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    About UTA . . .The International Institute of Tropical Agriculture (IITA) is an autonomous, nonprofit corporationgoverned by a I5-memb er board of trustees headed by Dr . John J. McKelvey Jr. of th e United Statesof America. The Tnstitute's chief executive officer is Director General Dr . Ermond H. Harrmans.

    l ITA seeks to develop alternatives to shifting cultivation that will maintain the productivity of theland under continuous cultivation in the humid and subhumid tropics; to develop higher yieldingpest an d disease resistant varieties of cowpeas, yams an d sweet potatoes worldwide, and of maize, rice,cassava and soybeans in Afril:a, and to strengthen national agricultural research systems by acomprehensive training program and collaborative research.

    l ITA was established in I967 hy the Ford and Rockefeller Foundations, which provided th e initialcapital for buildings an d development, an d the Federal Military Govern ment of Nigeria, who allotted1 ,000 hectan:s of land for a headquarters site seven kilometers north of Ibadan.

    l ITA is one of 13 nonprofit international agricultural research an d training centers supported bythe Consultative Group for International Agricultural Research (CGIAR). The CGIAR is supportedby th e Food and Agriculture Organization of th e United Nations (FAO), the International Bank forRec..:onstruc..:tion and Development (World Bank) and th e United Nations Development Programme(UNDP). The CGIAR consists of about 50 donor c..:ountries, international and regional organizationsan d private foundations.IITA receives support through th e CGIAR from a number of donors including Australia,Belgium, Canada, Ford Foundation, France, Federal Republic of Germany, India, World Bank,International Fund for Agricultural Development (IFAD), Italy, Japan, The Netherlands, Nigeria,Norway, Organization of Petroleum Exporting Countries (OPEC) Fund for AgriculturalDevelopment, United Kingdom and the United Statcs of America. In addition, other donors providefunds to l ITA to support specific research an d training programs.

    Cover: Exper imental field to study the effects of hedgerow heightand time of pruning on crop yield.

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    ALLEY CROPPINGA Stable Alternativeto Shifting Cultivation

    By

    B.T. KangSoil Scientist

    G.F. WilsonAgronomist

    T.L. LawsonAgroc limatoiog isl

    ln tcrnationalln stirute of Tropical AgricultureOyo Road, PMB 5320, Ibadan, Nigeria

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    ForewordIn most parts of he tropics, especially in tropical Africa, thereis a critical need to increase food production to meet thedemand of a rapidly increasing population.

    On e of the challenges presented to the InternationalInstitute of Tropical Agriculture from its beginning hasbeen to develop alternatives to the centuries-old shiftingcultivation and bush fallow production systems predominantin tropical regions. Such traditional systems are effectivegiven an unlimited amount ofland and labor. Th e fertility andproductivity of tropical soils have been maintained by shortperiods (I to 3 years) ofcultivation followed by long periods ofrestorative fallow (bush).Problems arise when the supply of land and labor areno longer unlimited; when rapidly growing and rapidlyurbanizing populations pu t new and heavy demands on thefood production system.

    On e obvious response is to increase the cropping periodan d decrease th e fallow period, keeping more land undercultivation at a given timt!. Bu t this is not as simple as itappearS. The fragile tropical soils do no t respond well totemperate climate farming methods based on the use of heavymachinery and expensive agrochemicals, which often leave

    the land in poorer condition than does a heavily used bushfallow system. In an attempt to incorporate the good featuresof bush fallow into a continuously productive farming system,scientists at !ITA have developed a production system fortropical agriculture called allt!y t.:ropping. This is an agroforestry system that involves growing food crops in alleysformed by hedgerows of leguminous trees or shrubs.

    This exciting new development of integrating the ar t orknoWledge developed over the centuries by the small tropicalfarmer with modern science or technology} we believe, hastremendous potential for feeding the increasing populationsan d simultaneously stabilizing tropical soils for futuregenerations.!ITA scientists B.T. Kang, G.F. Wilson and T.L. Lawson,who pioneered this concept eight years ago and carefullyresearched its many phases, have prepared this technicalbulletin for the information of scientists, teachers, techniciansan d farmers.Ermond H. HartmansDireCtor GeneralInternational Institute of Tropical Agriculture

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    IntroductionIn many parts of the humid and subhumid tropics,particularly in Africa, shifting cu ltivation with therelated bu sh-fallow slash-and-burn cultivation is st illthe dominant food crop production system. In thissystem short (one to two years) cropping periodsalternate with long (six or mo re years) fallow periods.This fallow restores soil ferti lity and rids the land ofmany noxious weeds, pests and diseases. A large area ofthe humid and subhumid region is dominated by lowactivity clay (LA C) soils. The se soils are characterizedby low effective cation exchange capacity, low availablewater and nutrient reserve, and are highly susceptible tosoil erosion (Kang and Iuo, 1981).

