Organic matter technologies for integrated nutrient management in smallholder cropping systems of southern Africa

Snapp, S S and Mafongoya, P L and Waddington, S (1998) Organic matter technologies for integrated nutrient management in smallholder cropping systems of southern Africa. Agriculture, Ecosystems and Environment, 71 (1-3). pp. 185-200. ISSN 0167-8809

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One of the biggest challenges in the tropics is to develop organic matter technologies which are adopted by the farmers. Technologies must be effective within farmer resource constraints, increase food production, reduce risk and enhance the soil fertility. Results from on-farm participatory research were used to quantify the effects of agronomic practices on soil resources. Agricultural productivity is primarily nitrogen (N) limited throughout Malawi, and sub-humid Zimbabwe. Tightening economic constraints faced by farmers in the region have reduced inorganic fertilizer inputs and necessitate increased reliance on biologically-fixed N and N cycling. Three components of organic matter technology were evaluated: (1) the effects of residue quality; (2) the role of deep rooting systems; and (3) tradeoffs between legumes grown for grain versus soil regeneration. Perennial systems investigated include improved fallows, intercropping, and biomass transfer. Annual systems include intercrops and rotations of cereals with legumes. The most promising non-food legumes were Tephrosia and Sesbania. Interestingly, high quality residues of perennial legumes were most effective at supplying N in the short to medium term, whereas low quality residues immobilised N. Low quality residues were problematic for smallholder farmers who need immediately available N. Challenges to adoption of perennial system technologies include establishment costs, resource competition and delayed benefits. Farmer adoption of annual grain legumes is promoted by the simultaneous production of food; however, those species which have a high N harvest index add little to no net N to the soil. Species that combine some grain yield with high root and leaf biomass, thus a low N harvest offer a useful compromise of meeting farmer food security concerns and improving soil fertility. Promising genotypes include Arachis, Cajanus, Dolichos and Mucuna spp. On-farm N budgets indicate that legumes with high quality residues and deep root systems are effective ways at improving nutrient cycling. Areas of future research priority for smallholder farms in southern Africa were identified, including technologies which combine inorganic and organic fertilizer and improve legume growth and establishment on degraded soils

Item Type: Article
Uncontrolled Keywords: Soil fertility; Residue quality; Grain legumes; Agroforestry
Subjects: Others > Food and Nutrition
Others > Fertilizer Applications
Depositing User: Ms K Syamalamba
Date Deposited: 28 May 2014 05:52
Last Modified: 28 May 2014 05:52
Official URL:
Acknowledgement: UNSPECIFIED
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