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The Australian Centre for International Agricultural Research (ACIAR) was establishedin June 1982 by an Act of the Australian Parliament. Its mandate is to help identifyagricultural problems in developing countries and to commission collaborative researchbetween Australian and developing country researchers in fields where Australia hasspecial research competence.

Where trade names are used this does not constitute endorsement of nordiscrimination against any product by the Centre.

ACIAR PROCEEDINGSThis series of publications includes the full proceedings of researchworkshops or symposia organised or supported by ACIAR. Numbersin this series are distributed internationally to selected individuals andscientific institutions. Recent numbers in the series are listed inside theback cover.

Australian Centre for International Agricultural Research.G.P.O. Box 1571, Canberra, ACT 2601 Australia

Craswell. E.T. and Simpson, J. ed. Soil fertility and Climatic Constraints in DrylandAgriculture. Proceedings of ACIARlSACCAR workshop hcld at Harare, Zimbabwe.30 August I September 1993. ACIAR Proceedings No. 54. 137p.ISBN 1 86320 122 XEditorial management and technical editing: P.w. LynchCover: Classified image based on derived SPOT multispectral bands. March 1988,showing land cover types: Molepolole Village. Botswana. CNES.1988Distribution by SPOT Imaging Services, Sydney.Typesetting and page layout: Sun Photoset Pty Ltd, Brisbane. AustraliaIllustrations: BPD Graphic Associates, Canberra, AustraliaPrinted by: Watson Ferguson & Company, Brisbane, Australia


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Soil Fertility and ClimaticConstraints in Dryland AgricultureProceedings of ACIARlSACCAR Workshopheld at Harare, Zimbabwe,

30 August-l September 1993

Editors: E.T. Craswell and J. Simpson

Australian Centre for International Agricultural ResearchCanberra 1994


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ContentsForeword 5Overview of the current situation and previous impact of adaptive agricultural research

in southern AfricaStephen R Waddington 7Maize water use as affected by nitrogen fertilisation

Z. Shamudzarira 15The potentials and limitations of agroforestry for improving livestock production andsoil fertility in southern Africa

B.H. Dzowela and R Kwesiga 19Computer simulation models as management tools for sustainable use of naturalresources in highland-lowland systemsRN. Gichuki and H.P. Liniger 26Strategies for soil-water management for dry land crop production in semi-aridTanzaniaN Hatibu. H.R Mahoo. E.M. Senkondo. T.E. Simalenga, B. Kayombo andD.A.N. Ussiri 32

Modelling of maize growth and development in MalawiA.R. Saka, l.D.T. Kumwenda, P.K. Thorton, U. Singh and J.B. Dent 39Rates of adoption of new technology and climatic risk in the communal areas

of ZimbabweP. Huchu and P.N. Sithole 44

Management of soil fertility in climatically risky environmentsM.E. Probert, B.A. Keating, M.N. Siambi and l.R. Okalebo 51

Limitations to crop production in marginal rainfall areas of MalawiSA Materechera and H.R. Mloza-Banda 64

Constraints in the smallholder farming systems of ZimbabweE.M. Shumba 69

An integrated approach to soil fertility improvement in Malawi, including agroforestryJ.W. Wendt, R.B. lanes and O.A. ltimu 74

Economic and climatic risks in cropping systems in Chivi communal area, ZimbabweB.G. Mombeshora and M. Mudhara 80Recent developments in systems modellingPeter S. Carberry 84Linkages between Australia and Africa in agricultural research for the semi-arid

tropicsR.K. lanes 95

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Dealing with climatic risk in agricultural research a case study modelling maize insemi-arid KenyaB.A. Keating, R.M. WajUla, J.M. Watiki and D.R. Karanja 105Maize root profiles in gJeyic sandy soils as influenced by ridging and ploughingin ZimbabweH. Vogel 115Agricultural systems research in Africa and Australia: some recent developmentsin methodologyRL McCown and P.G. Cox 125

Working group reports and discussion 134

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ForewordAgriculture in Eastern and Southern Africa has to cope with unpredictable seasons,gradual loss of soil fertility, soil degradation, increasing pressures by human and livestock populations, and the restricted resources (cash. labour, and drought) of manyfarm households. Combined these produce stagnation or decline in productivity andreduce capacity to invest in improved management. The relative importance of thesefactors will vary between districts, depending on exact soil types, rainfall expectations,social/political issues etc, but the general syndrome is consistent and widespread. andindeed is shared by many farmers in dryJand areas of Australia. Definitive and comprehensive research providing clear and appropriate recommendations for better andsustainable management of the available resources is still urgently needed.

This volume records the proceedings of a workshop held to consider the problemsof dry land agriculture. The workshop was organised jointly by AClAR and theSouthern African Centre for Cooperation in Agricultural Research and Training(SACCAR) with three main objectives in mind:(a) to survey the commonality of problems facing small-scale farmers within thesemi-arid zones of the SADC region, and rccent research on those problems.including its possible development into techniques that are adoptable by farmers;(b) to present and discuss the findings of the recently completed ACIARlKARIproject in eastern Kenya (1984-93) which defined some new scientific approachesto analysing the feasibility of different management options for small-scalefarmers in semi-arid areas;(c) to examine the opportunities for increased research collaboration between theSADC countries, Australia and the International Centres.

The sixteen papers recorded in these proceedings were presented before anaudience of some 40 participants and several local observers in the first two days ofthe meeting. Agricultural researchers residing in Zimbabwe plus the Australian groupmade up the bulk of the audience. Other SADC countries (Malawi, Tanzania) andKenya were well represented. The meeting was opened by the Australian High Commissioner in Harare, His Excellency Mr J Thwaites. Researchers from InternationalAgricultural Research Centres (CIMMYT, IBSRAM, ICRAF, ICRISAT, IFDC. IFPRIand ILCA), and from the African Centre for Fertilizer Development and the WorldBank, Harare, also took part. Their participation was especially appreciated.

Particularly valuable was the discussion on the third day which was spent inworking groups and in plenary sessions to formulate recommendations on futureresearch in semi-arid areas of southern Africa. Opportunities for research collaborationat national, regional and international levels were explored and the outcome issummarised at the end of this proceedings.ACIAR acknowledges with sincere appreciation the cooperation and help of severalgroups. The enthusiasm and support of Dr M L Kyomo, Director of SACCAR, wasessential. In Harare, an informal committee comprising the Director of Research,Mr R J Fenner. the acting Head of Agronomy, Mrs D. Hikwa (both of the Department

of Research & Specialist Services) and Dr S R Waddington of CIMMYT, guided theearly organisation of regional contributions. Staff from the Australian High Commission in Harare helped with preparations for the meeting. Local knowledge andenthusiastic help with all the detailed arrangements by Ms Judith Ward was especiallyvaluable. Finally I want to thank Ms Maureen Kenning of ACIAR CommunicationsProgram who helped prepare the proceedings for publication.G H L RothschildDirectorACIAR

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Overview of the Current Situation and Previous ImpactofAdaptive Agricultural Research in Southern Africa

Stephen R. Waddington*Abstract

This paper appraises the contribution made by a decade of Fanning Systems Adaptive Research(FSAR) to the improvement of productivity in smallholder cropping systems of southern Africa,with emphasis on the management of soil fertility and climatic risk in maize.FSAR programs in southern Africa have been successful in diagnosing production constraints inmaize crops and in developing relevant new research opportunities to overcome those constraints.

There are also many examples where FSAR has successfully modified technology to featurereduced inputs at levels suitable for smallholders, adjusted management to fit smallholder circumstances and operational constraints, or introduced methods that enable fanners to move towardknown ideal practices, but few have led to significant adoption of adapted technology by smallholder farmers.Technical reasons for this modest impact from FSAR include over-reliance on 'fine tuning' ofexisting technology (often appropriate technologies from commodity or disciplinary research didnot exist for semi-arid areas), and shortcomings in the conduct of FSAR, such as excessiveemphasis on site-specific on-farm trials of conventional design coupled with standard analysis andinterpretation of results.The closer integration into FSAR of (a) plant improvement (to develop genotypes more efficientin their use of water and mineral nutrients), (b) crop modelling (to help focus on suitable tech

nology combinations and assess climatic risk), and (c) geographic information systems (to targettechnology to specific agroecological areas or groups of farmers), along with the incorporation ofa longer-term natural resource management perspective, will lead to a more robust researchapproach that better addresses the technology needs of smallholders.

BackgroundCharacteristics of smaJlholder farms and maizebased cropping systemsThe vast majority of farm households in southernAfrica use their own resources, especially familylabour, to produce crops (and often livestock) on 0.5-10 ha of land held under traditional tenure arrangements. Since most smallholder farmers do not ownthe land they farm, they lack collateral for commercial loans to purchase inputs and generally rely onassistance through government schemes. In largeparts of the region, particularly southern Zambia,"'International Maize and Wheat Improvement Centre(CIMMYT) PO Box MP 163, Mount Pleasant, Harare,Zimbabwe

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Botswana and much of Zimbabwe, animal (mainlyoxen) traction is used to prepare the land and helpweeding, while in Malawi, northern and easternZambia, and northern Mozambique human labourusing hand-held hoes is the predominant powersource.

Generally. maize exceeds 60% of the total smallholder crop area in sub-humid zones and is also animportant cereal in many semi-arid areas. It is grownpredominantly in loose rotations with such crops asgroundnuts and sunflowers. and is often sparselyintercropped with beans, groundnuts, cowpeas orpumpkins. For semi-commercial crops such asmaize, seed for planting and fertiliser are the mainpurchased inputs. Table 1 summarises the maincharacteristics of smallholder maize-based croppingsystems in southern Africa.


