Impact of soil moisture on nodulation, biological nitrogen fixation and yields of selected tropical legumes

Field studies were conducted over the dry seasons of two consecutive years to determine the impact of moisture stress on root-nodule number, patterns of N assimilation and grain or biomass yields of ten tropical food, greenmanure, and fodder legumes, using 15N. The plots were either rain-fed, which was insufficient for crop growth or irrigated to maintain soil moisture at 75 to 90% of field capacity. All measured parameters were affected by moisture deficiency; however, nodulation was the least influenced. Species prone to adverse effects from drought were affected to a greater extent than cowpea and pigeon pea, which are tolerant of or resistant to drought. The impact of water stress was greater on biological N2 than on yields. The drought-susceptible species extracted a greater proportion of N from soil than from fertilizer. (author)