Bean growth and yield response to irrigation, nitrogen fertiliser,

Abstract

Beans (Phaseolus vulgaris var Mwezi Moja) were grown in the field under two irrigation levels (irrigated and rainfed), two nitrogen levels (no fertiliser and 100 kg N ha-1) and two planting densities (22 and 44 plants m-2) at Sonning (UK) and Kabete (Kenya). The crop duration in the three experiments was 114 days in Sonning, 95 days in K1 and 73 days in K2. Irrigation increased total dry matter early in the season at Sonning but had no effect at Kabete experiments because of high rainfall in K1 and ‘ineffective' irrigation in the drier K2 where most of the water was lost through evaporation. Total above ground dry matter (TDM) production at Sonning was higher than at Kabete in the wet season (K1 experiment) despite very similar weather conditions. Total dry matter and seed yields were lowest in the dry season Kabete experiment (K2). Nitrogen increased TDM at Sonning and K1 experiments but not in K2. High planting density increased TDM in all the experiments, and bean planting density response was most sensitive early in the growing season when plant competition for resources like light, water and nitrogen did not limit growth. Average seed yields were highest at Sonning (332 g m-2) and least in the K2 experiment (130 g m-2). Irrigation did not affect seed yield in any of the experiments. Application of N increase seed yield at Sonning and K1 but not in K2 experiment. High planting density increased seed yield at Sonning. Irrigation did not have a significant effect on Photosynthetically Active Radiation (PAR) interception in the three experiments. The dominant treatment effects on PAR interception were the nitrogen-density interaction at Sonning and K1. Neither N fertiliser nor planting density had a significant effect on PAR interception in K2. The leaf area index (LAI) and its duration mainly influenced radiation interception, and was the largest contributor to differences between treatments and experiments in radiation interception and hence TDM production and ultimately seed yields. The differences in seed yield among the three experiments was explained by differences in the number of seeds per plant and seed weight while the seed filling duration accounted for the differences in final hundred weight. Nitrogen fertiliser increased TDM production if water was not limiting while high planting density increased TDM if water and N were not limiting. A key to bean production improvement is establishment of a substantial LAI that is durable through the reproductive phase.