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Project R6283 Forest/Agriculture Interface (including Hillsides) Production System

Project completed in 1998

Sustainable Nutrient Cycling in Crop/Livestock Systems

Experimental and simulationmodelling techniques were used toexamine the implications ofchanges in nitrogen dynamics inanimals on the behaviour ofnitrogen in soils to which theirexcreta have been added, and onthe resultant growth of plants onthese soils.

BackgroundThe importance of nitrogen cycling inthe mixed farming systems of sub-Saharan Africa and other developingcountries has received only patchyattention from researchers anddevelopment planners. Minimisingnutrient losses through promotingeffective recycling of nitrogen (andother nutrients) is a key issue inmaintaining the sustainability of manysmallholder mixed farming systems.The pivotal role played by livestock inregulating nutrient flows has generallybeen ignored in experimentation andcrop modelling even though livestockare a tightly integrated part of thesystem. Smallholder farmers lackreliable support in planning their farm

Natural Resources InstituteUniversity of GreenwichChatham, UKP.J. Thorne, D. Thomas

Imperial College at WyeUniversity of LondonAshford, UKG. Cadisch, K.E. Giller, R. Delve

International Livestock ResearchInstitute (ILRI)Nairobi, KenyaJ.C. Tanner, W. Thorpe

Kenya Agricultural ResearchInstitute (KARI)Nairobi, KenyaS. Kimani

management practices to respond tochanging environmental, demographicand market conditions.

Research highlightsAnimal metabolism studies in Kenyaindicated that considerable variationcould be induced in manure quality bydietary manipulation. Changes innitrogen supplementation radicallyaltered the total amounts of nitrogenexcreted and how it is distributedbetween faeces and urine. This maybe expected to have implications forthe timing of nitrogen release after themanure has been incorporated intothe soil.

The dynamics of nitrogen mineralisa-tion in soil samples may be affectedby the origin of the manure, i.e. by theanimal’s diet. Manure produced fromdiets of barley straw supplementedwith Calliandra calothyrsus andMacrotyloma axillare had similarnitrogen mineralisation patterns. Netcumulative nitrogen release occurredby week 16 after incorporation,following a lag phase of 12 weekswhen the nitrogen was immobilised.There is evidence that nitrogen isimmobilised for at least 12 weeksfollowing applications of all manure

types, suggesting that application atplanting – a common local practice –may not always be most effective inpromoting crop growth.

The potential significance of theseobservations was confirmed by potseedling growth studies in which thehighest dry matter (DM) assimilationwas observed after 12 weeks intreatments where no manure hadbeen added. Reductions in DM yieldsassociated with the addition of manureproduced from the different treatmentdiets ranged from 6 to 27 per cent incomparison with the un-manuredcontrol. This is consistent with theobserved pattern of immobilisation ofsoil nitrogen.

An on-farm study on the effects ofmanure applications in the tea, coffeeand semi-arid zones to the east ofNairobi has started to examinewhether the project’s experimentalfindings are borne out in the farmer’sfield. Findings from one seasonindicated that the nitrogen immobilisa-tion observed in experiments, typifiedby the lag in growth responses, maywell be occurring in the field.

Modelling activities in parallel with

Intensive returns of excreted nutrients from tethered livestock. Nutrients in the feed(maize stover, on the ground to the right) are transferred via the cow to the manure,ready for collection/composting.

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these experi-mental studiesled to thedevelopment ofthe simulationmodel ANORAC(Allocation ofNitrogen inOrganic Re-sources forAnimals andCrops). Amongother things,ANORAC allowsthe conse-quences ofdifferent strategies for using organicmatter (e.g. as litters, green manures,feeds) to be evaluated.

UptakeLivestock feed management decisionshave the potential to influence nitro-gen flows in soils according to whichmanures of different origin areincorporated. Livestock are clearly anintegral and dynamic part of the mixedfarming system. ANORAC is able toevaluate the trade-offs relating tonitrogen management that arise whendecisions on the use of organic mattermust be made. The lag phase be-tween the application of manure to thesoil and the net release of nitrogenhas considerable significance forplanning organic manure applicationsin practice. Dietary factors need to betaken into account. Application ofmanure at planting may not always bethe most effective in promoting cropgrowth.

LinkagesWork initiated by the project continuedin the bilateral context with a PhDstudent carrying out soil fertility-related work in East Africa under the

This Project Summary is an output from the Livestock Production Programme funded bythe United Kingdom’s Department for International Development (DFID) for the benefit ofdeveloping countries. The views expressed are not necessarily those of DFID.

aegis of a joint TSBF/CIAT (TropicalSoil Biology and Fertility Laboratory/Centro Internacional de AgriculturaTropical) initiative.

The ANORAC model was distributedto scientists in International Agricul-tural Research Centres (IARCs) andNational Agricultural ResearchOrganisations (NARs). The modeluses simple input variables, that canbe readily available to scientists innational research programmes indeveloping countries, to evaluate theeffects of different feeding strategieson manure quality and the release ofnitrogen from incorporated manure.

Relevance to sustainablelivelihoodsThe ultimate sustainability of highlyintegrated farming systems such asthe study system in Kenya is oftenprecariously balanced. Inappropriateinterventions in single system compo-nents (livestock, soil, crop) canexpress themselves elsewhere in thesystem with adverse effects on bothproductivity and sustainability. ‘Im-provements’ in feed utilisation bylivestock can reduce nitrogen flows to

other system components which mayresult, in the longer term, in thedepletion of soil nitrogen capital. Thewider appreciation of this message bythe stakeholders in intensifyingsystems is likely to have an importantimpact on preserving systemsustainability.

Selected project publications• Cadish, G., de Oliveira, O.C.,Cantarutti, R., Carvalho, E. andUrquiaga, S. (1997) The role of legumequality on soil carbon dynamics insavanna ecosystems. pp. 47–70. In:Carbon and Nutrient Dynamics inNatural and Agricultural TropicalEcosystems. Bergstrom, L. andKirchman, H. (Eds.). CAB International,Wallingford, UK.

• Delve, R.J., Tanner, J.C., Kimani,S.K., Giller, K.E., Cadisch, G. andThorne, P.J. (1998) The effects of feednitrogen and polyphenol levels on thefate of ingested nitrogen in steers andtheir implications for nitrogen cycling inmixed farming systems. p. 87. In:BSAS/KARI Proceedings of InternationalConference on Food, Lands and Liveli-hoods: Setting Research Agendas forAnimal Science, Kenya AgriculturalResearch Institute, Nairobi, 27–30 January1998. British Society of Animal Science,Edinburgh, UK.

• Thorne, P.J. (1999) Developingintegrated models for application incrop/livestock systems. pp. 105–121.In: Proceedings of a Workshop on Eco-regional Research at ILRI, AddisAbaba, 5–8 October 1998. Thornton,P.K. and Odero, A.N. (Eds.). Interna-tional Livestock Research Institute,Addis Ababa, Ethiopia.

The ANORAC model developed by the project can be used to evaluate theconsequences of different organic matter management decisions.

For further information on the Programme contact:The Programme Manager

Livestock Production ProgrammeNR International

Park House, Bradbourne LaneAylesford, Kent ME20 6SN

<w.richards@nrint.co.uk or lpp@nrint.co.ukwww.nrinternational.co.uk