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Using legume trees to improve livestock fodder and soil fertility

Published: 20 May 2019

Agroforestry with legume trees is a way to improve livestock fodder quality and soil fertility in the tropics. In her new thesis, Marguerite Mukangango has evaluated biomass production by three legume tree species in Southern Rwanda and determined their effects on fodder quality. In addition, she has assessed the quality of the resulting manure as fertiliser and its effect on a maize crop yield and the fertility status of the soil.

The world’s population is expected to increase to 9.7 billion by 2050 with more rapid growth in East and North Africa. According to FAO, to meet food needs the agricultural production in sub-Saharan Africa and Asia needs to more than double by 2050. In the rest of the world the projected increase needed would be about one-third of the current level.

– Soil fertility depletion is the main cause of a widespread decline in land productivity in sub-Saharan Africa. High population densities that cause high pressure on land, soil erosion, nutrient leaching, removal of crop residues and continuous cultivation are some of the factors responsible for this soil fertility depletion, says Marguerite Mukangango.

Sigrun Dahlin and Naramabuye F.X. investigate plants that have been cut to provide feed for livestock. Photo: Marguerite Mukangango
Marguerite Mukangango in the field with her supervisor Naramabuye FX during her field work in Rwanda.

Choosing the right trees for agroforestry

Agroforestry is a land use management system in which trees or shrubs are grown around or among crops or pastureland. This combination of agriculture and forestry can increase biodiversity and reduce erosion. Agroforestry using legume trees, that can be cropped to produce shoots that livestock can eat, is a way to improve livestock fodder quality and soil fertility.

– Agroforestry has many positive aspects but can also reduce crop yields in some instances, due to competition for resources among trees and crops. Therefore, it is important to choose the right tree species and have an appropriate tree management regime to achieve sustainable production in the system, says Marguerite.

Three legume species tested on acidic soil with low nutrient content

In her thesis, Marguerite has evaluated the biomass production of the legume trees Acacia angustissima, Leucaena pallida and Mimosa scabrella. The trees were grown on an acidic soil with low nutrient content in Southern Rwanda.

– I wanted to determine the effects of the trees on feed quality. I looked at the manure´s fertiliser quality and effect on a maize crop, and the fertility status of the soil, says Marguerite.

Robust species for agroforestry was found

Higher biomass production was generally found at lower cutting height. Acacia angustissima had the highest biomass production, whereas M. scabrella was sensitive to repeated harvests. Mixing legume leaves with Rhodes grass improved the protein and mineral content. It also made the grass easier to digest for the animals.

Manure application increased soil pH, soil nutrient content, soil organic carbon, soil cation exchange capacity and water-holding capacity at maize planting stations (planting holes or root zone). The maize quality and yield improved with a manure micro-dosing method where small amounts of manure are applied at planting stations.

– We can now recommend A. angustissima and L. pallida as they are robust species for use in agroforestry systems similar to ours. They are also recommended to improve low-quality forage. Manure micro-dosing is a promising practice for soil fertility replenishment in crop production by smallholder farmers with limited income and access to manure to meet fertilizer recommendation rates, concludes Marguerite.

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