Effect of nitrate application and shade treatment on the nitrogen fixation and yield of soybean plant

Abstract

Abstract Under sterilized-controlled conditions, soybean plant was grown with nitrate (N), Rhizobium inoculation (R), or nitrate and Rhizobium inoculation (N+R); under natural light or continuous shade conditions. Plant growth, respiration of root system, and yield were investigated in relation to nitrogen fixation. Nonnodulated plants (N) accumulated larger amount of dry matter as compared to (N+R) plants, and the opposite was found true at pod filling stage when the plants were exposed to natural light. R-plants were found to be the lowest in the accumulation of dry matter and the earliest in senescence. Nodule size and not nodule number, proved to be a good indicator for the nitrogen fixing activity. Nitrate suppressed both the size and specific activity of nodules. Specific respiratory activity of nodules was estimated to be up to three times as that of roots. Regarding seed yield, R-plants were the lowest and N-plants were the highest. (N+R) plants were the highest in the pod number per plant, while R-plants were almost the lowest in yield components. It was suggested that adequate supply of combined nitrogen in addition to nodule fixed nitrogen was necessary to get high yield.