Relay‐Intercropping of Sunnhemp and Cowpea into a Smallholder Maize System in Zimbabwe

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Abstract
The rising real prices of purchased inputs is driving smallholder maize (Zea mays L.) production towards lower levels of inorganic fertilizer. Legume intercrops are a source of plant N that can be produced locally and offer a practical complement to inorganic fertilizers. Field experiments conducted on a loamy sand (Typic Kandiustalf) soil evaluated the impact of relay‐intercropping two legume crops, cowpea (Vigna unguiculata L.) and sunnhemp (Crotolaria juncea L.) into smallholder maize in Zimbabwe. The objectives were to quantify: (i) biomass and N yield of intercropped legumes, (ii) the impact of the legumes on companion maize yield and N uptake, and (iii) the response of a subsequent maize crop to legumes. Dry matter yield ranged from 0.6 to 4.6 Mg ha−1 for cowpea and 0.9 to 2.9 Mg ha−1 for sunnhemp, over two years. At the most, cowpea and sunnhemp produced 154 and 82 kg N ha−1, respectively. Companion maize grain yields were not reduced when the legumes were relay‐intercropped into maize fertilized at 0 to 60 kg N ha−1. However, maize yields were reduced 18 to 31% when maize + legume intercrops were fertilized at 120 kg N ha−1. In the subsequent year, maize grain yields were increased by 8 to 27% following maize + legume when no fertilizer N was applied, compared with maize following maize. Legumes reduced fertilizer needs of a subsequent maize crop by 36 kg N ha−1. Intercropped annual legumes and small amounts of inorganic fertilizer offers a strategy to meet the N needs on smallholder farms.

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