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INTEGRATED AGRICULTURAL SYSTEMS

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

^a Dep. of Crop and Soil Sciences, Michigan State Univ., East Lansing, MI 48824 USA
^b IFS Program, W.K. Kellogg Foundation, One Michigan Ave. East, Battle Creek, MI 49017 USA
^c CIMMYT-Zimbabwe, P.O. Box MP 163, Mt. Pleasant, Harare, Zimbabwe

rharwood{at}pilot.msu.edu

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.

Abbreviations: PAR, photosynthetically active radiation • RCBD, randomized complete block design • FRV, fertilizer replacement value

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