Relay intercropping and mineral fertilizer effects on biomass production, maize productivity and weed dynamics in contrasting soils under conservation agriculture

Abstract

SUMMARYCash-constrained farmers who cannot afford herbicides and mineral fertilizers may incorporate green manure cover crops (GMCCs) as relay crops to aid in management of weeds and nitrogen in maize systems under conservation agriculture in cases where rotations are a challenge. An experiment was conducted at two sites with contrasting soil types, University of Zimbabwe farm (clay) and Domboshawa Training Centre (sandy) to investigate the effects of maize/velvet bean intercropping at 8 weeks after planting maize (WAPM), applying different fertilizer rates and exploring their interactive effects on weed composition, maize productivity and biomass production [total maize non-cob biomass (stover) plus GMCC biomass]. The performance of the system depended largely on the amount of rainfall received within and across the seasons, sites and their interaction; also on the amount of fertilizer applied. Generally, biomass yields attained by velvet bean [Mucuna pruriensL. (DC.)] were lower than reported previously. Maize grain yield and weed diversity were higher in treatments with higher fertilizer rates, reaching up to 5·1 t/ha and 1·39, respectively. Generally, the highest weed diversity and highest maize grain yield values were observed in maize/velvet bean combinations and higher fertilizer rates (i.e. 0·27 and 4·8 t/ha, respectively) in the sandy soil. Higher fertilizer rates resulted in greater maize stover yield and this contributed greatly to the biomass productivity of the system in the sandy soil in the 2012/13 season, while the high biomass productivity observed in velvet bean in the clay site in the final season contributed significantly to productivity. Maize productivity was not affected by velvet bean introduced at 8 WAPM in any of the seasons. The present study showed that relay cropping velvet bean as late as 8 WAPM and onwards has potential to increase biomass production without compromising maize yields. However, planting it as late as 8 WAPM results in reduced productivity due to reduced moisture availability.