Assessment of the optimum fertilizer rates and planting density for soybean production in China

Fertilization rate and planting density are important factors affecting crop yield. A large number of soybean [Glycine max (L.) Merr] field experimental data (1998-2017) were collected through different database sources to evaluate the optimum fertilizer rate and planting density for high yield of spring and summer soybean in China. The yield of spring and summer soybean gradually increased over year, with their average yields were 2610 and 2724 kg ha-1, respectively. Based on the fitted quadratic curve, the optimal rate of nitrogen (N), phosphorus (P), and potassium (K) fertilizers for high yield of summer soybean was 96 kg N ha-1, 80 kg P2O5 ha-1, and 126 kg K2O ha-1, and the corresponding yields were 3038, 2801 and 2305 kg ha-1, respectively. The optimal rate of N, P and K fertilizers for spring soybean was 71 kg N ha-1, 108 kg P2O5 ha-1 and 74 kg K2O ha-1, and the corresponding yields were 2932, 2834 and 2678 kg ha-1, respectively. The optimum density was 27x104 and 34x104 plants ha-1 under high yield for summer and spring soybean, respectively. Stepwise regression analysis showed that the P fertilizer had the greatest influence on the spring soybean yield followed by K fertilizer and planting density. For summer soybean, population density had the major effect on yield followed by P fertilizer. Overall, the P fertilization and planting density should be payed attention to increase soybean yield in different regions of China.