Optimizing nitrogen supply promotes biomass, physiological characteristics and yield components of soybean (Glycine max L. Merr.)

Avoidable or inappropriate nitrogen (N) fertilizer rates harmfully affect the yield production and ecological value. Therefore, the aims of this study were to optimize the rate and timings of N fertilizer to maximize yield components and photosynthetic parameter of soybean. This field experiment consists of five fertilizer N rates: 0, 75, 150, 225 and 300 kg N ha(−1) arranged in main plots and four N fertilization timings: V(5) (trifoliate leaf), R(2) (full flowering stage) and R(4) (full poding stage), and R(6) (full seeding stage) growth stages organized as subplots. Results revealed that 225 kg N ha(−1) significantly enhanced grain yield components, total chlorophyll (Chl), photosynthetic rate (P(N)), and total dry biomass and N accumulation by 20%, 16%, 28%, 7% and 12% at R(4) stage of soybean. However, stomatal conductance (g(s)), leaf area index (LAI), intercellular CO(2) concentration (Ci) and transpiration rate (E) were increased by 12%, 88%, 10%, 18% at R(6) stage under 225 kg N ha(−1). Grain yield was significantly associated with photosynthetic characteristics of soybean. In conclusion, the amount of nitrogen 225 kg ha(−1) at R(4) and R(6) stages effectively promoted the yield components and photosynthetic characteristics of soybean.