Soybean (Glycine max (L.) Merr.) is one of the most important food and cash crops in China and a key protein source for the farmers in northern China. Previous experiments in both the field and greenhouse have shown that N2 fixation alone cannot meet the N requirement for maximizing soybean yield, and that N top-dressing at the flowering stage was more efficient than N top-dressing at the vegetative stages. However, the effect of N fertilizer application at other reproductive stages of soybean is unknown. Thus, a field experiment was conducted to study the effects of N applications at various reproductive stages on growth, N2 fixation and yield of three soybean genotypes. The results showed that starter N at 25 kg ha¿1 resulted in minimum yield, total N accumulation and total amount of N2 fixed in all three genotypes. N top-dressing at 50 kg ha¿1 at either the V2 or R1 stages, significantly increased N accumulation, yield and total amount of N2 fixed in all three genotypes. However, N top-dressing at the same rate at either the R3 or R5 stage did not show this positive effect in any of the three genotypes. Thus, the best timing for N top-dressing during reproduction is at the flowering stage, which increased seed yield by 21% for Wuyin 9, 27% for You 91-19, and 26% for Jufeng, respectively, compared to the treatment without N top-dressing.
Gan, Y. B., Stulen, I., Kuiper, P. J. C., & van Keulen, H. (2003). Effect of N fertilizer top-dressing at various reproductive stages on growth, N2 fixation and yield of three soybean (Glycine max (L.) Merr.) genotypes. Field Crops Research, 80(2), 147-155. https://doi.org/10.1016/S0378-4290(02)00171-5