    The restorative power of the bu sh fa llow is linked tothe regrowth ofdeep rooted trees and shrubs that recycleplant nutrients and build up soil organic matter (Nyeand Greenland, 1965). During the fallow period plantcover and Ii tter protect the soil from the impact of highintensity raindrops and the roots help to bind the soils,increase water infi ltration and reduce runoff and soilerosion. Moreover, litter mulch and shading by tree andshrub canopies reduce soil temperature and maintainsoi l moisture conditions that are favorab le for thegrowth of beneficial soil macro- and microorganisms .'The humid zone is defined as areaswith precipitationequal to orgreater thanpotential evap otranspiration for six [ 0 eight months of the year. In thesubhumid zone, precipitation is equal to or greater rnan potentialevapotran spiration for fo ur to five months of th e year.

    Figure 1. Traditional farm plot near Onne in southeastern N igeriashowing mixed cropping of maize an d ya m growing onnewly cleared land after 7 years of bush fallow. In-situgrown Am liollala macrophylla stakes are used for stakingyam.This shading also reduces weed infestation .

    In addition to restoring so il fertility, the bush fallowprovides supplementary food , animal feed, stakingmaterial, firewood and herbal medicine (Okigbo, 1983).Where land is abundant the bush fallow has beenfound to be a stable and efficient biological method forsoil productivity restoration. Food crops grow well onnewly cleared land following a long rest period un der

    bush fallow, as illustrated in the example from south-

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    Figure 2. Alley cropping maize with Leucae l/a Iwcocepllala at UT A .

    eastern N igeria shown in Figure 'r.In creasing land pr ess ure, resulting from rapidpopul ation growth in many part s of th e tr opics, hasresu lted in a shortening of th e fallow periods, Over-exploitation of land dominated by highly wea th ered

    kaolinitic soils can easily lead to soil degradation, arapid decline in crop yield and invasion by noxiousweeds, including difficul t to cont rol grass species .Since farmers in many develop ing countri es in the

    tr opics cannot afford cos tly inputs, it is necessar y to2

    develop a low input so il ma nagement technology tbatcan sustain crop product ion . On e promising techniqueis alley c ropping.T his bulletin desc ribes th e basic principles andresults of six years of alley cropping research cond uctedmainly at th e In ternational In stitute of Tropica lAgr icultu re (II TA) in Ibadan, N iger ia .

    The Alley Cropping Food ProductionMethodAlley cropping is essentia lly an agrofores tr y system inwhich food crops are grown in alleys form ed byhedgerows of trees or shrubs (Kang et ai" 1981b;Wilson and Kang, 1981). The hedgerows are cut back atplanti ng and kept pruned during cropping to preventshading and to redu ce comp etition with food crops (F ig.2). When there are no crops , the hedgerows are allowedto grow freely to cover th e land.Alley cropping retains the basic featu res of bu shfa llow. I t can easily be adopted by resour ce-poorfa rmers in the tropics , Trees and shrubs in th e aileysys tem : Provide green manu re or mulch (Fig. 3) fOr"comp anion food crops. In this way plant nutrientsare recycled from deeper soil laye rs, Provide prunings, applied as mu lch, an d shade

    during the fa llow to sup ress weeds.

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    Figur e 3. Mulch cover from Acioa ba rteri; prunings.

    Prov ide favo rable conditions for so il macro- andmicroorganisms. When planted along th e contours of sloping land ,p rov ide a barr ier to contro l so il erosion. Prov ide prunings for b rowse, staking material and

    firewood . Provide biolog ically fixed nitroge n to the compan

    IOn crop .3

    The majo r advan tage of a lley cropping over th etraditional shifting cultivation and bu sh fallow sys tem sis th at th e cropping and fa llow ph ases can take placeconcurr ent ly on the same land, thus allowing the farm erto crop for an ex tend ed period w ithout returning th eland to bu sh fa llow.

    Tree and Shrub SpeciesA number of trees and shrubs are po tentia lly sui ta ble foralley cropping, but onl y a few have been tested . T reesand shrubs tested so far include the leguminous speciesL eucaena leucocephala, Gliricidia sepium, Flemingiacongesta an d th e nonleguminous spec ies, A lchomeacord,jolia, A cioa barterii and GlIleLina arborea. T heimpor tance of some species in soil fer tility regenerationin the tr adi t ional bu sh fallow has been recogni zed byfarmers in many part s of the tropics as evidenced byth eir select ive retent ion of these species in the fa llow. Inareas of high popu lation densi ty , se lective retention ha sres ul ted in fewer species being left in th e bush fallow(Ob i and T uley, 1973). In several areas of southeasternNigeria , for example, where th ere were norm a lly manyspecies in the natu ral fallow , only four species arenow predominant , Alchomea cordi/olia, Acioa barter i,Anthonata macrophylla and Dialiumgllineense (T able 1).

