WAP

Average

Sole maize weeded once 1.8bZ 2.2b 1.8c 1.9cSole maize weeded twice 1.8b 1.8bc 4.5ab 2.6bSole maize weeded three times 1.3b 1.0c 4.2b 2.2bcMaize cowpea inter cropweeded once 3.6a 4.2a 4.5ab 4.1aMaize cowpea inter cropweeded twice 3.1a 3.5a 5.0a 3.8aMaize cowpea intercrop weededthree times 2.7a 3.5a 5.0a 3.8a Sole cowpea weeded once 3.0a 3.8a 4.8a 3.8aSole cowpea weeded twice 3.1a 4a 5.0a 4.0aSole cowpea weeded three times 2.8a 4a 5.0a 4.0aLSD 0.85 1.06 0.57 0.54CV% 22.7 23.3 8.9 10.9 WAP = Weeks After Planting Maize.

Z = Means in the same column followed by the same letter arenot significantly different according to Duncans MultipleRange Test at 1% level.

3.2. Number of weeds

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Number of weeds varied according to the farming systems used.Weeds were significantly more in sole maize and cowpeacropping systems than in the intercropped plots first weedingfour weeks after planting maize. At first weeding, the solemaize plot accumulated 65% while sole cowpea had 67% moreweeds than in the intercropped plots which received once andtwice weeding regime. The weed number just before a secondweeding, was found non significant different among the threefarming systems in all weeding regimes used. Weeds however,generally reduced in number by 72% in sole maize plots, 48% inintercrop and 76% in sole cowpea plots between the first andsecond weeding stages. Just before the third weeding (10WAP), number of weedsincreased by 1.9 million in the sole maize plots and 0.5million in the sole cowpea plots weeded once. The maize –cowpea inter crop weeded once maintained same number of weedsas at second weeding. The rest of the plots weeded twice hadreduced number of weeds between second and third weedingstages by 67% in the sole maize, 41% in the intercrop and 56%in the sole cowpea. Among farming systems weeded once, solemaize accumulated high number of weeds as compared to that forintercrop and sole cowpea. There was no difference in thenumber of weeds between sole cowpea and maize – intercropweeded once at third weeding stage (10 WAP) ( Table 2).

Table 2. Weed number in millions per hectare

Treatments 4 WAP 7

WAP

10

WAP

Averag

e

Sole maize weeded once

6.5ab

cd 2.0bz 3.9a 4.1ab

Sole maize weeded twice

8.4ab

c 2.0b 1.0c 3.8ab

Sole maize weeded three times 10.1a 2.8ab 0.6c 4.5a

Maize cowpea inter crop weeded 2.4d 1.8b 1.8bc 2.0b

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onceMaize cowpea inter crop weeded

twice 3.4cd 3.5a 0.9c 2.6ab

Maize cowpea intercrop weeded

three times

6.9ab

cd 1.3b 1.1c 3.1ab

Sole cowpea weeded once 9.2ab 2.0b 2.5b 4.6a

Sole cowpea weeded twice

4.3bc

d 1.9b 0.8c 2.3b

Sole cowpea weeded three times

8.3ab

c 1.3b 0.6c 2.2b

LSD 5.0 1.4 1.3 2.0

CV% 41.6 44.7 48.9 41.6WAP = Weeks After Planting Maize.

Z = Means in the same column followed by the same letter arenot significantly different according to Duncans MultipleRange Test at 1% level.

3.3 Weed speciesThe most common weed species in the trial field were 10 broadleaved, 1 Commelina, 1 Cyperus and 3 grass weed species.However, weed species that existed in largest numbers were,Spilanthes maritiana, Ageratum conyzoides, Trichodesma zeylanicum among thebroad leaved; Cyperus rotundus; Commelina bangelensis and Digitaria milanjianaamong the grasses. Cowpea cover crop in both the sole cowpeaand intercrop reduced weed species of Richard scabra, Trycodesmazeylanicum, Agerantum conyzoides , Cyperus rotundus,Commelina bangelensis,Digitaria ternata and elusine indica when assessed six weeks afterweeding once. This reflected 30% of the broad leaved and 75%of the grass weed species controlled found common in the field(Table 3).