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Table 1. Summary characteristics of main Smallholder Maize Production Systems in southern Africa*.

System characteristic

Maize croppingsTotal maize area (000 ha)Percentage of total areaMaize area perfarm (ha)Average yields tlhaPhysical environmefltAnnual rainfall (mm)Elevation m a.s.1.Major soil textures

Farming systems locationsMain geographicallocations

Other crops in additionto maize (% arable landoccupied)

IntercroppingPercentage of area

Main species

CattlePercentage farm output soldfor cashMain maize practicesMain varieties

Fertiliser usePercentage area fertilisedAverage application(kg/ha )Weed control

Ox cultivatorsSub-humid

1250312(1-10)1.5-2.5

700-12001000--1800sandy loamsandy (>70%)some loam andclay loam

central andnorth Zimbabwecentral and southernProv. ZambiaLesotho andSwazilandgroundnuts (20)finger millet (10)sunflower (5)colton (5), beans

5 (but most as sparsepumpkin and cowpeaintercrops)pumpkin and cow pea

Important50+

hybrids 80%+(e.g. R215,MM603)'local'maize80

80-120N, 10-20PMechanicaVhand-hoe(some delays, especially onlater plantings)

Semi-arid

110027I(0-4)0.25-0.75

300-700100-1200sandy loamloam (>90%)some clay

southern Zimbabwesouthern MozambiqueBotswana

sorghum (10-60)groundnuts (10)MilIets (10-30)

2

cowpea

Very important


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Achievements of FSAR in Southern AfricaSince the late 1970s and throughout the 1980s aFarming Systems Adaptive Research (FSAR)approach has been widely used by national agricultural research systems (NARS) in southern Africa todevelop and adapt agricultural technology suited tothe needs of smallholder farmers. FSAR has tendedto be commodity- and location-specific, and to focuson incremental change in production practices andinputs to ease their adoption by farmers. Theemphasis was on solving short-term production problems. This was done through informal diagnosticsurveys that identified and characterised on-farmproduction constraints, on-farm experiments thatmodified and tested technology under farmer circumstances, and the use of criteria for technologicalacceptability besides biological performance, such astiming of food availability, cooking and storagequality, breaking labour or draught power constraints, cropping system compatibility and risk (e.g.Collinson 1987; Low and Waddington 1991; Tripp1992).FSAR has had two core roles in the region:

to diagnose, identify and quantify productionproblems (and their related research opportunities)in key farm crop enterprises, and

to adapt or test technologies (inputs, equipment ortechniques) to address identified production problems and better suit the needs of smallholderfarmers (Collinson 1987; Low and Waddington1991; Waddington and Heisey 1991).The following paragraphs summarise CIMMYT'sperception on the achievements of FSAR in

southern Africa, concentrating on the two coreroles given above, with examples related to themanagement of soil fertility and climatic risk formaize. This summary draws heavily on the comprehensive reviews of Low and Waddington (1990,1991), Low et al. (1991), and proceedings of aregional network workshop on impacts of on-farmreseareh in eastern and southern Africa (Heisey andWaddington 1993).

Identification of production problemsObservers agree that FSAR programs in southernAfrica have been successful in diagnosing productionconstraints in maize and other crop enterprises and indeveloping relevant new research opportunities toovercome those constraints. Table 2 illustratesseveral examples related to soil fertility and riskmanagement.

Table 2. Examples of production constraints for maize related to soil fertility or climatic risk identified through adaptiveresearch on smallholder farms in southern Africa.Production problem and locationCurrent long-cycle hybrids perform poorly inareas with a short rainy season or under lateplantings. where late weeding is done or littlefertiliser used.Late planting is common and it greatly reducesyields. All current recommendations assumeearly planting.Draught power shortage is common in oxplough systems, leading to late planting.Basal and topdress fertiliser are often appliedlate. Little is known about fertiliser rates foropen pollinated maize, planted late on sandysoils.Late and inadequate weeding is common insmallholder maize.

Research opportunityDevelop earlier maturing hybrids and open pollinated varieties(commodity research).Test widely with farmers under their conditions and assessment criteriaDevelop maize adapted to late plantings (earlier maturity, tolerance to lowsoil fertility and to weeds) (commodity research) and test on-farm. Bringforward timing of topdress fertiliser.Adapt zero and reduced ox tillage systems on-fann.

Modify timings and rates of fertiliser to fit smallholder capability and forOPVs in semi-arid areas and late plantings.

Look at chemical and mechanical weed control to reduce labour anddraught power needed for weeding.

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Adaptation and testing of technologiesWhen the development, adaptation and testing ofimproved technologies for adoption by smallholderfarmers, mainly through participatory adaptive onfarm trials and demonstrations, are examined the current outcome is more mixed. There are many examples of FSAR successfully reducing inputs to levelssuitable for smallholders, adjusting management tofit smallholder circumstances and operational constraints and introducing methods that enable farmersto move toward known ideal practices (Low andWaddington 1991). Table 3 illustrates examplesrelated to soil fertility and reduced climatic riskfor maize.

In addition, FSAR has had some success in orientating commodity or disciplinary research to developtechnology appropriate for smallholders. For maize,most of the clearer examples involve orientation ofplant breeding efforts that include encouragement todevelop semi-flint hybrids in Malawi and offerearlier-maturing 'open pollinated varieties' (OPVs)and hybrids in Zambia. Indeed the greatest long-termimpact of FSAR in this region may not come throughits directly placing more appropriate technology inthe hands of smallholders, but by bringing togetherdifferent agricultural research and extensionapproaches and technical and socioeconomic staffto focus on their needs.

Compromised impact of FSARDespite these successes, it is widely appreciated thatthere has not been widespread adoption by farmersof technology outputs from FSAR. In a study of53 FSAR initiatives from Swaziland, Zambia andZimbabwe undertaken in 1991 (Low and Wadding ton1991; Low et aL 1991), only 15 initiatives had led toany adoption by farmers, of which just three technologies, all involving new varieties, were widelyadopted. Recent evidence suggests FSAR has hadsome further, but modest, impact on farmer practicesin this region (e.g. Chikura et al. 1993, Zimbabwe,and Warland et al. 1993, Swaziland).

Analysis suggests a variety of reasons why FSARimpact on farmer adoption and productivity has beenmoderate and slow. These range from simple overexpectations by donors and others of what FSARcould do, through technical shortcomings withinFSAR concerning over-reliance on 'fine tuning' ofexisting technology, with on-farm trials that wereoften inadequately designed, implemented, analysedand interpreted, to those of a more soeioeconomicand institutional nature. Included are overemphasison separate FSAR units divorced from the rest ofagricultural research, insufficient awareness of intrahousehold decision-making and gender issues infarming, ineffective links with extension services,and failure of FSAR to address deficiencies in input

Table 3. Examples and impacts of technologies to address soil fertility or climate risk for smallholder maize productionfrom on-farm adaptive research derived in southern Africa.Example of Technology Reasons for outcomeOutcome: Led to wide adoption of echnology by farmersShorter season open pollinated varieties and - provide food during hunger periodhybrids with semi-flint grain widely tested on- - suited to on-farm storage and processingfarm in Malawi and Zambia good performance with little fertiliserOutcome: Demonstrated advantage over current practice but little adoptionZero tillage with herbicide in Zambia Many and varied reasons for non-adoption include:On-row tillage with herbicide in Zimbabwe - little support by extensionHerbicide weed control on Swaziland - implement unavailableCombined weed and fertiliser management in - high cash cost to start usingZambia, Malawi and Zimbabwe - training neededOutcome: Confinned superiority offarmer practice over standard recommendationApplication of basal fertiliser at planting in yield gains were minor compared 10 farmer practice ofZimbabwe applying 1-2 weeks after planting- farmers reluctant to apply until seedlings emerge- labour shortage at planting time- slows down planting processOutcome: technology shown to be ineffective on-farmTIed ridges to stabilise yield on granitic sandy - little yield increase obtained in dry years but yield decreasedsoils in NR 3 and 4 in Zimbabwe in wet years due to waterlogging and low soil fertility in furrows

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supply and marketing and to respond by targetingagricultural policy makers with appropriate information (e.g. Low and Waddington 1991; Low et at.1991; Tripp 1992; Waddington 1993).Technical shortcomings in FSARThere is no doubt that technical shortcomings withinFSAR have constrained its impact. For example, inthe analysis of 53 FSAR initiatives from Swaziland,Zambia and Zimbabwe, Low, Waddington andShumba (1991) found that about 50% of the failuresof initiatives before adoption by farmers were due toimplementation deficiencies in FSAR, mostly relatedto on-farm trials.

Technical shortcomings within FSAR include: superficial characterisation of production problems and causes and difficulties in identifying the

bounds of target groups because of reliance onsingle-visit informal surveys of farmers in smallgeographical areas; lack of systematic planning procedures which,until recently, meant that the rationale for researchthrusts was often questionable; over-reliance on complex (multi-factor) on-farmexperiments with conventional designs from onstation research, leading to difficulties implementing trials and analysis and interpretation of

the results; difficulties in extrapolating research results fromlocation-specific on-farm trials to a wider farmingcommunity, meaning uncertainties of the value ofresearch results outside the immediate researchzone; and deployment of inexperienced staff and high staffturnover of staff (e.g. Waddington and Low 1988;Low and Waddington 1991; Shumba 1991;Waddington 1993).

For FSAR in more marginal, semi-arid environments, some inadequacies are more common andhave more serious implications. There is large microvariation within sites (leading to high coefficients ofvariations in on-farm trials) coupled with large variation in rainfall and soil types over sites (whichrequires testing at many sites and over several years),and often operational problems in working a longway fnJm home base (Chiduza and Nyamudeza1990). In some semi-arid areas many on-farmexperiments conducted over almost a decade haveled to little that can be recommended to farmers(Jeranyama 1992, for Chivi, Zimbabwe).