    T o evaluate and select sui table tr ee and shrub speciesfor a lley cropping, field tes ting is curr ently being

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    Table I . Vegeta tion de nsit y of three- and seven-year-old bushfallow in so utheas tern Nigeria (Getahun er al., 1982)AKWA IKOT-EKPENE3-year 7 - y ~ a r 3-year 7-yearSpecies Density/ha (% )

    Dialium guineeme 48.8 41. 0 0.8Amhonaca macrophylla 270 34.6 53-4 337Pemaclelhra macrophylla 2-4Acioa barterj; J27 239 36A/chomea cordifo/ia 95 05 153 51.2Nape/jona imperia/is 36Unkn own 30.5 7.8Total 100.0 100.0 100.0 999Total plants/ha 1,008 1,5 0 4 1,0 4 8 1,3 28

    conducted on Alfisols (pH- 5.6) at IITA in rbadan (Fig .4) and also on acid Ultisols (pH - 4.5 ) at IITA's highrainfall sub station near Onne in southeastern Nigeria.Trees and shrubs sui tab le for alley cropping shouldmeet most of the following criter ia : Can be establi shed easily Grow rapidly Have a deep root sys tem Produce heavy foliage Regenerate readi ly after pruning Have good coppicing ability

    Figure 4. Field testing tree and shrub species for suitability foraUey cropping with food crops at I1TA.

    Are easy to era dicate Prov ide useful by-productsLeguminous trees and shrubs, because of their abilityto fix atmospher ic nitrogen, are preferred over nonlegumes.

    Few species meet all of th e above-mentioned criteriaand some have disadvantages that mu st be overCome.Leucaena , for example, has slow early growth, and itsseedlings mu st be protected against weeds during early

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    establishm ent. But once established, leucaena seedlingsgrow vigorous ly.Multipurpose sp ec ies are generall y preferablebecause they give the alley cropping sys tem flexibility.Occasionally it may be necessary to choose a species thatis excellent for a specific purpose - for example, Acioabar!erii for its slow decomposing mulch or th e fastgrowing Calliandra calozhy.-sus for its ability to producea large amount of firewood within a short time (NAS,1983)Establishment of Trees and ShrubsDirect seeding is the easiest and cheapest method ofestablishing hedgerows. Seeds carried in pockets orsmall bags can be planted by hand or with simpleplanters . However, seed lings from direct seeding areusually very small during early development and mu stbe given extra care and protection.A cheap and easy way of establishing leucaenahedgerows is by direct seeding in the same row with acrop such as maize (Fig. 5). With thi s method ofestablishment, there is no extra weeding cost for theleucaena during early growth. The slower growingleucaena can also benefit from residual fertilizer appliedto the maize crop . At the time of maize harvest, theleucaena has normally reached a height of 750 cm (Table

    Figure s. LellCQwa lellcocephala established with a maize crop atharvest time.

    5

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    Table 2. Height and diameter of Leucaena leucocephala establishedwith maize and maize/cassava after maize harvest (G. F.Wilson, unpublished data).Cropping systemMaize/leucaenaMaize/leucaena/cassavaLeucaenaLSD 0.05

    Heigh' (em )37537044574

    2) and is able to outgrow the weeds.

    Girth (em)2722.623.140 . 25

    Seeds of certain legumes, such as leucaena, requirescarification for good germination. Scarification can bedone manually or by hot water or acid treatments. Thehot water treatment is frequently used. This is done byimmersing the seeds in four to ten times their volume ofhot water (90C) and allowing them to soak in thegradually cooling water for 12 to 24 hours. Thistreatment can give erratic results . Acid treatment is amore reliable method of scarification . Seeds are treatedfor 60 minutes with concentrated (commercial grade)sulphuric acid (98 % , 36 N) at a seed to acid ratio ofabout 10 :1 by volume. Following treatment the seedsare immediately rinsed in running water to removetraces of acid.

    Transplanting is used when direct seeding does notgive desirable results or for seeds that rapidly lose theirviability during storage, as do the seeds of Acioa barterii.Seedlings grown in nursery beds are transplanted as6

    bare root seedlings. Those grown in perforated plasticbags are transplanted with the bags, or the bags areremoved at transplanting . Bagged seedlings, however,are bulky, difficult to transport and thus expensive tohandle. Generally, the seedlings are tall enough to have acompetitive edge over weeds and require less care andprotection during early development.Cutting is an alternative method for establishing somespecies, bu t it is only recommended when direct seedingis not feasible. Fo r example, gliricidia can be establishedby direct seeding, bu t woody cuttings 50 cm or more inlength often give better results.Soil and climatic factors are important for successfulestablishment. Leucaena and gliricidia, for example,establish well in non-acid soils with adequate annual

    precipitation. On strongly acidic soils, soil amendments,particularly phosphorus and lime, are needed for goodgrowth of these species. Inoculation with compatiblerhizobium strains is sometimes necessary for rapidestablishment.

    Alley WidthFour meters between hedgerows is quite satisfactory forcontinuous food crop production with or without theuse of a tractor. However, if the purpose of alleycropping is to provide in-situ staking material for a yamcrop, the spacing should be adjusted to suit the yam

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    First SeasonEstablishment of ~

    First SeasonLeucaena hedQerow pruned

    YEAR /Second Season

    Hedgerow

    YEAR 2Second SeasonLeucaena hedgerow prunedyield mulch, green manureand stokes

    Dry Season

    HedoerON

    Figure 6. Cropping sequence diagram for establishing Leucaena leucocephala hedgerows (spaced 4 m) fo r alley cropping with sequentiallycropped maize an d cowpeas.7

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    YEAR/First Season

    1-2m.--I

    YEAR:?First Season

    YEAR3First Season

    Figure 7. Cropping sequence diagram fo r establishing Leu caenaleucocephafa hedgerows (spaced z m) for aUey croppingmaize and for in-situ ya m vine support.

