The above-ground competition between common bean (Phaseolus vulgaris L.) and barnyardgrass (Echinochloa crus-galli L.) affected by nitrogen application

Competition for shared above-ground (e.g. light) and below-ground (e.g. water and nutrients) resources among neighbouring plants is one of the main processes that affect cropping systems. This study aimed to evaluate the effects of weed shading on growth and yield production of bean plants when grown in weedy condition without below-ground competition. The experiments were organized as a split plot design with three replications. The main plots consisted of the nitrogen application rates including of 0, 70, 140 and 280kgNha(-1) and the sub plots consisted of barnyardgrass densities including 0 (D-0), 2 (D-2) and 20 (D-20) plants m(-2). The N application rates were 0 (N-0), 25 (N-25), 50 (N-50), 100% (N-100) and 200% (N-200) of the recommended N rate on the basis of seed yield goal. Biomass of common bean decreased by 30% for N-0, 41% for N-50, 35% for N-100 and 38% for N-200, as weed pressure increased from D-0 to D-20.. Mean reduction in 100-seed weight, seed number and seed yield caused by high weed pressure was 11, 20 and 41% compared with weed free, respectively. The weed biomass and N uptake increased by 66 and 159% as the nitrogen dose increased from N-0 to N-200. The highest biomass and N uptake was obtained from N-200 treatment. We conclude that agronomically optimum N rates for seed yield was obtained at 140kgNha(-1) within the range of N fertilization rates used across all weed pressure levels.