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It should be no great surprise that these inadequacies exist. As an holistic approach to research, FSARwas developed by social scientists, and in early yearsdrew on agronomic techniques then available. Onlyover the last few years have agronomists, biometricians and other technical scientists begun todevelop or modify techniques specifically for FSAR.Examples of recent improvements in FSAR methodsinclude multi-visit agronomic monitoring of crops infarmers' fields (Byerlee et al. 1991), and new experimental designs that better cope with micro-variation(Mead 1990).These technical shortcomings can be reduced bythe wider use of procedures that already exist withinFSAR, such as systematic planning procedures foron-farm experiments, use of simpler on-farm trialsthat can be analysed statistically across many sitesand seasons, newer experimental designs thataccount for variability, thorough agronomic and biological interpretation of results (including explanation of within-site treatment interaction in trials),economic analysis and assessments of risk, andcloser farmer participation in the research process(Waddington 1993).

Combining additional research approaches andtools with FSARIt seems impossible for the techniques described tobridge the gap between the current reality of FSARand the technology needs of smallholder farmers insouthern Africa. What then are the alternatives?

First, it seems unlikely that there are seriousalternative research frameworks or approaches thatcan do better than FSAR in providing smallholderfarmers with beneficial technology that they want touse. With FSAR now well established in NARS, amore constructive approach is to look at which additional research approaches and tools can be combined with FSAR to reduce the limitations of currentFSAR procedures.Role of crop improvementFor semi-arid areas, in particular, experience is thatfor most agronomic inputs and practices (such asridging systems, fertiliser) that imply certain recurrent costs but uncertain benefits, risk-averse smallholder farmers are reluctant to adopt them. On theother hand, improved seed is usually a cheap input(although the large development costs mayhave been absorbed at national level) and readilyadoptable.

Plant breeding for genotypes more efficient intheir use of limited chemical resources such as water


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and mineral nutrients will continue to reduce the riskassociated with cropping in marginal areas and opennew opportunities for agronomic research. As anexample, CIMMYT at its headquarters in Mexicoand in this region is developing maize with improvedtolerance to water deficits and with higher N fertiliser-use efficiency (Short and Edmeades 1991).Crop growth models and geographic infonnationsystemsComputer-based crop growth models and what havebecome known as geographic information systems(GIS) (e.g. Nix 1987) have great potential forincreasing the efficiency of adaptive agriculturalresearch in Africa. Among other things they help predict the effects of crop inputs and management undervariable minfall and soil fertility regimes (reducingthe need for empirical on-farm trials), and candelineate target agroecological areas or groups offarmers for which a particular technology is appropriate (e.g. Dent and Thornton 1988; Keating et al.1992).

Yet. while biological simulation models and GIShave many benefits for adaptive research, suchmodels have, as yet, several major limitations.Firstly, there is a lack of confidence in outputs fromcrop models in marginal areas of southern Africabecause their performance has yet to be tested forsuch areas and because sufficient minimum inputdata may not be available from such areas (Chiduzaand Nyamudeza. 1990). Secondly, current models areinsensitive to many sources of variation and complexity in smallholder cropping systems, such ascrop-livestock interactions, rotations, weed competition and intercropping (Dent and Thornton 1988;Thornton et al. 1990). Thirdly, while adequate GISdatabases are probably available for rainfall and tempemture, those on soils, soil fertility, and croppingsystems are not complete and too general, whilethose on biotic constraints such as weed pressurehave yet to be compiled.Even when versions of models with these sensitivities become available and when sufficient inputdata are amassed, the application of crop growthmodels and GIS should not be viewed as a new panacea. Evidence is already available to show thatwhen applied to smallholder farming in Africa, thethoughtful use of crop models may not lead to majormodification in farmer practice. The excellent workwith the CERESMaize model in semi-arid Kenya atKatumani (Keating et al. 1991; Keating et al. 1992)and the associated work on response farming

(Stewart 1991) led to greater understanding byresearchers of interactions between maize plant den-

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sity, moisture and N fertiliser, and to the demonstration of clear benefits from application of amounts ofN fertiliser conditional on rainfall events early in thecropping season (Wafula et al. 1992). Yet whileresearchers became more confident about promotingN fertiliser on maize in semi-arid eastern Kenya,such benefits were not easy for farmers to appreciate,and few farmers have so far adopted the practice.There is a major challenge for adaptive research andextension, (Wafula et al. 1992; Muhammad andParton 1992).While there is a long way to go in perfectingmodels for traditional African smallholder farmers,now is the time to integrate them into the mainstreamof agricultural research for smallholders in thisregion. This workshop has provided such anopportunity.

A 'sustainabil ity' perspectiveThe incorporation of a natural resource managementor sustainability perspective into agriculturalresearch presents new challenges and opportunitiesfor FSAR. The last five years or so have seenintense researcher and donor interest in the maintenance of biophysical resources such as soil water,mineral nutrient cycling and organic matter insmaLLholder farming systems and the often complexor composite technologies that may help, such asmultiple cropping, agroforestry and integrated pestmanagement.

Pure sustainability research has some characteristics not especially compatible with FSAR. Amongthese Posner and Gilbert (1991) identified longresearch lead times, scientific complexity, lack ofproven technologies and incompatibility with theproduction objectives of farmers. But a shared concern for the future (and some donor pressure) has ledto FSAR taking on some of the sustainabiLity perspective. For example, the most successful FSARprogram in southem Africa, Adaptive ResearchPlanning Team in Zambia, has for several years hadlong-term on-farm experiments that tackle soilfertility restoration or improvement (ARPT 1991).An integration of the sustain ability perspectiveshould be the way ahead, rather than separate 'sustainability researchers'. FSAR can provide sustainability researchers with expertise in working onsmallholder fanns, where most of the sustainabilityproblems exist, through experience in running onfarm trials. FSAR knowledge of farmer adoptionbehaviour also is vital in tailoring technology thatcombines long-term resource conservation with nearterm productivity increases, to encoumge adoption.


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ConclusionThe following papers cover in detail some of theseadditional research approaches and tools, especiallymodelling. They examine how, given their currentstate of development, such tools help research thattargets soil fertility and climatic constraints in smallholder dry land agricultural systems in southernAfrica. The challenge is to decide what theseapproaches can offer southern Africa, and how theycan be integrated with more established researchapproaches better to address the long-term technology needs of smallholders.

ReferencesAdaptive Research Planning Team 1991. ARPT in the1990s. Report of the ARPT Half-Yearly Meeting,Siavonga, 19-21 February 1991. Volume l. Record ofdiscussions, recommendations and future directions for

ARPT. Lusaka, Research Branch, Department ofAgriculture, 88p.Byerlee, D., Triomphe, B. and Sebillotte, M., 1991.Integrating agronomic and economic perspectives intothe diagnostic stage of on-farm research. ExperimentalAgriculture 27, 95-114.Collinson, M.P., 1987. Farming systems research: Procedures for technology transfer. Experimental Agriculture23, 365-386.Chiduza, C. and Nyamudeza, P., 1990. Implementation ofon-farm research experiments in marginal environment,:issues and challenges. Farming Systems Bulletin, easternand southern Africa 7, 13-19.Chikura, S., Mudhara, M., Mombeshora, B.G., Chibudu,c., and Jeranyama, P. 1993. Impact of on-farm researchon technology adoption by farmers: A case study inMangwende. In: Heisey, P. and Waddington, S., eds.,Impacts of On-Farm Research, Proceedings of a Networkshop on Impact


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Stewart, J.I. 1991. Principles and performance of responsefarming. In: Muchow, R.e. and Bellamy, l.A., eds.,Climatic Risk in Crop Production: Models and Management for the Semi-arid Tropics and Subtropics. Proceedings of the International Symposium on Climatic Risk inCrop Production: Models and Managemcnt for the Semiarid Tropics and Sub-tropics held in Brisbane, Australia,26 July 1990. Wallingford, England, CAB International,361-382.

Thornton, P.K., Dent, J.B. and Caldwell, R.M., 1990. Intercrop modelling: Applications and issues. Agriculture,Ecosystems and Environment 31,133-146.Tripp, R. 1992. Expectations and realities in on-farmresearch. Farming Systems Bulletin, eastern and southernAfrica 11, 1-13.Waddington, S.R. 1993. The future for on-farm crop experimentation in southern Africa. In: Heisey, P. and Wad-dington, S., eds., Impacts of On-Farm Research,Proceedings of a Networkshop on Impacts of On-FarmResearch in eastern and southern Africa. Lilongwe andHarare, CIMMYT, 160-167.Waddington. S. and Low, A., 1988. CIMMYT's on-farmresearch support program for eastern and southernAfrica. In: Gelaw, B., ed., Towards Self-sufficiency,

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Proceedings of the Second eastern, central and southernAfrica Regional Maize Workshop, Harare, Zimbabwe.Harare: CIMMYT, 160-167.Waddington, S.R. and Heisey, P.w., 1991. Adaptiveresearch achievements and failures, and its focus for thefuture in southern Africa. In ARPT in the 1990s, Report

of the 1991 ARPT half-yearly meeting, Siavonga, 1921February 1991. Volume 2,104-115.Wafula, RM., McCown, R.L. and Keating, RA. 1992.Prospects for improving maize productivity throughresponse farming. In: Probert, M.E., ed., A Search forSustainable Strategies for Sustainable Dryland Croppingin Semi-arid eastern Kenya. Proceedings of a symposiumheld in Nairobi, Kenya, 10-11 December 1990. ACIARProceedings No. 41, ACIAR Canberra. Australia, 101-

107.Warland. R.H., Dlamini. S.M., Hsieh, K.H., and Malaza,M.T. 1993. Swaziland cropping systems research andextension training project impact assessment study. In:Heisey, P. and Waddington, S., eds, Impacts of On-FarmResearch, Proceedings of a Networkshop on Impacts of

On-Farm Research in eastern and southern Africa.Lilongwe and Harare, CIMMYT, 365-382.


