The effect of soil moisture on light interception and the conversion coefficient for three landraces of bambara groundnut (Vigna subterranea)

Three landraces of bambara groundnut (Vigna subterranea (L.) Verdc.) were g rown as crop stands in controlled environment glasshouses at the Tropical C rops Research Unit, University of Nottingham, in 1995. Two soil moisture tr eatments were imposed: irrigated to 90 % field capacity each week and irrig ated to 60 % field capacity until establishment (27 days after sowing) with no further irrigation. Seasonal mean fractional interception varied betwee n 0.20-0.37 for the droughted treatments and 0.62-0.74 for the irrigated tr eatments, resulting in cumulative intercepted radiation of 228-350 MJ/m(2) and 662-794 MJ/m(2), respectively. The maximum total dry matter (DM) produc ed was 5.8 t/ha at final harvest (145 days after sowing) with a pod yield o f 2.7 t/ha. Under moisture stress there was little difference in DM product ion between landraces, with the highest total DM of 1.1 t/ha and a pod yiel d of 0.05 t/ha, representing a harvest index of 0.05 compared with an avera ge of 0.46 for the irrigated treatments. The conversion coefficient was red uced from 1.00 under irrigation to 0.51 g DM/MJ radiation intercepted by so il moisture stress. Two of the landraces showed adaptive mechanisms to avoi d drought; these are discussed in relation to maximizing seasonal radiation interception.