    8

    spacing. Figures 6 and 7 show leucaena alleys with 4-mand 2-m interrow spacing. The latter has been used forin-situ yam staking.

    Within the hedgerows, trees and shrubs can be spaced25 to 100 cm apart depending on the species.PruningDuring cropping, pruning of the hedgerow is necessaryto avoid shad ing of the companion crop. Table 3 showschanges in the percentage of incoming light (globalradiation) incident on alley cropped cowpeas befor e andafter pruning of the leucaena hedgerows. Results of thisand various other experiments carried out at IITA inIbadan show that pruning heights of 25 to 75 cm aresatisfactory. East-west orientation of the hedgerows alsominimizes shading .Table 3. Percentage of daily global radiation (RG) incident oncowpeas alley cropped with LeucaellQ leucocephala before an dafter the pruning of hedgerows (T.L. Lawson, unpublisheddata) .

    Season2nd, 1982

    Period/timeBefore pruningAfter pruning

    Percent radiation eRG )incident on the cowpea cropW* M* E* Mean4189

    4990

    5792

    W and E refer to the west and east sid es of the plots, close to the Jcucaenarows, which are 4 m apart and orientated north-south ; M refers to themiddle of the plot, midway between the leucaena rows.

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    Pruning can be done manually using a sharp cutl ass orslasher (Fig. 8). A dull curlass or slasher that strips thebark wi ll delay coppicing and result in the death of theplants. Fo r pruning large plots, Howard rotary bladeshave given good results. This implement can cut backone hectare of one-year-o ld leucaena hedgerows spaced4 m apart in about one hour. Small, 21--horsepowerbackpack brush cutters have also given satisfactoryresults for pruning of uniform size plants with ad iameter of less than 3 cm . I t requires approx imatelyeight hours to prune one hectare with brush cutters.

    Pruning intensity varies with the shrub or treespecies. As a general rule, th e lower the hedgerows andthe taller th e crop, th e less frequently is pruning needed .Fa st growing plants, such as leucaena and gliriciaia,require pruning every five to six weeks during cropping.To o low and roo frequen t pruning of th e hedgerowsshould be avo ided as it ma y result in die back.

    Staking for Vine SupportAn added benefit of alley cropping is th at stemsproduced by trees and shrubs grown in th e hedgerowscan be used for suppor t ing climbing plants such as beans(Rachie, 1983) and yams (Wilson and Akapa, 1981 ).Major meth ods of using th ese stems are: In -situ live staking: Live stems serve to support

    nearby climbing plants . Figure 7 illustrates an alley9

    Figure 8. Pruning L e I/ COellO leucocephala hedges.

    cropping rotation betwee n maize/Jeucaena andyam jleucaena . At the start of yam growth, the stemsare cut back to a height of about 2.0 m to keep themwithin reach for pruning. A major disadvantage ofthi s meth od is th e difficulty of pruning the leucaenastem when tbe yam vines reach the rop of the ste m. In -si tu dead staking: T he stems are killed close totbe gro und eith er with fire or by girdling and used assupport for th e climbing crop planted d ose by.

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    Cutting back is unnecessary, and the climbingplants can grow higher for better leaf exposure.

    Cu t and carry staking: Th e stakes are cu t and usedouts ide the alley cropping area. Th is method isfavored by farmers who are current ly testing alleycropping in the yam growing area of east centralNigeria. This work has led to the development ofstake lots in which a fast growing tree, such asleucaena, can be planted more densely than in alleycropping for the sole purpose of producing stakes.Stake lots can be established on marginal land.

    TillageConventional tillage involving plowing and harrowing isnot required . Whether tillage is used or no t makes on ly asmall difference in the yield of the alley crop as long asthere is adequate mulch from the prunings (Table 4):However, occasional shallow tillage between thehedgerows that will partially trim the surface roots of theshrubs or trees is recommended.Weed ControlThe control or suppression of noxious weeds, a majorfunction of the bush fa llow, is also a major attribute ofalley cropping. Shading by trees or shrubs during thefallow suppresses most weeds. Th e prunings, applied asmulch, also suppress weeds. Weed growth after arotation of maize followed by one year of naturally

    12

    Table 4. Effect of tillage and no-tillage on yields of sequent ia llycropped maize and cowpea grown on Apomu loamy sa nd(Psammentic Ustorthent) in a lley cropping with LeltcaenaICltcocephala (B.T. Kang , unpublished data),Maize yield Cowpea yield(main season) (min or season)

    Treatment (tons lha)N rate ' (kg N lha ) 1982 19 83 1982Tillage0 2.10 1.92 0.61

    40 2.67 241 04780 291 3. 16 048No-Tillage0 1.57 2.17 05340 2.29 3.03 05480 2 42 397 049

    LS D 0.05 0-44 079 0.15-Nitrogen applied only to the main season maize and not to the minorseason cowpea .