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Maize Water Use as Affected by Nitrogen FertilisationZ. Shamudzarira*

AbstractThe effects of nitrogen fertiliser on yield, water use and water use efficiency of maize wereinvestigated at two sites in Zimbabwe during the 1992-93 season (Makoholi and HRC,Marondera). Crops in 1991-92 at the same sites had failed due to drought.At both sites grain yield responses to N were large (increases up to 2 tlha) but total water use ateach site was not significantly changed. Thus water use efficiency improved from 1.6 10 4.9 andfrom 2.4 to 5.4 kg/halmm at the respective sites.The implications of these findings in terms of understanding nitrogen and water interactions.

and for modelling crop growth in semi-arid environments, are discussed.

DRYLAND farming systems revolve around the principle that water is the main limiting factor, and toincrease or maintain an adequate level of yield, onemust maximise the water use efficiency (WUE) forcrop production. While research work by the Department of Research and Specialist Services (DR&SS)in the semi-arid communal areas of Zimbabwe hascovered a wide range of topics over the years, theresults of most agronomic treatments can be interpreted in terms of their influence on the water andnitrogen balance. Plant populations, planting date,fertilisers, rotations, intercropping and soil surfacemanagement have all been studied in this context. Acommon problem that links most of the researchwork has been the difficulty of interpreting researchresults that vary greatly in response to seasonalvariations in rainfall amount and distribution.

Under dryland conditions, crops are subjected tounpredictable periods of high moisture stress betweenrains. I f in these periods of limited moisture fertiliserscan increase the nett assimilation rate or growthwithout exhausting water at a faster rate, then totalyield and WUE can be increased. If fertilisers accelerate the rates of both growth and water use (WU),the yield and WUE will depend on the total supply ofwater and the status of the crop when the moisturesupply becomes exhausted. Thus accelerated WU

*Department of Research and Specialist ServicesAgronomy Institute. Box 8100, Causeway, Harare

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through fertilisation can be disastrous for grain cropsif the moisture supply is exhausted and the rains donot come before the grains are filled.

Past reviews demonstrate that water requirementsof crops grown on poor soil may be reduced by halfto two-thirds by the addition of fertilisers (Viets1962). Some workers conclude that each plant mustattain a certain mass before grain production canbegin, that the critical mass is somewhat greater forplants grown in infertile soil, and that WUE is lessfor crops grown on infertile soil, resulting in a muchgreater water requirement to begin grain productionunder such conditions. The favourable effects offertilisers, when nutrients are deficient, on the massand distribution of roots have been reported and aregenerally well known. In general, fertilisationpromotes top growth faster than root growth, leadingto an increased top to root ratio. Some studies suggest that the improved WUE by fertilised crops wasaccomplished without noticeable increase in totalwater consumption. However, there are only a fewreports on the concurrent effects of N fertiliser ontotal water extraction and on vertical and horizontalchanges in the extraction patterns. Changes in depthof rooting or ramification of roots in the soil wouldbe of particular importance under conditions oflimited moisture supply where full exploitation ofsoil moisture would be of greatest significance.

In the current study, soil moisture measurementswere undertaken beginning in the 1991-92 seasonon field plots of maize. The basic objective of the


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experiment was to determine the amount and patternofwater use of the maize variety R201 fertilised withvarying rates of nitrogen under rainfed conditions onsandy soils.

Experimental ProceduresDuring the 1991-92 season one experiment wasestablished at Makoholi Experiment Station (seeTable 1). Two planting dates and six rates (0, 30, 60,90, 120 and 150 kg/ha) of nitrogen fertilisation treatments were planned. The first planting was done on17 December 1991, but emergence and plant establishment was so poor that the crop had to bereplanted on 22 January 1992. The planned secondplanting was done one week later. Nitrogen wasapplied in the form of ammonium nitrate. A basaldressing of 30 kg N/ha was applied to all plots exceptfor the controls. Due to the dry weather conditionsno N topdressing was applied. The crop was sprayedwith Thiodan to control blotch web.Table 1. Site characteristics.

Natural Mean annualSite region Soil type rainfall(mm)Makoholi IV 5G 614HRC Ha 7G.2 885SoillYpes: (see Thompson and Purves 1978)50: kaolinitic order (fersiallitic group), moderately shallow, greyish brown, coarse grained sands throughout

the profile fonned on granitic rocks.70.2: kaolinitic order (orthoferrallitic group), moderatelydeep reddish brown, coarse grained sandy loarns over

y e l 1 o w i ~ h red clay.In the 1992-93 season two experiments wereestablished, one at Makoholi and the other at theHorticultural Research Centre (HRC), Marondera(see Table 1). The three rates of nitrogen fertilisationwere 0, 30 and 60 kglha. Soil moisture determina

tions were done every two weeks at Makoholi, usinggravimetric sampling for the top 0-15 cm soil layersand using a neutron probe (CPN 503DR Hydroprobe) for the deeper soil layers down to a depth of90 cm. At HRC, soil moisture determinations to adepth of 45 cm were done gravimetrically. For allexperiments there were three replications.Water consumption by the crop was computedfrom the sum of water in the profile at the beginningof the season plus seasonal rainfall less profile moisture at harvest. Evaporation loss during the growing

season accounts for part of this total consumptionvalue. A correction was made allowing for around

16

10% runoff of the rainfall, to make moisture consumption values more realistic. Although strictlyempirical and no doubt an over- or under-estimate inmany cases, the error in this correction is presumedto be identical for all treatment levels.Results and Discussion

Cumulative water use, grain yields and water useefficiencyDuring the 1991-92 season there were no measurable responses to fertiliser application as the cropwas severely affected by the drought. The firstplanted crop received a total of only 82.9 mm rainfalland the second 35.9 mm. The second planting wentinto fairly moist soil compared to the first plantingbut below 15 cm depth there was negligible plantavailable moisture. The crop did not reach physiological maturity due to the prolonged drought. Laterinspections revealed that plant roots did not penetratebeyond 20 cm.

By contrast the 1992-93 season was fairly wet.The crops at Makoholi and HRC received 628.5 mmand 663 mm rainfall respectively. Levels of production were high at the experimental sites in responseto N fertilisation, which greatly improved water-useefficiency by the maize crop at both sites (seeTable 2).

Table 2. Influence of N fertilisation on total water use,grain yield and water use efficiency at MakohoJi and HRC.

Nitrogen levelkg nlhaTotal water use(mm)Grain yieldUhaWUEkglha/mm

SiteMakoholi HRC

o 30 60 o 30 60627.4 613.2 635.0 601.4 597.8 590.0

1.06 2.15 3.19 1.46 2.90 3.161.63 3.38 4.85 2.43 4.85 5.36

Cumulative water use and rainfall at Makoholiand at HRC during the 1992-93 season are shown inFigures lea) and J(b). Rainfall kept ahead of wateruse throughout the growth of the crop at Makoholi.Total water use from planting to maturity for thethree N treatments is shown in Table 2. The cropreceiving 30 kg N/ha used rather less water than thezero N crop (P=0.05) but produced a greater grainyield. Water use differences between the three fertiliser rates increased as the season progressed. At the


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highest rate of 60 kg N/ha, increasing amounts ofwater were used to reach each growth stage, becauseN had increased total plant growth and developed amore effective root system. For this treatment totalwater use was not significantly affected but grainyield increased to 2.13 t/ha. The water use efficiencyvalues were therefore greatly improved by N fertilisation. Stored soil water supplied 61.7, 47.8 and69.3 mm of water to the maize grown on the threerespective N treatments.

o

700 (b)

600

500

400EE300

200

100

00

64 121Days after planffng

43Days alterplanting

I90

Key:DO kg N/ha.30 kg Nlha 60 kg Nlhab. Rainfal

149 191

Key:o Okg NIha+ 30 kg'Nlha 60 kg Nlhah. Rainfall

I150

Figure 1. Cumulative water use and rainfall (a) Makoholi,1992-93, (b) HRC 1992-93.

17

At HRC, N fertilisation more than doubled thegrain yields and WUE values when compared to thecontrol crop. The improved WUE with fertilisationwas accomplished without any noticeable increase intotal crop water use. Compared to Makoholi, thecrop at HRC used, on average, less water but produced similar yields at the high N treatment. Thehigher total water use values at Makoholi areprobably related to the higher evaporative demand(mainly due to higher temperatures and lower humidities) at this site compared to HRC. Soil moisturewas progressively depleted by all crops to a depth of90 cm.

ConclusionsThe use of moderate amounts of nitrogen fertiliser in1992-93 more than doubled the water-use efficiencycompared to the control crop at both sites, increasesbeing almost in proportion to yield response tofertiliser. In other semi-arid regions of the world, abalanced nutrient supply has been found to enablethe crops to make more efficient use of the availablemoisture (Arnon 1975; Olson et al. 1964; Russell1973). It has been demonstrated that a nutrient deficient plant, even though it is not growing, or isgrowing slowly, is using water at about the same rateas a nutritionally balanced plant, yet will produce aconsiderably lower yield (Brown 1971). Workreviewed by Bolton (1981) indicates that differentlevels of soil moisture at seeding require differentlevels of applied nitrogen in order to balance themoisture and nitrogen supplies for maximum wateruse efficiency.

