Study on fertilizer-N absorption and distribution of soybean ［Glycine max (L).］during the seed-filling period

This experiment was conducted by using15N labeling method with staged design to study nitrogen assimilation and absorption by the soybean plant during the seed-filling period, especially the distribution of fertilizer N among different organs of soybean. The results show that total nitrogen accumulation during the five labeling experiments (0-25 d after beginning of seed-filling) plays an important role in nitrogen accumulation in soybean plant, which is about 291.4 mg/plant, occupies 48.9% to the total nitrogen accumulation in the labeling experiment Ⅴ. The nitrogen accumulation is decreased sharply during the seed filling period, which is from 109.5 mg/plant in the labeling experiment Ⅰ(0-5 d after beginning of seed-filling) to 19.6 mg/plant in the labeling experiment Ⅴ. Nodulation-N is the main source of the plan assimilated N, which is about 67.4%, and nodulations-N accumulation is decreased from 67.5 mg/plant in the labeling experiment Ⅰ to 10.8 mg/plant in the labeling experiment Ⅴ. Fertilizer-N accumulation is also decreased with the seed-filling process, from 42.0 mg/plant in the labeling experiment Ⅰ to 8.8 mg/plant in the labeling experiment Ⅴ. Fertilizer-N accumulation in different organs of soybean in different labeling experiments exhibits the same orders: seeds＞leaves＞stems＞roots＞pod walls, and the proportion of seed N accumulation from the fertilizer is increased from 27.9% to 85.0% during the labeling period.