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Table 3. Average number of weed species per 0.5 m2 in plots weeded once

at 4WAP. 1st weeding stage- 4 WAP 2nd weeding stage- 7 WAP

3rd weeding stage - 10 WAP

Common weed species Sole M-C sole Sole M-C sole Sole

M-C sole

Broad leaved maize

intercrop

Cowpea

maize

intercrop

Cowpea maize

intercrop

Cowpea

Nicandra physaloides 0.3 0 0 0 0.3 0 0.5 0 3Leucas martinicensis 39 19 18 3.8 11 4.8 8.8 20 5Celosia trigyna 6.3 0 3.8 1.3 2.3 1.3 0.8 0.8 5.8Oldenlandia herbacea 0 0.3 2 0.3 2.3 2.8 0 0 0Spilanthes mauritiana 37 6.8 119 29 9 31 19 19 43Ageratum conyzoides 190 65 238 29 35 21 78 35 41Bidens pilosa 1.5 0.3 1.3 0 0.3 0.8 0.5 0.3 0.5Trichodesma zeylanicum 13 4 7 10 2.5 10 9.8 0.8 2Richardia scabra 13 3.5 21 1.3 3.5 6.5 7 0 3.8Cyperus                  Cyperus rotundus 12 5.3 9.8 6.3 6.3 8 9.5 3.8 8.3 Commelina                  Commelina benghalensis 5 3.8 4.8 3.8 4 3 6.3 2.5 2.3Grasses                  Cynodon dactylon 0  0 0 5.3 0.5 0 4 1.5 1.3Digitaria milanjiana 4.8 0 0 0 2.5 1 0 0 0Digitaria ternata 0.8 9.8 31 12 8 11 20 3.3 7.5Eleusine indica 0 1.3 2.8 0 5 0 6.3 1.5 0

WAP = Weeks After Planting Maize

3.3. Weed dry matterGenerally, and at the first weeding, weed dry matter (WDM) insole maize crop was found significantly high (315 kg ha-1) ascompared to weed dry matter obtained from inter crop (188 kgha-1 and sole cowpea (234 kg ha-1). By second weeding , a trendon weed dry matter showed a reduction in the weight ofweeds in plots with sole maize and sole cowpea but inter cropindicated some increase in the weed dry matter. A change inweight of weeds from first weeding to second weeding among thetreatments was however, not significant at P<0.05.Weed drymatter in the inter crop was significantly higher P< 0.05 thanthat of sole cowpea at second weeding stage (Table 3.

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At third weeding stage (10 WAP), plots weeded once within thefarming system (sole maize, sole cowpea and intercrop)accumulated significant high weed dry matter compared to plotsthat received two and three weedings (Table 3). The weed drymatter from the sole maize weeded once was significantlyhigher ( P<0.001) than for sole cowpea and intercrop weededonce. No difference in dry matter yield was observed in plotsweeded once between intercrop and sole cowpeas at third timeof weeding. At third weeding, plots that received two weedingshad similar weight of weed dry matter (Table 3).

Table 4. Weed dry matter (Kilogram per hectare).

Treatments 4 WAP 7

WAP 10 WAP

Average

Sole maize weeded once 304abz

241b

c 343a 296a

Sole maize weeded twice 305a

197b

c 51c 184bc

Sole maize weeded three times 335a 450a 63c 282a

Maize cowpea inter crop weeded

once 136d

322a

b 209b 222ab

Maize cowpea inter crop weeded

twice 144cd

291b

c 70c 168bc

Maize cowpea intercrop weeded

three times 284ab

216b

c 74c 191bc

Sole cowpea weeded once 276ab

195b

c 192b 221ab

Sole cowpea weeded twice

185bc

d

166b

c 56c 136c

Sole cowpea weeded three times

241ab

c 134c 41c 138c

LSD 100.3 147.3 84.6 73.0

CV% 28.0 41.2 47.5 24.6WAP = Weeks After Planting Maize.