Crop yields from rain fed cropping systems inmost of the communal areas in the semi-arid zones ofZimbabwe are low and variable mainly due to thelow and erratic rainfall and the inherently poor soilfertility of the dominant granitic sands.There is great interest at the moment in easternand southern Africa in the use of crop models forassessing the potential of different management

strategies (including N fertiliser use) for sustainablecrop production (Keating et. al.l991). Basic researchOn the interactions of N use and crop water use canprovide a fundamental input for model developmentand validation. Work on calibrating and validatingthe CERES-Maize model (Version 2.1) for the localmaize varieties SR52 and R20l is currentlyunderway in the Department (DR&SS). Given thehigh variability of rainfall in the semi-arid areasof Zimbabwe and the large impact of moisturesupply on N-use efficiencies, simulation modelsthat describe the effects of weather on N supplyand demand can offer an invaluable tool for assessingN-fertiliser management strategies for these areas.


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ReferencesArnon, I. 1975. Physiological principles of dryland cropproduction. In: Gupta, U. S., cd., Physiological Aspects

of Dryland Farming. New Delhi, Oxford and IBH, 3-145.Bolton, F.E., 1981. Optimising the use of water andnitrogen through soil and crop management. Plant andSoil,58,231-247Brown, P. L. 1971. Water use and soil water depletion bydryland winter wheat as affected by nitrogen fertilisation.Agron. J., 63,43-46.Keating, B.A., Godwin, D.e., and Watiki, J.M. 199LOptimising nitrogen inputs in response to climatic risk.In: Muchow R.e. and Bellamy, I.A. ed. Climatic Risk in

18

Crop Production: Models and Management for the Semiarid Tropics and SUbtropics. C.A.B. International, Wallingford, U.K.0I80n, R. A., Thompson, e. A., Grabouski, P. H., Stukenholtz, D. D., Frank, K.D.,and Dreier, A.F. 1964. Waterrequirement of grain crops as modified by fertiliser use.Agron. J., 56, 427-432.Russell, E.W. 1973. Soil Conditions and Plant Growth.London, ELBS and Longman, 849 p.Thompson, I.G. and Purves, W.D. 1978. A guide to thesoils of Rhodesia. Rhodesian Agricultural JournalTechnical Handbook No. 3Viets, F.G., lr. 1962. Fertilisers and the efficient use ofwater. Adv. Agron., 14,223-264.


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The Potentials and Limitations of Agroforestry forImproving Livestock Production and Soil Fertility inSouthern AfricaB.H. Dzowela* and F. K wesigat

AbstractDrawing upon a wealth of research information available for the southern African subcontinent,the potential and limitations of agroforestry for improving animal production and soil fertility arediscussed. Agroforestry is reputed to incorporate essential components of sustainability and selfsufficiency into some agricultural systems. Evidence is given that agroforestry, by providing shade

in pastoral systems, thereby reduces heat stress in livestock and increases animal performance andoverall productivity. A wide range of agroforestry trees provide forage with high crude protein andIow fibre contents, making them a source of home-grown and cheaply available supplements forpoor quality roughage feedstuffs such as cereal crop residues. Evidence is presented that browsingon such trees improves feed intake, animal performance and overall utilisation efficiency of poorquality roughage. However, in some leguminous trees, the presence of tanniferous compoundscould cause depression of dry matter and nitrogen digestion in the rumen.Due to the inherent Iow soil fertility of major areas of the southern African subcontinent, and tothe rapidly increasing population pressures, systems of agricultural production that combine theuse of leguminous shrubs and trees to recycle nutrients of importance are discussed. Evidence isgiven that several agroforestry technologies, e.g. improved fallows, relay cropping, hedgerow intercropping and tree biomass transfer, can improve soil fertility and sustain crop yields.

A SYSTEMS approach to agricultural production insouthern Africa involves an integration of crop andlivestock production. Logically, this includes pastureand forage production on the lands which are marginal for cropping, and crop production on higherpotential land. Agroforestry is an activity that canenhance the production of both the crop and livestock subsystems. It can incorporate essential components of sustainability and self-sufficiency into thewhole agricultural system (Hazra and Rekib 199 I).This can be achieved by providing multiple productssuch as fuelwood and charcoal, timber for construction, food, medicines, tanstuffs, dyes, shade andshelter, by prevention of soil erosion and increase in

*Forage Agronomy, SADC-ICRAF Agroforestry Project,Zimbabwe, clo Department of Research and Specialist Services, PO Box 8 J08, Causeway, Harare, Zimbabwe.t Forestry, Zambia-ICRAF Agroforestry, clo Msekera Agricultural Research, Chipata, Eastern Province, Zambia.

19

soil fertility and by provision of forage for livestock(Sardinha and Sousa 1988). This review will attemptto highlight the potential and limitations of agroforestry in improving soil fertility and livestock production in the southern African subcontinent. To do thiseffectively, the experiences of the research thrust ofthe southern Africa Agroforestry Network will bedrawn upon, together with available informationfrom elsewhere in the sub humid and semi-aridtropics.

Livestock Production in the SouthernAfrican RegionSouthern Africa has broadly two types of livestockproduction. The first involves extensive use of land,i.e. low human and livestock density (de Leeuw andRey 1993). This type of system is common in thepastoral and agropastoral areas of the arid and semiarid zones where rainfall patterns preclude reliablecropping and limit the support capacity of land forboth people and livestock.


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The other system of livestock production, alsoextensive, exists in the higher potential areas alongwith mixed farming systems where overall land use isintensified, increasing population pressure. In thissystem the livestock subsector is used to increase theoverall output of land through exploitation of the synergism between cropping and livestock subsectorsthrough soil nutrient enhancement from livestock andimproved soil tillage through animal traction (deLeeuw and Rey 1993). However, while overall landuse becomes more intensified, livestock managementand feeding strategies remain extensive. Livestockcontinue to rely on natural pastures, plus crop residuesfor dry season feed; external feed inputs are appliedstrategically to increase productivity at certain times(Dzowela 1993). For instance, to improve the workoutput of traction (draught) oxen, supplementary feedis provided when demands for tillage and transport arehigh Le. early in the crop growing season and duringor after crop harvests (de Leeuw and Rey 1993).Benefits of trees for livestockShadeIn traditional livestock production systems, animalscrowd the shade of trees during hot sunny weatherand some trees in pastoral systems are browsed(Cameron et al. 1991). It is reported from work in the

Australian tropics that high temperatures can induceconeeption failure, abortion in pregnant ewes andreduced lamb birth weight (Roberts 1984).Young calves, and pregnant and lactating cows aremore susceptible to heat stress than other cattle, butall classes of animals grazing for a greater part of theday made greater weight gains in paddocks with

shade than in those without (Daly 1984). Shade significantly increased milk yield of dairy cows from17.2 to 19.2 kg/cow/day in the Australian tropics(Davidson et al. 1988).Leguminous trees for browseHistorically, the use of leguminous trees on thesouthern African sub-continent has been confined tothe lopping of native species for drought feeding oflivestock. Many species have value in this role; Pi1-iostigma thonningii, Combretum spp.. Brachystegiaspp. and a wide range of Acacia spp. are known inthese roles among herders (Sibanda and Ndlovu1992). Other species are shown in Table 1. No comprehensive chemical data is available for the majortree legumes used as fodder. A majority probablyhave high nutritive values, as suggested by data ononly a few of them (Table 2). These are among the200 main browse species listed by Le Houerou(1987) and Lamprey et aL (1980).

Table 1. Nitrogen-fixing tree and shrub legumes used for forage (by family, genera and species).Mimosoideae No. species Papilionoideae No. species Caesalpinoideae No. speciesAcaciaParaserianthesDesmodiumLeucaenaPithecellohiumPterocarpusProsopisSource: Brewbaker (l986)

12115124

CajanusChamaecytisusDesmanthusGliricidiaMedicagoPangamiaRohinia

ParkinsoniaCalliandraErythrinaSesbania

1I24

Table 2. Drymatter (glkg) and chemical composition (glkg DM) of Icoal browse (leaves and tender stem) at Matopos.Zimbabwe.Local Browse Species

Parameters Acacia karroo Acacia nilotica Securinega virosa Ziziphus mucronataDrymatter 568 513 382 484Nitrogen 19 25 34 26Crude protein 118 154 211 162Crude fibre 142 120 125 121Ether extract 24 41 35 23N-free extract 672 637 535 624Ash 44 47 94 70NDF 337 314 305 336ADF 235 225 208 216NDF Neutral detergent fibre ADF =Acid detergent fibre Source: Adapted from Dube and Ncube (1993)

20


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Among the exotic species, Leucaena leucocephalaand others such as Albizia spp., Calliandra caloth-yrsus, Gliricidia sepium, Cajanus cajan and Sesbaniasesban are increasingly proposed as suitable feedalternatives to herbaceous legumes, because the latterare unable to persist under heavy grazing (Blair et al.1990). Use of leguminous trees and shrubs is particularly appropriate where feed is carried to tethered animals, a common practice in the humid tropics.As most of the leguminous trees and shrubs usedin agroforestry have high crude protein values

(18-30%) and low fibre contents (9-30%) (Dzowelaet al. 1993), they are a good source of feed to supplement poor quality roughage, such as cereal crop residues; they improve feed intake, animal performanceand the overall utilisation efficiency of poor qualityfeedstuffs (Table 3).

However, limitations, exist in the use of the leguminous trees and shrubs fodder. The major constraint, in spite of their high nutritive value (Table 4),is the presence of such secondary compounds as condensed tannins and hydrolysabJe polyphenolics in

Table 3. Daily dry matter intake (DMI), dry matter digestibility (DMD), organic matter digestibility (OMD) and aciddetergent fibre digestibility (ADFD) of rations of maize husk supplemented with urea, Leucaena and/or Calliandra,and daily weight gain by goats.