    1983

    0-450570-450. 5 00510-490.09

    regenerated fallow compared with that after one year ofleucaena (regrowth of hedgerows) fa llow shows thatmost weed species are suppressed by leucaena (Table 5).Although vo lunteer leucaena became the major weed inleucaena fallow, its adverse effect on maize yield was lessthan that of weeds from the short natural fa llow whereweeds were not controlled (Table 6).

    Prunings from Acioa barterii (Fig. 9) and Alchorneacordi/alia, which decompose slowly, are effective when

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    Re sidue ( t Iho)2 7 . 0 ' r - - - - - - - - - - - - - - - - - - - - - - - - - ~

    21.4

    15.8 10.2

    4 .6 -

    O ' L - - - ~ ~ ~ ~ - - ~ L - - - ~ - - - - ~0..0. 16.8 33 .6 50..4 67.2 84.0.Weeks after pruningFigure 9. Change with time in am ount of residual Acioa barten'iprun ings applied as m ul ch (IITA , ]98:z).

    Biomass production and nu trient recycling dependson factors such as plant species, spacing, soil and

    Table 7. Nutrient composition of prunings of four tree and shrubspecies grown on Egbeda sand y loam (Oxic Paleusta lf)(Koudoro, 198z).N P K Ca Mg

    (% )Gliricidia sepiu11l 4 2 1 0.29 343 1. 40 0 4 0Leu caena leucocephala 433 0.28 2 .5 0 1.49 0.36Alchonrea cordzfolia 3.29 0.23 1.74 046 0 .20A cioa barrerii 257 0. 16 1.78 090 0. 27

    climatic conditions (Guevarra el ai., 1978 ; Rac hie,1983). As shown in Tab le 7, prun ings from differentspecies exhibit large differences in nut rient composition.Among the four species studied, leucaena has thehighest nutrient concentration.Depending on the spec ies, pr unings from thehedgerows can also produce substant ial quantities ofstakes. Fully grown leucaena and gliricid ia hedgessequentially cropped with maize and cowpeas in theIbadan area and periodically pr uned back to a height of75 cm produce over 5.7 and 1.4 tons jha of dry weight ofstakes, respectively (Table 8). At Ibadan many of th estakes were prod uced during the dry season (Novemberto March) when there is no cropping and the hedgerowsare not pruned. Utilizing subsoil moisture during thefo ur-month dr y season, leucaena and gliricidiahedgerows grew 4.0 m and 2.5 m, respectively. Wh enallowed to grow uninhib ited fo r one year , the leucaena

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    Table 8. Dr y weight of usable stakes ( > z m length ) from pruningsof Lellca el/Q leucocephala and Gli,.icidia sepiltlll all ey croppedwith maize and cowpea on Egbeda sandy loam (OxicPaleustalf) (B.T. Kang, unpublished data).

    Hedgerow spacing2m4 mLSD 0.05

    Dry weight stakesGliric idia Leucaena(tons/haffive pruningsfyea r)

    0.86

    hedgerow easily reached a height of over 7.5 m and produced more than 88 tons of wood per hectare (Fig. 10).Effect on Soil PropertiesSix years of alley cropping leucaena with maize andcowpeas on a low fertility Entisol has given veryencourag ing results. Periodic addition of leuca enaprunings helped to maintain higher so il nutrient andorganic matter content (Table 9). Plots receivingprunings contained twice the amount of soil organicmatter as plots where prunings were removed. Repeatedapp lication of nitrogen fertilizer increased so il acidity,but the add ition of leucaena prunings did not affect so ilacidity.Plots receiving leucaena prun ings also maintainedhigher soil moisture status (Fig. I I ) . Mulch from

    J 5

    Figure 10 . Lel/cae lla leu cocephala prunings as source of firewood.

    Table 9. Effect of s ix years ofaUey cropping maize and cowpea withLel/cae lla /eucoceph ala and nitrogen application on somechemical properties of surface soil of Apomu loamy sand(Psammentic Ustorthent) (B .T. Kang, unpublished data ).Exchangeable Bray

    Treatments Leucaena pH- Org. C K Ca Mg P- I(kg N/ha) prunings H, O (0) (me/ loog) (ppm)0 Removed 6.0 0.65 0.19 2 .9 0 035 27 . 00 Retained 6.0 1. 0 7 0.28 3-45 0 .5 0 26.280 Retained 58 1. 19 0.26 2.80 0 -45 256LSD 0.05 0.2 0. 14 0.05 055 0. 11 53

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    Soil moisture content (%)

    10

    5

    (+ R) Mulching with leucoeno, pruning,,,,,,,~ ....

    ~ " ' - - - ~. / ~ ,(- R) No mulching .. .......

    O L - - - - - ~ - - - - - L - - - - - L - - - - ~o 10October 20 30NovemberFigure II. Soil moisture content of Apomu loamy sand(Psammentic Ustorthent) sampled at 5-J5 em depthfrom plots receiving leucaena prunings ( +R) an d noleucaena prunings ( - R) (H. Grimme, unpublisheddata).

    16

    prunings lowered so il temperature an d enhancedbiological (particularly earthworm) activity.