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Z = Means in the same column followed by the same letter are

not significantly different according to Duncans Multiple

Range Test at 1% level.

3.4. Standard Person days required to weed Labour required to weed once in the sole cowpea wassignificantly lower (P<0.05) than weeding one time in the solemaize crop by 42% or 11.2 person days. Weeding one time inthe intercrop did not show any difference with sole maize andsole cowpea labour. Weeding two times in the sole cowpeas needed less labour thanin the sole maize crop by 39% and in the intercrop by 44%.However, labour required to weed two times in sole maize andinter crop was same. Weeding three times in sole maize hadsignificantly more labour required at P<0.05 than for intercrop by 35% and sole cowpeas by 43%. Labour requirement toweed an area increased with frequency of weeding in all thefarming systems.

Fig 1.Standard person days required to weed a hectare for a farming system type andweeding frequency.

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cdb

a

Means followed by the same letter are not significantlydifferent according to Duncans Multiple Range Test at 1%level.

4.5. Maize, Cowpea grain yields and Land Equivalent Ratio. The sole maize weeded once yielded lowest maize grain(6300kgha-1) as compared to sole maize crop weeded twice andthree times with an average yield of 7261 kgha-1 . The maizeyield of 6300 kgha-1 was again lower than yield obtained in theintercrop at all weeding regimes by 20%. There was nosignificant difference in maize yield shown among the solemaize plots that had more than one weeding and the intercroptreatments. On the other hand, weeding three times in a sole cowpea cropshowed 39% significant advantage in cowpea grain yield overweeding once or two times of the same system and the maize -cowpea intercrop. Partial Land Equivalent Ratio obtained from the ratio ofinter crop maize yield to sole maize yield (La) was 1.09while inter crop cowpea yield to sole cowpea yield (Lb) was0.82. Hence the Land Equivalent Ratio ( LER) calculated fromthe sole maize yield, sole cowpea yield and maize- cowpeaintercrop yields was 1.91 (La + Lb ).

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Table 5. Maize and Cowpea grain yields in the farming systems

weeded differently. Treatments Maize

yield

(kg/ha)

Cowpea

yield

( Kg/ha) Sole maize weeded once 6300bz

Sole maize weeded Two times 7380a

Sole maize weeded Three times 7142a

Maize – Cowpea inter cropping weeded once 7655a 364bz

Maize – Cowpea inter cropping weeded Two times 7353a 418b

Maize – Cowpea inter cropping weeded Three times 7686a 378b

Sole Cowpeas weeded once 420b

Sole Cowpeas weeded once 358b

Sole Cowpeas weeded three times 638a

LSD ( 0.05) 797.3 139.3CV % 8.6 21.5WAP = Weeks After Planting Maize.

Table 6. Land Equivalent Ratio(LER)

  Yield   Farming systems kg ha-1 LERSole maize average yield Sa) 6921  Intercrop average maize yield (Ya) 7565  

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Z = Means in the same column followed by the same letter arenot significantly different according to Duncans Multiple

Intercrop average Cowpea yield (Yb) 387  Sole Cowpea average yield (Sb) 472  

La: Partial LER ( Ya/Sa)   1.09

Lb: Partial LER (Yb/Sb)   0.82

Land Equivalent Ratio (La+Lb)   1.91

3.6 Partial budgeting.Comparison of the sole maize and maize-cowpea intercrop showedhigh net benefit from maize intercrop farming system. Weedingonce in sole maize had lower net benefit than weeding once inthe intercrop by 31%. Therefore, the net benefit for weedingonce in a sole maize crop was the lowest. The benefits in thesole maize crop increased with an increase in the frequency ofweeding, while for intercrop highest benefits were attained atweeding once and three times (Table 5). The total varyingcosts were generally more in the maize- cowpea inter crop thanin sole maize by K1,000,000.