Parameters Husk + Husk +urea Leucaena

Intake (gld)Maize husk 249a 149bLeucaena 182CalliandraLeucaena +CalliandraTotal DMI 249 331aDigestibility (%)DMD 47c 63aOMD 54c 65aADFD 43 52Average dailygain (g) 4.8d 28.5aDaily DMI(glkg"'S) 25 33FE (kgDMlkgweight gain) 52.ld 11.6aWhere: SE= error, = Feed efficiency;

FeedstuffsHusk +

Calliandra147b168

315b59b6lb5219.Oc3216.8c

Husk + Leucaena +Calliandra

149b

168317b60b62b55

22.6b32

14.2b

SE

0.9

1.21.20.70.70.1

Means followed by the same letter within the same row are not significantly different (P


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some trees. For instance, Dzowela et al. ( 1993)reported that of the seven major multipurpose treespecies currently showing potential for addressingquality fodder shortages during dry seasons in Zimbabwe, three had appreciable levels of condensedtannins and hydrolysable polyphenolics when leafmaterials were sampled 6 and 12 weeks after cuttingin May 1992. These are Calliandra calothyrsus (12.3g/kg DM), Acacia angustissima (10.3 g/kg DM), andFlemingia macrophylla syn. congesta (3.1 g/kg DM),but Sesbania macrantha had negligible amounts(Table 5). These compounds caused a depression indry matter and nitrogen degradation in the rumen.Correlation of polyphenolic compounds content withthe degradation coefficients of both dry matter and Nin the rumen was negative (correlation coefficient.-0.49). This was found to be significant (P


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Zambia, northern Malawi and the Shaba province ofZaire (Mathews et al. 1992; Stromgaard 1989) orforms of 'slash and burn' cultivation. However, pressure on land resulting from an increasing humanpopulation has resulted in longer cropping andshorter fallow periods (Kwapata 1984). Because soilsare not given time to regain their fertility, there is ageneral decline in crop yields, which has made thetraditional methods of restoring fertility eitherinappropriate or unsustainable.

Diagnostic and design surveys conducted in theregion by the International Centre for Research inAgroforestry (ICRAF) showed potential for agroforestry interventions which are likely to restorefertility more quickly (Huxley et al. 1986).Some Agroforestry Interventions

Improved rotational systems involving tree-cropfallowsNutrient pumping is cited as one of the potentialbenefits of trees in agroforestry systems; trees havedeep root systems which absorb nutrients from thesubsoil and deposit them in or on the surface soil viaabove and below ground biomass production, decomposition of prunings of leaves and branches, orindirectly through the deposition from manure ofbrowsing livestock (Nair 1984; Young 1989). Thisassumes that the translocation of nutrients to superficial soil horizons by trees can increase the amountof nutrients available to shallow-rooted vegetationand crops and improve overall productivity of theagricultural system.

Small-scale farmers who, until the presenteconomic depression, relied on subsidised inorganicfertilisers to produce maize, could make use of agroforestry technology via improved fallow systems

(Kwesiga and Coe 1993). Sesbania sesban-basedimproved fallows of 23 years duration have shownpotential in overcoming low soil fertility andincreasing crop yield with reduced or no inorganicfertiliser input. For instance, in sub humid Zambiawhere maize yield was about 1.5 t/ha without N fertiliser, Kwesiga and Coe (1993) reported that afterone, two and three years fallow with S. sesban theyield was increased to 3.5, 4.4 and 5.3 t/ha respectively without N fertiliser (Fig. 1). The responses inyield with increasing N fertiliser levels were reducedprogressively after zero to three year fallows,indicating that the effects of fallowing were largelyto improve soil N supply.8-

(J No FaDow1 Yr Fallow

" 2Y r Fallow.3 YrFallow

0+---------- . - - - - - - - - - , - - - - - - - - - - .okg Nlha 37 kg N/ha 74 kg N/ha 112 kg N/haFertiliser levels

Figure 1. Responses of maize grain yields to fertiliserafter different periods of Sesbania at Chipata, Zambia.Improvements in soil fertility are sometimes hardto demonstrate due to the complex nature of the processes involved. However, limited data are availablefrom the subcontinent. Table 6 shows some soil

Table 6. Comparison of soil chemical properties of the 0-5 cm depth of a sandy loam soil taken before planting a maizecrop after one. two and three-year S. sesban fallow and previously fertilised and non-fertilised maize plots at Chalimbana,Zambia.Exchangeable cations

Fallow period and Organic Total P K Na Ca Mg CECfertiliser treatments Maller N(%) (%) (ppm) (------"-meqllOO g soil ------)No fallow, no fertiliser 1.48 0'


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chemical properties on plots after one, two and threeyear S. sesban fallows compared with continuousmaize plots with or without 200 kg/ha diammoniumphosphate fertiliser (18-46-0 compound). Trendstowards increasing contents of Ca, CEC and to someextent organic matter occurred after one year tothree-year fallows even though the increases werenot statistically significant.In the densely populated areas of SouthernMalawi, where farmers cannot afford fallows, relaycropping of maize with fast-growing multipurposetree and shrub species such as S. sesban has produced good results. The relay cropping technology isa variant of improved fallows. Common multipurpose trees include Cajanus cajan and Sesbaniasesban, producing substantial maize yield gains(Maghembe, pers. comm.).Other candidate species for short duration fallows

may include species widely adapted to the subhumidzone of Southern Africa. These are Cajanus cajan,Flemingia macrophylla, Gliricidia sepium, Tephrosiavogellii and Acacia angustissima.Hedgerow intercropping (alley cropping)This technology refers to the planting of crops in thespaces between hedgerows of trees or woody shrubs(Rosecrance et al. 1992). Trees are pruned to minimise resource competition and maximise nutrientavailability to the crop. For nutrient recycling, theprunings are applied to the soil as green manure orincorporated as surface mulch (Kang et al. 1981). Inhumid environments, a wide range of crops can beplanted in the alleys. Between these. the fast-growingleguminous trees or shrubs provide prunings, stakesand nitrogen fixed from the atmosphere (Yamoah1988).

However, research results from the subhumid plateaux of southern Africa are showing that excessivecompetition for nutrients and moisture between thetree or shrub species and associated crops occurs inhedgerow intercropping systems. Also, climatic factors impose limitation, reducing leaf production oftrees and shrubs. Thus it is only in fertile soils ofhigh rainfall areas that the potential of hedgerowalley intercropping to improve crop yields has beendemonstrated (Kang et al. 1981; Akeyampong et al.1992). Even in these areas the benefits are obtainedonly at the cost of a high labour demand.BionmasstransferTwo forms of biomass transfer showing potential forsoil fertility improvement and hence better more sustainable crop yields exist in Zambia and Zimbabwe.

24

In Zambia, multipurpose trees are grown in pureor mixed stands outside the farm area allocated forcrop and livestock production. Tree leaf biomass iscut and carried from these stands to cropped land.Alternatively, it is cut and carried as fodder supplements for livestock feeding on a basic diet of poorquality roughage during dry seasons.In Zimbabwe, farmers have recognised the positive effects of woodland litter when applied to cropsand mixed with animal manure (Wilson 1989). Thereis a general belief among smallholder farmers that inyears of good rainfall, litter from Brachystegiallul-bernadia savanna woodland increases crop harvests.Farmers will apply woodland litter, usually to supplement kraal manure, to land cropped with a widerange of intercrop mixtures including maize (Nyathiand Campbell 1993).With the existing research background, it shouldbe possible to identify what role agroforestry technologies might have in improving livestock and cropproduction in the southern African region. Theplanting of trees should, apart from increasing cropand livestock production, provide other products andservices as well. The woody biomass remaining afterusing foliage and branches for fodder or manureprovides fuelwood, stakes and poles, therebyreducing the need for further deforestation ofremaining forest lands.

ConclnsionsThe potential and limitations for agroforestry havebeen reviewed with respect to animal and crop produetion in southern Africa, drawing upon resultsfrom current research. A wide range of leguminoustree and shrub species commonly recommendedfor agroforestry have potential use as fodder. Whengrown on-farm, they provide highly nutritious,high-protein and low-fibre supplements to poorquality roughage. Evidence exists that the readilydegradable materials have high potential as fodder.Only tanniferous materials could be constrainedin their utilisation by the presence of secondarycompounds.

Several trees and shrubs have high potential forimproving soil fertility and sustaining crop production. When integrated into farming systems forimproved fallows, relay cropping, hedgerow intercropping or biomass transfers, they could become auseful and profitable way of complementing expensive inorganic fertiliser use by resource-poor farmersin the Southern African sub-continent.


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ReferencesAkeyampong, E., Duguma, B., Heinman, A.M., Kamara,

e.S., Kiepe, P., Kwesiga, E, Ong, e.K., Otieno, H.J. andRao, M.R. 1992. A synthesis of ICRAF's research presented at the alley farming conference held at UTA,Ibadan, Nigeria September 1992.Blair, G., Catchpoole, D and Home, P. 1990. Forage treelegumes: Their management and contribution to the

nitrogen economy of wet and humid tropical environments. Advances in Agronomy 44, 27-54.Brewbaker, J.L. 1986. Guide to the Systematics of thegenus Leucaena (Mimosoideae: Leguminasae). Leu-caena Research Reports. 7 (2), 6-20.Cameron, D.M., Gutteridge, R.e. and Rance, SJ. 1991.Forest and fodder in multiple production systems I.Forest and fodder trees in multiple use systems in thetropics. Tropical Grasslands, 25,165-172.Daly, JJ. 1984. Cattle need shade. Queensland AgriculturalJournal, 110,21-24.Davidson, T.M., Silver, B.A., Lisle, A.T. and Orr, WoN.