    Crop PerformanceThe recycling of nutrients to the surface soi l is one of thebasic assets of alley cropping. Where nitrogen-fixingleguminous trees or shrubs are used, some of thenitrogen fixed is eventually released to the companioncrops through decomposition of prunings (leaves andtwigs ).

    It ha s been observed (Kang et aI., I98Ia ) that leucaenaprunings are a more effective nitrogen source whenincorporated in th e soil than when applied as mulch(Table 10). The better results obtained with in-corporation may be due to faster decomposition andmineralization of prunings (Fig. I2 ) . Buried in the soil,fresh leucaena prunings have a half-life of less than 10days. The lower efficiency of surface applied pruningsma y be due to high losses from N volatilization duringdecomposition (A. D . Messan, pe rsonal communi-cation). The high nitrogen efficiency obtained withincorporat ion may not always be desirable or practical ,especially where other benefits can be obtained byapplying th e prunings as mulch.

    Desp ite the high nitrogen yield from the prunings ofleucaena hedgerows, the benefit fro m the nitrogenadded with the prunings to th e food crop was less than50 % (Guevarra et ai., 1978 ; Kang et ai., I98Ia). Even

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    Percent of sample remoining undecomposed

    100

    80

    60

    40

    20

    LSD (.05)I\\

    I I I I I"" \\\

    " / Dry leucoena applied at soil surfacet..--- ___ .... ,, ~ - - - . - : }'b... ... ..tFresh leucaena app lied at sail surfaC4l.... " ( ) . . ~ - --- --

    ry leucaena buried

    Fresh leucaena buried

    oL-_____ l______ _____ l____o 20 40 60Days in field

    Figure 12. Decomposition of fresh and dry leucaena pruningsapplied as mu lch or buried in soil (Read, 1982).

    ' 7

    Table 10. Effect of applications of Leucaula leucocephala prunings andinorganic nitrogen on grain yield of maize grown onApomu loamy sand (Psammentic Ustorthent)(Kang et al.) 1981a)Leucaena pruningsLeucaena rate N rate Incorporated Mulch(tons/ha ) (kg N /ha) (grain yield/kg/ha )

    0 0 1283 174050 2093 2218lOO 33 15 3138

    5 0 23 13 20 1350 3035 2300100 3453 302810 0 32 13 185550 2578 233 8100 3068 302 3Mean 2705 240 6LS D 0.05 Between means of methods of leucaena placement, 688.Between treatments in different leucaena placementmethods, 1146 .

    so, the amount of nitrogen utilized was a significantportion of the crop requirement (Fig. 13 ). Fo r maize,relatively low rates of additional fertilizer nitrogen wererequired for obtaining optimum yield. On a sandyEntisol at Ibadan, yie ld of maize alley croppedcontinuously for six years has been maintained at about2 tons/ha with the addition of leucaena prunings only(Table II ).

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    Ta ble I I . Main season grain yield of maize variety TZPB alleycropped with Leucaella lellcocephala on Apomu loamy sand(Psammentic Ustorthent) as affected by application ofleucaena prunings and nitrogen (B.T. Kang, unpublisheddata)Year

    N rate Leucaena 1979 198o 1981 * 1982 1983(kg N /ha ) prunings (Ions /ha )

    Removed 1.04 0-48 0.61 0.26 Retained 2.09 1.91 1.21 2.10 1.9280 Retained 3,54 3,26 1.89 291 3,16LS D 0,05 0,36 0.3 1 0.29 0,44 0,79*Maize crop seriously affected by drought during early growth.

    Table 12 . Main season grain yield of maize variety TZPB and seedyield of minor season cowpea variety VITA-6 alleycropped with Gliricidia sepiulII grown on an Alagba sandyloam (Oxic Paleustalf) at Ikenne in southern Nigeria(B.T. Kang and G.F. Wilson, unpublished data).

    Treatment Gliricidia Maize l Cowpea:!N rate (kg N /ha) prunings (kg/ha ) Removed 2699 Retained 33740 Retained 3 ~ 9 180 Retained 3125

    LS D 0,05 427'N - applied to main season maize.

    ~ C o w p e a plantings follow ing maize ip minor season and received no Napplication.

    73 8818820994187

    18

    With low intensity cropping on an Alfisol, in whichmaize was alley cropped with leucaena only in alternateyears, maize grain yield exceeded 4,0 tons /ha with theaddition of leucaena prunings only,

    Invest igations on Alfisols and Entisols in southernNigeria have shown that cropping maize and cowpeassequentially with either leucaena or gliricidia is apromising alley cropping system , Studies conducted onAlfisols at Ikenne (Table 12) and at Ibadan (Tables 13and 14) with maize alley cropped with gliricidia showedthat at both locations gliricidia prunings met th enitrogen requirement of maize , Cowpeas grown follow-Table 13. Effects ofaUey cropping and fertilizer application onyield of maize and cowpea grown on Egbeda sandy loam(Oxic Paleustalf) (G.F. Wilson, unpublished data).