Table7. Partial budgeting.Source of variation

Gross income

 Gross income

Total Gross

Varying costs/ha    

Total cost

Net benefit

 Maize (ZMK)

Cowpea(ZMK)

Income(ZMK) Cowpea

Pesticide

Weeding

Harvesting and

Fertilizer

Varying  

        seed

spraying  

Winnowing labour

for cowpea    

Sole maize weeded once

8,190,000 8,190,000    

212,800   212800

7,977,200

Sole maizeweeded twice 9594000

9,594,000    

290,400     290400

9,303,600

Sole maizeweeded three times 9284000  

9,284,000    

423,200     423200

8,860,800

Maize -cowpea intercrop weeded once. 9951500

1,820,000

11,771,500 200,000 42,000

163,200 304,000

640,000

1,349,200

10,422,300

Maize -cowpea intercrop weeded twice 9558900

2,090,000

11,648,900 200,000 42,000

314,400 304,000

640,000

1,500,400

10,148,500

Maize -cowpea intercrop weeded three times 9991800

1,890,000

11,881,800 200,000 42,000

284,000 304,000

640,000

1,470,000

10,411,800

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4.0 DISCUSSION4.1 Weed intensity Weed intensity that was generally highest in the bare solemaize crop compared to maize- cowpea inter crop and solecowpeas at first and second weeding was evidenced through weedscore, number and dry matter. Many weeds emerged and grew fastfrom the bare soil because they had most advantage to accesssufficient natural resources such as light, moisture andnutrients from the bare soil. Low levels of weed infestationfound in the intercrop and sole cowpea could be explained intwo parts: Firstly, partial weeding could have occurred duringmaking of planting furrows for cowpea 10 days after plantingmaize. Some weeds could have been buried or completely killedwhen making furrows at time of planting cowpea hence theoperation reduced the number of weeds emerged. Secondly,Cowpea which is a broad leafed crop covered the inter rowspacing fast to suppress weeds that were emerging or hademerged but small in size. The results were supported byChivinge (1990) who reported that greater weed growth(biomass) was found in bare ground nuts than in maize-groundnut intercrop. This was attributed to the greater andearlier cover of the ground. Massawe et al.,(2001) also observed areduction of Striga asiatica population over time under the cowpeashading. At third weeding stage (10 WAP), the intensity of weedsassessed through weed number and dry matter were most highestin the treatments that received one weeding in all the threefarming system (Tables 2 and 3). Of the three systems, Solemaize crop weeded once was heavily infested by the weeds ascompared to the weeds in plots of sole cowpea and maize –cowpea intercrop weeded once. This was therefore, enoughevidence to show that soil covering by cowpea in the intercropor sole cowpea has ability to suppress some weeds in thefield. The other aspect to consider is the reduction of weednumber in the field due to increased weeding frequency.Weeding kills seeds of weeds or plants by cutting or leavingthem exposed to the surface where they get desiccated by