1988. Revegetation one answer for salt degraded land.Rural Research 143, 1421.de Leeuw, P. N. and Rey, B. 1993. An analysis of distribution patterns of ruminant livestock in sub-Saharan Africa.In: Proceedings on African Savanna landuse and globalchange: Interactions of climate productivity and omissions, held on 25 June, 1993, Victoria Fails, Zimbabwe.Dube, 1.S. and Ncube, S. 1993. The potential of MatoposBrowse Species for livestock production. In: B.H.Dzowela and E.M. Shumba eds. Proceedings of theNational Seminar on Agroforestry in Zimbabwe, held on35 March 1992, Harare, Zimbabwe (in press).Dzowela, B.H. 1993. Advances in forage legumes: a Sub-

Sahara African Perspective. Proceedings InternationalGrassland Congress, PaImerston North, New Zealand(in press).Dzowela, B. H" Hove L.. Topp, 1.P. and Mafongoya. P.1993 Nutritional and anti -nutritional values and rumendegradability of drymatter and nitrogen of major Mptspecies with potential for Agroforestry in Zimbabwe.Agroforestry Systems (in press).Hazra, C.R. and Rekib, A. 1991. Forage productionscenario in the country national perspective in technology development and transfer. Agricultural situationin India 46.581-588.Huxley, P.A., Rocheleau, D.E. and Wood, P. 1986. Farmsystems and agroforestry research in north Zambia.Phase I Report Diagnosis of Landuse problems andresearch indications, ICRAF, Nairobi, Kenya.Kamara, C.S. and Chikasa, P. 1992. SADC-ICRAF Agmforestry Research Project, 1992 Annual Report, Chalimbana, Zambia, (ICRAF, Nairobi, Kenya). 36 p.Kang, B.T., WiIson. G.E. and Sipken L. 1981. Alley cropping maize (Zea mays) and Leucaena (Leucaena leuco-cephala Lam) in Southern Nigeria. Plant and Soil, 63,163-179.Kwapata, M.B. 1984. Shifting cultivation: Problems andsolutions in Malawi. In: FAO, The Future of Shifting

Cultivation in Africa and the Task of University, FAO,Rome, 77-85.

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Kwesiga, F. and Coe, R 1993. The effect of short rotationSesbania sesban fallows on maize yield. Forest ecologyand management (in press).Lamprey, H.E, Herlocker, D.J. and Field, C.R 1980.Report on the state of knowledge on browse in EastAfrica in 1980. In: H.N. Le Houerou cd. Browse inAfrica; The current state of knowledge. ILCA, AddisAbaba, Ethiopia 33-54.Le Houerou, H.N. 1987. Indigenous shrubs and trees in silvopastoral systems of Africa. In: H.A. Stepler and P.K.R.Naif eds. Agroforestrya decade of development, ICRAF,Nairobi, Kenya, 139-156.Phiri, D.M., Coulman, B., Steppler, H.A., Kamara, e.s. andK wesiga, F. 1992. The effect of browse supplementationon maize husk utilisation by g o a t ~ . Agroforestry Systems17, 153-158.Mathews, R.B., Lungu, S., Volk, 1., Holden, S.T. andSolberg, K. 1992. The potential of alley cropping inimprovement of cultivation systems in the high rainfallareas of Zambia 1. chitemene and Fundikila. AgroforestrySystems 17,219-240.Nair, P.K. 1984. Soil productivity aspects of Agroforestry.International Council of Research in Agroforestry(ICRAF), Science and Practice of Agroforestry No. I.85 p.Nyathi, P. and Campbell, B.M. 1993. The use of Miombolitter by small-scale farmers in Masvingo Province,Zimbabwe. In: Dzowela, B.H. and Shumba, E.M. eds.Proceedings of a National Seminar on Agroforestry inZimbabwe, held on 35 March 1992 (in press).Roberts, G. 1984. Plotting a better future for lambs Queens-land Agricultural Journal, 110, 25-26.Rosecrance, R.e., Brewbaker, J.L. and Fownes, 1.H. 1992.Alley cropping of maize with nine leguminous trees.Agroforestry Systems 17, 159-168.Sardinha. R.M. de A., Sousa, 1.N.P. de 1988. The role offorests ecosystems and increased availability of forage.Serie de Estudos Agronomicos, 15,27-33.Sibanda, H.M. and Ndlovu, L.R. 1992. The value of indigenous browseable tree species in livestock production insemi-arid communal grazing areas of Zimbabwe. In:Stares, lE.S., Said, A.N. and Kategile, l.A. edsProceedings of a Workshop on The complementarity offeed resources for animal production in Africa, held inGaborone, Botswana, 48 March, 1991 ILCA, AddisAbaba, Ethiopia 55-61.Stromgaard, P. 1989. Adaptive strategies in thc breakdown

of shifting cultivation: the case of the Mambwe, Lambaand Lala of Northern Zambia. Human Ecology 17,427-444.Wilson, K.B. 1989. Trees in fields in Southern Zimbabwe.Journal afSouthern African Studies, 15,369-383.Yamoah, e.E 1988. The potential of alley-cropping forhillside farming in Rwanda Appropriate TechnologyIntermediate Technology Publication. 15 (1), 28-30.Young, A. 1989. Agroforcstry for soil conservation. Science

and Practice ofAgroforestry No. 4, CAB International,Wallingford, UX 276 p.


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Computer Simulation Models as Management Toolsfor Sustainable use of Natural Resources inHighland-Lowland SystemsF. N. Gichuki* and H. P. Linigert

AbstractWise use and management of natural resources depends on a proper understanding of the interaction of the various components of the system and availability of aecurate and adequate information upon which to base management decisions. This paper highlights the efforts of LaikipiaResearch Project in developing management tools that can be used to (a) assess the effects of

present land use and management changes on soil and water resources and on primary production;(b) identify the potential for conservation and improved management techniques; and (c) assist inplanning for sustainable use of water, soil and vegetation resources.

NATURAL resources, particularly soil, water and vegetation resources, constitute some of the most important preconditions of man's existence and areimportant raw materials for his economic activities.Consequently, wise use and management of theseresourees is a prerequisite to sustainable production.Unfortunately, literature is replete with examples ofwidespread resource degradation, particularly in aridand semi-arid areas. Factors which contribute toresource degradation include: complexity of the production systems; high temporal and spatial variability in availabilityand quality of natural resources; scarcity of resources required for development,particularly capital and labour; competition for scarce resources among differentusers and associated conflicts; high production risk and, in some cases, lowreturn on investment;

*Department of Agricultural Engineering, University ofKenya, PO Box 30197, Nairobi, Kenyat Laikipia Research Project, PO Box 144, Nanguki, Kenya

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social and cultural constraints to adoption ofappropriate production technologies; laek of a proper understanding of the impacts ofvarious resource allocation and managementstrategies on socioeconomic status and environ

mental stability; and inappropriate policies.

This paper outlines some research approaches andachievements of the Laikipia Research Program(LRP), a joint venture of the University of Nairobiand University of Berne in developing analyticaltools for sustainable use and management of naturalresources in a highland-lowland system.

Description of the Highland-Lowland SystemNatural environmentThe study area consists of the Upper Ewaso Nyiroriver basin located to the west and north of MtKenya. This area is divided into four regions,namely: Mt Kenya humid slopes, Mt Kenya lowerslopes (transitional zone), semi-arid plateau (volcanicsoil) and semi-arid lowlands and hills (basementsoils) (Fig. 1). The study area has a dramatic variation in environmental characteristics, as shown inTable 1.


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SITE LEVEL STATIONSAgroccological Stations

LOCAL LEVEL STUDIES

Rumurutio

D Small catchments Nl . El etcREGIONAL LEVEL STUDIES Mt Kenya humid slopes (volcanic)Et Mt Kenya lower slopes: Transitional zoneD Plateau smi-arid (volcanic)D Mainly lowlands hills : mainly semi-arid (basement)

Figure 1. Water and soil resources management study area.Table 1. Environmental characteristics.Environmental variableClimateAltitudeAnnual rainfallSoilsVegetation

Range of characteristicsAfro-alpine, humid, semi-aridand arid5200-1000 m.above sea level1500-500 mmVertisols, Andosols, Luvisols,Lixisols, PhaeozemsMontane forest to acaciabushland

Socioeconomic environmentPopulation pressure in the study area began buildingup after J963, when former European farmers andranchers started sell ing their farms and ranches toAfrican land-buying companies. Kohler (1987)reported that the population of Laikipia district hasbeen growing at an annual rate of 7.3% due to immigration and natural increases. Population and landuse changes in the district are presented in Table 2.

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20Kilometres

Objectives of Laikipia research projectLaikipia Research Project (LRP) was established in1984 as an applied research project aimed at providing answers to questions raised by rural development projects. The overall goal of the ecology sectorof the project was to carry out applied research topromote sustainable utilisation of natural resources,with emphasis on soil, water and vegetation. Thescope has been expanded and the main objectives ofthe current program are:(I ) to develop management tools (computer programs) that can be used to evaluate:

the interaction of highland-lowland production systems; the effects of land use and managementchanges on soil, water and vegetationresources; and the effect of land-use and water-use patternson economic performance, environmentalquality and human welfare;


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Table 2. Population and land use changes.Parameter 1960Population* ('000)Human 20Cattle 250Sheep/goats 20Land use (% )Large-scale ranching 80Small-scale ranching 0Other (pastoralism, forestry) 20*Partly estimated. Source: Taiti s. 1992

(2) to apply management tools as a decision supportsystem for resource management at district and!or river basin level; and(3) to strengthen field research and modellingcapacities of the partner institutions and toimprove collaboration among them.

