Abstract
The contributions of fertilizer N and Rhizobium japonicum inoculation were determined on paddy fields at two locations which differed in soybean cropping history. Levels of inoculation were none, on seed only, and on seed and in the furrow. N fertilizer levels were zero, 20 or 25, and 80 or 50 kg N ha-1. Nodule number, nodule weight and N yields were determined. Fertilizer increased N yield at both locations, but inoculation increased nodulation and N uptake (by 60% above those from uninoculated plants) only where soybean had not been cultivated previously. Where it was cultivated previously, nodulation in uninoculated treatments was abundant, demonstrating that flooded rice cultivation did not reduce the R. japonicum population to low levels. Although N fertilizer and inoculation increased N yields of soybean grown after paddy harvest, less than 80 kg N ha-1 was taken up by the early pod-filling stage. This N yield is insufficient for high grain yields