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radiation. Weeding may also burry some weeds deeply preventingthe seed to germinate or emerge from the soil. The resultsindicated that leaving weeds in the maize field to continuegrowing after one weeding would result in a high dry matteraccumulation which is correlated to competition against maizecrop. Okobundu (1987) stated that weed density and weight onthe crop is a linear inverse relationship and is sigmoidal. 5.2 Weed species The broad leaved weed species were many in the trial fieldprobably due to high levels of seed production per plant.Chivinge (2003) reported high number of seed production inseveral broad leaved species as compared to grass species.Number of weed species reduced in plots intercropped withcowpeas or in sole cowpea crops by third weeding stage (10WAP). The reduction in the weed numbers observed in 30% ofbroad leaved weed species might be attributed to the shadingand allelopathic effects that could have prevented some weedsto germinate. Michael 2007 supported this effect by reportingthat cover crops could suppress weeds by competing foravailable resources with weeds and by promoting conditionsthat are unfavorable for weed germination and establishment.This is partly due to allelopathy, which is inhibitory orstimulatory of a plant on another species as a result of therelease of chemicals into the environment (Putnam and Tang,1986). Cyperus, Commelina and grassses were most susceptible tocowpea soil covering. Some of the weed species that showedincrease in number over a period of growth in the intercrop orsole cowpea have, however, caused less harm to the main cropas shown by low dry matter weight of weeds. 5.3 Maize and cowpea yields. Maize yield obtained from the bare sole maize crop was lowbecause of weed competition for crop growth factors (water,nutrients and light) against the maize productivity. This wasindicated by high number of weeds and weed dry matteraccumulation for this treatment. According to Okobundu(1987), weeds that are more efficient in water use will have acompetition advantage over less efficient crops like maize.

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Thus presence of the large number of weeds in the maize crophas a negative effect on the growth of maize due to probablypartitioning of a large proportion of soil water resource toweeds. Low maize yield obtained from sole crop with one weeding couldhave also been attributed to competition for light by theweeds and crop. Plants with horizontal and thicker leave tendto intercept more light per unit area and lead to competitivesuperiority if other factors remain constant. In the bare andweeded once plot, weeds were allowed to grow and accumulatehigh biomass that led to low light portioning towards themaize crop. The yield advantage shown by maize and cowpea frommaize – cowpea inter crop system could benefit small holderfarmers through generating sustainable income, minimizing riskof crop failure and providing a source of protein. The maize grain yield which was same between weeding two orthree times in the sole maize crop and one weeding in theintercrop showed how effective cowpea cover crop is inminimizing weed competition on maize crop to enhance increasedcrop productivity. Therefore maize yield in the bare maizecrop could only be increased by weeding more than one time.However, by weeding once in maize –cowpea intercrop, maizeyield was not reduced. This is because cowpeas crop grew fastand had ability to biologically control weeds to a level whereweeds could not cause any significant yield loss. The twocrops (maize and cowpea) hence effectively utilized most ofthe plant resources that would have been exploited by theaggressive weeds.

Cowpea yield from a sole crop weeded three times was higherthan yield from the intercrop with one weeding. It showed thatweeding frequency in sole cowpea crop had an influence in theperformance of cowpeas yield and implied that high yield couldbe achieved in a sole crop by weeding more than two times asthe crop seemed to be sensitive to weeds. The cowpea yieldwhich was similar across the three weeding regimes in the

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intercrop indicated that weeding more than two times in theintercrop was therefore not necessary. This may be becauseweeds accumulated after first and second weeding in theintercrop had less competitive effect against cowpea yield.

5.4 Land Equivalent Ratio The Land Equivalent ratio of 1.91 from this study revealedthat inter cropping was beneficial. The sole maize crop wouldneed 91% more land to produce as same yield as that in themaize – cowpea intercrop. The high LER may be as a result ofincreased yields of maize and cowpea in the intercrop. Thefinding was consistent with Antony et al, (2008) who have reportedthat the LER greater than one often observed with intercropshave been attributed to suppression of weeds, pests andpathogens and enhanced use of resources. According to Francis( 1989) generally when inter specific competition for alimiting resource is less than intra specific competition,there is potential for increased LERs. The component crops(maize and cowpea) in the inter crop system differed in theirpatterns of resource use, which would have resulted in moreefficient resource exploitation when grown together than whengrown in monoculture.

