Supplemental Nitrogen Fertilizer to Soybeans : I. Effect of Side-dressing at early ripening stage on yield, yield components and protein content of seeds

Abstract

Effect of nitrogen side-dressing at 10 days after flowering on yield, yield components and protein content of seeds was examined using 12 varieties and ammonium sulfate. 1. Mean yield among 12 varieties supplemented with 120 kg nitrogen per ha increased by 6.7 percent or 250 kg per ha (Table 1). The most affected variety was Chippewa (13.2%) and the least was Waseshiroge (0.1%) (Fig. 1). 2. As to the early or medium varieties, yield increase was mainly due to the increase of 100 seeds weight. As to the late varieties, on the other hand, it was mainly due to the increase of pod number (Fig. 1). 3. Nitrogen or protein content of seeds increased by 3.3 percent on the average of 12 varieties supplemented with 120 kg nitrogen per ha. Protein yield per unit land area increased also by 10.3 percent (Table 2). 4. Effect on yield of supplemental nitrogen was the largest on the least fertile plots, and vice versa. On the least fertile plots all of the yield components, pod number, number of seeds per pod and 100 seeds weight increased. On the most fertile plots, on the other hand, pod number decreased, which negated the increase of 100 seeds weight, hence the least yield increase (Fig. 3). 5. Taking into account of the increase of total revenue due to the increase of yield and input cost for ammonium sulfate and labour for its dressing, the most reasonable amount of supplemental nitrogen was supposed to be around 100 kg per ha. In this case the increase of net revenue was about 35, 000 yen per ha.