Approaches and AccomplishmentsEstablishing databanksEffective management of natural resource systemsrequires a clear definition of goals and objectives andan adequate and accurate database with informationon: the physical system in terms of natural characteristics, available resources and developmentpotential; resource use, allocation rules and associateddemands; organisational structures, policies, legal and socioeconomic aspects; and interractions and interrelationships of physical and

sociocconomic factors and their impacts onresource conservation, productivity and environmental quality.The importance of good data in resource management was realised at the inception of the project andan extensive data collection network established. Themain data sets collected on a regular basis includeclimatological, hydrological, soil, land use and vegetation, socioeconomic and experimental data.Although an assessment of the quality and quantity of data required had been done at the start of theprojeet, recent changes in approach have neeessitated

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1970 1980 199025 120 250125 180 250100 200 480

552520

a re-examination of the effectiveness of the data collection system, particularly for modelling purposes.The main procedures still unresolved are: determining the minimum data set required formodelling; dealing with missing data; satisfying model data requirements by regular datacollection; testing data for consistency and accuracy; use of remote sensing data such as NormalisedDigital Vegetation Index (NDVI), LANDSAT andMETEOSAT data in modelling; managing data to make it readily accessible todifferent computer modules and to reduce computer storage space and processing time; and using GIS in natural resources systems modelling.

Model development and validationAlthough the use of computers is spreading rapidlyin developing countries, few models have been dcveloped for African Mountain Systems and no modelling approach exists to assist the integrated planningof water, soil and vegetation resources, and the identification of productive and attractive conservationand management practices. This is due mainly to (1)the lack of adequate training and involvement ofAfrican scientists in model development, (2) the lackof adaptation of the models to the conditions indeveloping countries, (3) the lack of long-term datarecords to calibrate, verify and validate the modelcomponents, and (4) inadequate long-term supportfor model development and application in developingcountries.


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In developing countries, computer modelling willgain importance and will be needed in naturalresource management because it can be of great help,to: improve the understanding of the processes, andas an instrument to generate and test hypotheses; integrate different disciplines (climatology,hydrology, soil science, agronomy, crop/vegetation physiology, economics and sociology) andto bring researchers working in different areastogether; identify information gaps and to mmlmlse theneed for experimental baseline data; extrapolate from experimental data and elucidateeffects of climatic variability obtained over bothshort and long periods in the lowland-highlandregion; assess current and future risk areas of environmental degradation, and set up developmentstrategies; identify optimum resource management and al1o-cation options, to maximise primary productionand minimise environmental degradation; and investigate in a prospective way the consequences

of land-use change and the potential of resourceconservation and management techniques.Mt Kenya study region provides an unique opportunity to develop the model because of the followingfactors:

the wide variety of ecological zones, land-usetypes and dynamics within a short distance, andrespective problems of sustainable use of naturalresourees in this area, are typical of many Africanhighland-lowland systems; the Laikipia Research Program (LRP) has developed an extensive database (including GIS) andcurrently maintains a field station network relevantto the proposed modelling project; the proposed project fits into the core of the MtKenya Ecological Program (MKEP), which issupported by a wide range of organisations, andwill commence in 1994; and a model validation exercise has been proceedingsince 1992, the first modelling experience gainedwith the CERES model in collaboration withACIAR and CSIRO in Kenya (Keating et al.1992). Figures 2 and 3 show the validation of a

CERES-Maize model for Kalalu and MatanyaStations.

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The main areas of single process model development are studies of: weather generator effects, soil and water balance, land-use and settlement dynamics, vegetation and soil cover dynamics, erosion and sediment transport, streamftow, and water demand and allocation.

12000

10000


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identify eXlstmg models and their simplifyingassumptions, undertake sensitivity analysis of model parametersand input data, collect field data (where none exists) relevant formodelling the process, validate model with existing data sets, evaluate each model, select the model with the closest fit, modify the model to incorporate local conditions,and calibrate and revalidate the modeL

Modelling will be applied to three scales (seeFig. 4).Site scale (Jam! or paddock scale)This scale level covers small areas (plots) with uniform land use and natural characteristics 1-5 hectares. The basic idea is to calibrate and developindividual simulation modules and to link them to acentral data-base or data exchange. The individualmodules such as water balance (including runoff,deep percolation, crop water use, soil and groundwater changes), erosion and crop growth and yieldsmust be able to simulate different resource management practices. Simulation will be performed in timesteps of one day or less. Data sets for calibrating thevarious model modules are already available, theresults of more than five years of Kenyan-Swisscooperative field research.Small catchment scaleRunoff and sediment transport will be modelled onan event base while the water balance will be computed daily. The model on this level needs to bedeveloped, whereby established models will beadapted and combined with routines for datamanagement and exchange. The link between themodels on the site and the small catchment level willbe of special interest. The GIS component is important in order to link the different scales. Model calibration will be based on data from eight smallcatchments ranging in size from 1 to 5 km2 in forested, agricultural and range areas in the highlandand lowland zones.River basin scaleModelling of runoff and sediment transport will bedone on a sub-basin scale (one hundred to severalthousand km2) based on data collected from 15 subbasins using 30 runoff stations as a reference within

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the Upper Ewaso Nyiro Basin. The modelling will bebased on the principles developed on the small catch- .ment scale and the simplification or generalisation ofthe processes occurring there.Model Applications and Relevance toDevelopment

After the models are validated, they will be used byresearehers, as tools in communication, learning andmanagement

Figure 4. The three scales of modelling.

Research toolThe models, particularly single process models, willbe used to improve our understanding of the processes, and will also allow the use of informationobtained at several locations over a short period torecord changes in natural resources over larger areas,longer periods of time, and in relationship to variousscenarios.


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CATCHMENTIRIVER BASIN SIMULATOR

SOCIOECONOMIC ENVIRONMENTALMODULES MODULESDATABASE/EXCHANGE

1. Rainfall Rainfall2. Soli. EvapotranspirationWeather generation3,LanduselSoil Climatic changecover WATER BALANCEI ' ; ; ' ~ ~ ~ 4. Catchment I n f i l t r a t i O ~Targets boundaries Runoff/runonManagement 5. Landforms Groundwater -Pollcles (re)discharge. Pricing 6, Climate

EROSION:SEDIMENT7, Settlement TRANSPORT",o\t1er VEGETATIONICQVERDYNAMICS

........ Interface between modules and central database/exchange

Figure 5. System modelling approach.

Learning and communication toolsThe development and application of the models willcatalyse the communication and collaboration amongthe different scientists involved and enhance the integrated understanding of processes in highland-lowland systems among scientists, administrators andimplementors.Management toolThe models will be used to assess different scenariosand provide answers to management questionssuch as: the impact of changes in land use and management on productivity and sustainability of water,soil and vegetation resources; allocation of water resources among highland andlowland users; minimum farm size for smallholder farms in semiarid areas and the impacts of subdivision; impacts of climatic change on water and sedimentyield and on primary production;

economic and environmental consequences ofdifferent scenarios; and the policies most appropriate for good management.

ConclusionsThe necessary foundation for effective modelling hasbeen laid in the form of established relevant databases, building human resources with a capacity formodelling, acquiring existing models, and solicitingfor collaborators in our modelling exercises, themajor partners being LRP, ACIAR-CSIRO-DPI, theUniversity of Berne Group for Development andEnvironment, and the Rockefeller Foundation.

Additional funds are still needed to enable Australian modellers to take a more active role in providing backstop assistance in further modeldevelopment and/or adoption. We would also like toimprove collaboration with eastern and southernAfrican scientists to enable us to adapt and applymodels to a wider scope.

ReferencesIkonyn, S., Keating, BA., Liniger, H.P., Larkings, A.G.1993. Using a crop model to explore the benefits ofmulch in the Laikipia highlands. Paper presented for the3rd International Workshop of the African MountainAssociation (AMA), 4-14 March 1993, Nairobi, Kenya.Keating, B.A., Wafula, B M. and Watiki, J M., 1991. Development of a modelling capability for maize in semi-arideastern Kenya. In: Probert, M.E., cd., A Search for Strategics for Sustainable Dryland Cropping in Semi-arideastern Kenya, Proceedings of a symposium held inNairobi, Kenya, 10-11 December 1990. ACIAR Proceedings No. 41. ACIAR, Canberra, Australia, 26-33.Kohler, T. 1987. Land use in transition: Aspects and problems of African small-scale farming in a new environment: The example of Laikipia District, Kenya.Geographica Bernensia, African Studies Series, V1. A5.Berne.Liniger, H.P., 1992. Water and soil resource conservationand utilisation on the northwest side of Mt Kenya.Mountain Research and Development, VoL 12, No. 4,1992,363-373.Taili, S., 1992. GIUB-GFEU Workshop and Excursionhandout, Laikipia Research Program, 2-7 March 1992,Thomas, M.K., 1993. Development of a streamflow modelfor rural catchment in Kenya. MSc thesis, ComellUniversity, Ithaca, N.Y., U.S.A,

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Strategies for Soil-water Management for Dryland CropProduction in Semi-arid TanzaniaN. Hatibu*, H.F. Mahoo*, E.M. Senkondo*, T.E. Simalenga*,B. Kayombo* and D.A.N. Ussiri*

Overview

AbstractThe vagaries of weather, especially rainfall, are considered by most farmers to be the mostimportant limitation to agricultural production in the semi-arid areas of Tanzania. Therefore, aboveall else, the capture and efficient uti lisation of rainfall is considered to be the most important management option. This paper explains the research work started in 1991-92 season in the semi-aridareas of Tanzania to identify management interventions fo

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