Effects of nitrogen nutrition levels on N accumulation and yield of soyabean.

Labeled 15N ammonium sulfate was used as nitrogen source to study the effects of nitrogen nutrition levels on soybean(cultivar Dongnong 47) N-accumulation and yields using the sand culture.The results show that the crop N-accumulation and yields are increased earlier and decreased later as the exogenous-N levels are gradually increased,and the crop N-accumulation and yield are the highest when the nitrogen concentration is 50 mg/L.Applying N fertilizer during the R4 and R5 periods could increase the crop N-accumulation and yield significantly.Soybean growth and development needs "startup-N",and the best effect of the "startup-N" on the soybean N-accumulation is until the V3 period.Proportion of soybean absorption of exogenous-N is increased when enhancing the application level of the exogenous-N,while proportion of nodulation-N is decreased.The accumulation of the exogenous-N and accumulation of nodulation-N are increased earlier, and decreased later.The accumulation of exogenous-N is the main source when the nitrogen concentration is 100 mg/L,while the accumulation of nodulation-N is the main source when the nitrogen concentration is 50 mg/L.The accumulation of exogenous-N and accumulation of nodulation-N are increased apparently when continuously using "startup-N" until the V3 period.The exogenous-N absorption is increased apparently when high level of exogenous-N is applied during the R4 and R5 periods.