5.5 Labour for weedingWeeding once in all the farming systems indicated lower labourrequirement. However the lowest cost of labour was attainedfrom weeding once in the sole cowpea followed by theintercrop. The intensity of weeds in a sole cowpea at firstweeding was as low as in the intercrop but it was easier toweed a sole cowpea than an intercrop. On the other hand, laborwas highest in the sole maize crop at first weeding due highintensity and biomass of weeds that prevented easy cut ofweeds by a hoe.The cost of weeding increased with frequency of removing weedsfrom the field in the sole maize and cowpea crops. Thehighest labour cost of 56 Standard Person Days to weed ahectare of sole maize crop was attained by weeding three

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times. This result was in agreement with GART year Book,(2003) which stated that it takes 70 Standard Person Days(SPD) to effectively weed the sole maize crop four times.Second weeding of intercrop was costly probably the two cropsthat occupied the same space interfered a smooth cutting andremoval of weeds from the field. However, weeding three timesin the inter crop was not labour costly above weeding twotimes, perhaps the soil cover provided by cowpeas was moreeffective to suppress the weeds. Labour could only be used tohand pull the weeds seen above the cowpea canopy in fewplaces. By weeding once in the intercrop system, farmers havepotential to significantly save 16 SPD and 33 SPD over weedingtwo or three times in the sole maize crop respectively.Labour saving by weeding once in the inter crop is essentiallyimportant for People Living with HIV and AIDS usually withless time to attend to hard physical work in the field. Theweed suppression by the cowpea canopy is consistent withSteiner, (1984) that intercropping maize with ground nut( Arachis hypogaea L.), mugbean (vigna radiate L.) or sweet potatoes(Ipomoea batatas L. Lam) reduced weed growth, yield losses and timerequired for weeding.

5.6 Partial budgetingCrop production may not be useful if it does not improveincome for the farmer. Inter cropping among the systems usedresulted into highest production cost. The high costs fromthis system were mainly because of added cost to producecowpea as an intercrop. The extra costs were from cowpea seedpurchase, pest control, planting and labour to harvest andprocessing the cowpea grain. Despite high costs in theintercrop, the net income was found highest for this system.Weeding once, therefore, in the intercrop, proved mostprofitable due to less labour required for weeding andincreased maize yield. The outcome of the study was supportedby Mdita et al., (2008) who confirmed a higher significant netincome from the maize –soyabeans intercropping system than insole cropping.

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6.0 CONCLUSION From this study it can be concluded that:1) At small holder farms in Zambia, it is possible to produce

sufficient maize yields by controlling weeds with cowpeacover crop that suppresses weed germination and growth asinter crop in maize crop.

2) Weeding only once in the maize –cowpea intercrop yieldedmaize grain similarly as weeding two or three times in solemaize crop. Weeding once in intercrop showed labor savingfor a farmer of 44% by weeding two times and 62% by weedingthree times. The inter cropping farming system, therefore,contributes to labour saving technologies required by thepeople living with HIV and Aids because saved labour wouldbe used to conduct other profitable activities or take careof the patients

3) Significant Low maize yield in sole maize crop weeded onceentails that farmers should not attempt weeding one time intheir fields of maize crop. This is because the low maizeyields reduce net benefit by 23% in the sole maize cropcompared to total benefit obtained from maize and cowpeayields in the intercrop weeded once. Farmers who practicessole maize cropping can increase yields through weeding morethan one time but it is costly on labour.

4) The Land Equivalent Ratio of 1.97 between the sole croppingand intercropping of maize and cowpeas was significantlyhigh, hence intercropping is the most beneficial system thatshould be promoted among the small holder farmers.

5) Cowpea cover crop has strong ability to inhibit germinationand growth of grasses, commelina and sedges species. Amongthe broad leaved weeds, Richard scabra, Trycodesma zeylanicum andAgerantum conyzoides are the most sensitive weeds species tocowpea canopy shading and allelopathic effects. Cowpeacover crop does not inhibit the germination but can reducethe growth rate of 70% of the broad leaved weeds under thecanopy.

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The study, however, had its limitations. The first one is thata trial was unable to identify particular broad leavedspecies whose growth under the canopy was reduced butincreased in weed numbers. The study therefore should becontinued to seriously check on the suppressed weed species atminimum of three different locations.

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