    Maize yield Cowpea yieldNo F + P M ean No F Res.F Mean

    SpeciesNarural regrowth(contro l)Acioa barter!!Glil'icidia sep iumMean

    2,83,24A3,5

    4,44 ,55,24,7

    (tons /ha)

    3,6 0,84 0.81 0,83H 0,63 0.62 0,634,8 0,63 0,78 0.7 1

    0.70 0,74LS D 0.05 For maize yield: between species, 1.1 ; between fertilizer

    means, 0.8; between fertilizer within species, 1.4 and ,between fertilizer among species, 15.For cowpea yield: differences insignificantI ( + F), fertilizer applied to maize only: 60 N-60P O s - 6 0 K 2 0 in kg fha

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    Ma ize grain yield ( t / ha )6 .0

    5.0

    4.0

    3.0

    2.01.0o

    LSD.05~ Main season_ Minor season

    ON ON 40N SONLeucoena + +prunings removed 30 N 60 NNitroQen rate ( kQ/ha)Figure 13. Grain yield ofmaize alley cropped with Leucaenalellcocephafa grown on Apomu loamy sand (PsnmmcnticUstorthe nt) as affec ted by app lication of Jeucaenaprun ings and ni trogen (ma in season variety TZPB;minor season variety TZE ) (Kang et af' J (98th) .

    '9

    Figure 14. Alley cropping with Gliricidia sepill lll ,ing mai ze in alley cropping with gliricidia (Figure 14 andTable 12) required no fertilizer app lication .The potential of alley cropping pluvial rice and rootand tuber crops with leucaena and gliricidia is current lybeing inves tigated. Very promising results wereobtained from alley cropping cassava with gliricidia(Table 14 ) and also from alley cropping of pluvial riceand ya ms with leucaena on Alfisols.Planting leucaena hedges along contours is reportedto contro l soil erosion (Pru ssner, 19 82). T hus, alleycropping may be a suitab le food crop production

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    Table 14. Yield of maize and cassava alley cropped wiIh Gliricidiasepium and grown on Egbeda sandy loam(Oxic PaleustalO (G.F. Wilson, unpublished data) .Prunings app lied Prunings incor-Control as mulch porated in soilNitrogen rate

    (kg N/ha) Maize Cassava Maize Cassava Maize Cassava(tons/ha )

    0 2.II 23.04 2.36 25.46 2.76 227945 2.69 2437 2.70 2967 2.82 232690 291 25. 18 3. 0 1 31.62 303 29.07LSD 0.05: Maize, 0. 45 j Cassava, 6. 12

    method on slop ing land where soil erosion is a seriousproblem. The potential of using alley cropping for largesca le food crop production on sloping land is currentlybeing investigated .

    FodderAlley cropping was originally developed to maintain so ilfertility for food crops. However, where the hedgerowspecies are suitable for fodder , an animal comp onent(e.g., small ruminants ) cou ld be introduced into thesystem . The hedgerow species are usually leguminoustre.es or shrubs which provide high protein fodder. Forexample, leucaena and gliricidia fodders are well knownfor their high protein content.

    20

    The Small Ruminan t Programme of the In ternationalLivestock Centre for Africa (ILCA) has recognized thepotential of this system. Collaborative research betweenIITA and ILCA on the in tegration of crops and smallruminant s in a comprehensive alley farming system arebeing conducted (Sumberg, 19 84). Leucaena andgliricidia used in such a sys tem have produced sufficientfodder for dry season home feeding (Fig. 15 ).

    Figure 15 . Feeding goats and sheep with leucaeDa prunings in acut-aDd-carry system (Courtesy of Dr. A.N. Atta-Krah,ILeA).

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    Summary and ConclusionsAlthough bush fallow and shifting agriculture provideson ly a sub sistence living, it is ecologically stable andtherefore suited to the tropical environment.Unfortunately, most programs for improving agriculture in the tropics have tried to remove components ofthe bush fallow system, replacing them with destabilizing temperate climate farming methods.Alley cropping is a stable alternative to the bushfallow system. I t retains the basic principles andcomponents of traditional agriculture while introducingimportant improvements. In the traditional system treesand shrubs are grown in a random mixture. But in alleycropping they are planted in an organized system, whichmakes possible continuous cultivat ion of food crops.Biological recycling of nutrients and soil conservation, suppression of weeds and rapid production ofby-products such as stakes and firewood are majoradvantages of alley cropping. Where firewood hasbecome scarce as a result of increased demand for landfor crops and livestock production, alley cropping oralley farming offers a means of combining crops and /orlivestock with firewood production.Research at lITA on alley cropping has led to thedevelopment of the following alley cropping systems: The leucaena/gliricidia maize-cowpea alley crop

    ping system.2 I

    The leucaena-maize-yam alley cropping system. By integrating leucaena and gliricidia alley croppingwith livestock production, ILeA ha s developedalley farming, a promising sma ll ruminant production system for the humid region of Africa.

