Maize and Legume Interactions in a Multi-Species Relay Cropping System in Southern Africa.

A major challenge to the adoption of maize (Zea mays L.)-legume rotations among small landholders in Southern Africa is a strong reliance on maize as a staple grain. Intercropping dual purpose legumes with maize may be a viable alternative to rotations for small landholders in the region. The objective of this study was to determine the optimal time to plant lablab (Lablab purpureus L.) into a maize monoculture and maize-cowpea (Vigna unguiculata L.) mixture to maximize maize and cowpea grain yields and legume aboveground biomass production. A two-year field study was conducted in Limpopo Province, South Africa during the 2013-14 and 2014-15 rainy seasons. Results from the 2013-14 season are presented. A split-plot design was used with maize monocultures and maize-cowpea mixtures as whole plots, while subplots consisted of lablab planted 0, 2, 4, and 8 weeks after planting whole plots. Maize was planted in basins supplemented with cow manure (236 g basin-1) and sidedressed with 12-9-12 (5.4 g basin-1). Maize and cowpea grain yields were not affected by lablab planting time and averaged 1630 kg ha-1 and 687 kg ha-1 across treatments, respectively. Cowpea intercropped with maize and lablab produced 2.23-3.23 Mg ha-1 of biomass (dry matter) by 4 months after planting (MAP). Lablab planted simultaneously with maize, either with or without cowpea, accumulated little biomass while maize and cowpea were actively growing; however, between 4 and 6 MAP, lablab biomass increased by 225% (maize-lablab) and 300% (maize-cowpea-lablab). Lablab growth during this period led to soil temperatures that were up to 4°C lower than maize monocultures. Preliminary results suggest that maize grain yield is not affected by legume intercropping, while cowpea intercropped with maize can provide a supplemental food source. Lablab showed potential for substantial biomass accumulation after maize and cowpea senescence, providing ground cover into the dry season.