Abstract
Declining crops yield in the smallholder farmers cropping systems of sub-Saharan African (SSA) present the need to develop more sustainable production systems. Depletion of essential plant nutrients from the soils have been cited as the main contributing factors due to continues cultivation of cereal crops without application of organic/ inorganic fertilizers. Of all the plant nutrients, reports showed that nitrogen is among the most limiting plant nutrient as it plays crucial roles in the plant growth and physiological processes. The most efficient way of adding nitrogen to the soils is through inorganic amendments. However, this is an expensive method and creates bottleneck to smallholder farmers in most countries of sub-Saharan Africa. Legumes are potential sources of plant nutrients that complement/supplement inorganic fertilizers for cereal crops because of their ability to fix biological nitrogen (N) when included to the cropping systems. By fixing atmospheric N2, legumes offer the most effective way of increasing the productivity of poor soils either in monoculture, intercropping, crop rotations, or mixed cropping systems. This review paper discuses the role of cereal legume intercropping systems on soil fertility improvement, its impact on weeds, pests, diseases and water use efficiency, the biological nitrogen fixation, the amounts of N transferred to associated cereal crops, nutrients uptake and partition, legume biomass decomposition and mineralization, grain yields, land equivalent ratio and economic benefits.
Highlights
In traditional agriculture, arable land is left fallow for some years to allow soil to acquire self-rejuvenation, but due to increased population pressure, fallow periods are shorter and are not sufficient to restore the soil nutrient pools sufficient to support economic crop yields (TASDS, 2001)
Maize is the most cereal crop produced by about 82% of all Tanzanian farmers (NBS, 2007)
Cereal-legume cropping systems control insects and diseases by provision of barrier that prevent the spread between the host and parasite. This has been reported by Seran and Brintha (2010) on bud worm and corn borer infestation in sole maize being greater than in maize intercropped with soybean
Summary
Arable land is left fallow for some years to allow soil to acquire self-rejuvenation, but due to increased population pressure, fallow periods are shorter and are not sufficient to restore the soil nutrient pools sufficient to support economic crop yields (TASDS, 2001). The Soil fertility depletion is a widespread limitation to yield improvement in maize based intercropping systems throughout Eastern and Southern Africa (Mekuria & Waddington, 2002; Keston et al, 2013). It is widely considered as a major factor contributing to low productivity and non-sustainability of existing production systems and a major source of low returns to other inputs and management committed to smallholder farmers (Sanchez & Jama, 2002; Mekuria & Waddington, 2002). Studies on N2 fixation in the complex cereal-legume cropping systems are few and there is a need to identify and develop cereal-legumes intercropping systems that would influence N2 fixation in agricultural systems and complement fertilizer-N use as a sustainable means for soil fertility improvement and crops yields
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