    Intensive work with alley cropping has been done on thehigh base status or less acidic Alfisols and associatedInceptisols and Entisols. More research is in progress onthe low base status and acidic Ultisols. Suitable tree andshrub species (particularly legumes) have yet to beidentified. Promising species such as Gmelina arborea,Acioa barterii, Flemingia congesia, Alchornea cordi/oliaand other s are being tested on acid soils (TypicPaleudult) at lITA's high rainfall substation at Onne.As a biological low input production system, alleycropping should be a preferred production technique indeveloping countries where shortages of foreignexchange prohibits the importation or use of largequantities of inputs such as fertilizers and pesticides.ReferencesBrewbaker, J L., and Hutton, E.M. 1979. Leucaena -versatile tree legume. In New Agn"cultural Crops, AAASSelected Symposium, ed. G.A. Ritchie, pp. 207-259.Boulder, Colorado: Westview Press.Getahun, A., Wilson, G.F., and Kang, B.T. 1982. The role oftrees in farming sys tems in the humid tropics. In Agro-

    forestry illlhe African Humid Tropics, ed. L.H.MacDonald,pp. 28-35 Tokyo: United Nations University.

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    Guevarra, A.B., Whitney, A.S ., and Thompson, J .R. 1978.Influence of intra-row spacing and cutting regimes on th egrowth and yield ofleucaena . Agroll.] . 70: 1033-1037.International Institute of Tropical Agriculture . 1982. Use of

    A. barterii as a beneficia l mulch in alley cropping. ResearchHighlights, pp . 32-33 . Ibadan: lITA.Kang, B.T ., and Ju o, A.S .R. 1981. Management of lowactivity clay so ils in tropica l Africa for food cropproduction. Paper read at Fourth International SoilClassification Workshop , 2-12 June 1981 , Kigali, Rwanda .

    Kang, B. T ., Sipkens, L. , Wilson, G .F. , and Nangju, D.1981a. Leucaena (Leucaella le"cocephala (Lam) de Wit)prunings as nitrogen source for maize (Zea mays L ). Ferl.Res . 2: 279-287.Kang, B.T ., Wilson, G .F ., and Sipkens, L. 1981b. Alleycropping maize (Zea mays L ) and leucaena (L ellCaellQleucocephala Lam) in southern Nigeria. Plam alld Soil 63:165-179.Koudoro, D. 1982. HEvaiu3rion of four woody fallow speciesfor alley cropping with maize and cow peas." M. Sc. thesis,National Uni versity of Benin, Cotonou, Benin.National Academy of Sciences. 1977. Leucaena. PromisingForage and Tree Gl"Op fo r the Tropics. Washington, D.C. :National Academy Press.National Academy of Sciences. [983. Gallialldra. A VersatileSmall Tr ee for the Humid Tropcs. Washington, D .C.:National Academy Press.

    Nye, P.H., and Greenland, D.J. [965. The Soil Under ShIftingCultivation . Technical Communication 5 I . Harpenden,Eng land : Commonwealth Bureau of Soils.

    Obi , J. K ., and Tuley, P . 1973. The Bush Fallow alld LeyFarming in the Oi l Palm B elt of Southern Nigeria.

    2 2

    Mi sce llaneous Report [61. London: OverseasD evelopment Ministry.Okigbo, B.N. 1983. Plants and agroforestr y in land usesys tems ofW . Africa . In Plam Research ill Agroforeslry, ed.P.A. Huxley, pp. 25-41. Nairobi, Kenya: InternationalCouncil for Research in Agroforestry.Prussner, K .A. 19 82. Overcoming critical lands : examples inEast Nusa T enggara. National Leucaena Seminar I, 23-25August 1982, Jakarta, Indonesia.Rachie , K.O . [983. Intercropping tree legumes with annualcrops. In Plam Research and Agr%reS!ry, ed. P .A. Huxley,pp. I 03 - 1 16 . Nairobi, Kenya: International Council forResear ch in Agroforestry.Read, M .D. 19 82. "Management alternatives for maize-beanand leucaena-ba sed cropping sys tem s." Ph .D . the sis,Colorado State University, Fort Collins, Colorado.

    Sumberg, J.E . 1984. Small ruminant feed production in afarming systems context. Paper read at Work shop on SmallRuminants Production System s in the Humid Zone ofWest Africa, 22-26 January 1984, International Institute ofTropical Agriculture, Ibadan, Nigeria.Wilson, G.F., and Akapa, K. 1981. Improving the in-situstem support sys tems for yams . In Tropical Root Crops:Research Strategies/or the 1980s, ed. E. R. Terry e! al., pp.195-[97. Ottawa: International Development ResearchCentre.Wilson, G .F. , and Kang, B.T. 1981. Developing stable andproductive biological cropping sys tem s for the humidtropics. In Biological Hu sbandry: a Sciemljic Approach toOrganic Farming, ed. B. Stonehou se, pp . 193-203 .London: Butterworth.

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    AcknowledgementsThe authors wish to express their special thanks to Dr . A.S.R.Juo, Dr. P. Ay, Mr. J.E . Keyser, Mr. N . Russe ll , Dr . J .Sumberg, Mr . F .M . Gatmaitan J r and Prof. W .B. Ward fortheir in va luable criticisms) suggestions and assistance in thepreparation of this bulletin. Appreciation is also given [Q M s.A. Ukasoan ya for typing the manuscript.

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