Effects of phosphorus reduction measures on winter wheat yield and phosphorus uptake and utilization in Weibei dryland

Objectives Continuous phosphorus (P) application might be a reason for the low wheat P use efficiency and soil P availability in the upland winter wheat production area of Weibei, the Loess Plateau. So, we studied the effects of P fertilizer reduction and the fertilizer application methods on wheat yield and P use efficiency.

Methods A three-year winter wheat field trial was carried out in the rainfed area of the Loess Plateau (Yongshou County, Shaanxi Province). The experiment included no P fertilizer control (CK), farmers’ practice (FP, P₂O₅ 120 kg/hm² by broadcasting), merely P fertilizer reduction (RP, P₂O₅ 70 kg/hm² by broadcasting), P reduction combined with banding application (BF), and with ammonium sulfate replacing urea (SA). Wheat plants were sampled at jointing, heading, and maturity stage for measurement of root morphology, shoot and grain weight and P content. At the same stages, soil (0−20 cm) samples were collected to determine the soil water, pH, and available P content. The water and P fertilizer use efficiency, and soil P budgets were calculated.

Results Compared with CK, P fertilization increased grain yield and P uptake by 640.8 kg/hm² and 3.95 kg/hm², equal to an increase rate of 11.4% and 28.2% on average of 3 years, however, P application rate and method did not cause significant differences. FP and RP treatments increased the root total length and surface areas. Compared with the FP treatment, the RP, BF, and SA treatments significantly increased P fertilizer use efficiency and decreased P surplus. Of these three treatments, the RP treatment significantly increased the partial factor productivity of P by 70.2%, the agronomic efficiency by 72.6% and P recovery efficiency by 4.4 percentage points, reduced apparent P surplus by 12.7 kg/hm² (62.5%) and soil accumulated P surplus by 63.3 kg/hm² and thus resulted in a decrease of P surplus rate by 21.8 percentage points. Under the same rate of P fertilizer application, compared with the RP treatment, the SA treatment significantly reduced soil pH at wheat jointing and heading stages (0.07 unit), and P surplus rate by 1.4 percentage points.

Conclusions In the Weibei dryland areas of Loess Plateau, reducing the P fertilizer (P₂O₅) application rate from 120 to 70 kg/hm² can maintain winter wheat yield and soil P supply, improve P use efficiency, and reduce P surplus. On the basis of reduced P fertilizer input (RP), the input of ammonium sulfate instead of urea (SA) and banding application of P fertilizer (BF) did not improve wheat yield, P and water use efficiency, however, the SA treatment could effectively adjust the soil pH in wheat jointing and heading stages and decrease soil P surplus rate at maturing stage. Therefore, the method of reduced P fertilizer input combined with ammonium sulfate fertilizer could be used as an optimal P management regime to achieve high wheat yield and efficient utilization of P resources in the Weibei dryland areas.