Optimum phosphorus application rate for maintaining high yield and soil phosphorus fertility under winter wheat–summer maize rotation in Shanxi Province

Objectives The goal of determining the optimal phosphorus fertilizer application rate was to ensure a high and consistent crop output while maintaining long-term soil phosphorus fertility.

Methods From 2016 to 2019, a field experiment with winter wheat–summer maize rotation system was conducted in the south of Shanxi Province. P₂O₅ at 0, 120, 180, 240, 300, and 360 kg/hm² per year were the tested P fertilizer application rates. The P fertilizer was evenly divided into two portions in wheat and maize seasons. At harvest, crop P uptake, yield, and soil available P content were measured.

Results P absorption, yield, crop profit, and soil available P content were low when no P was applied (P0). Soil available P content decreased from 18.5 mg/kg in 2016 to 4.0 mg/kg in 2019, with an annual loss of 4.8 mg/kg. From 2017 to 2019, the P application increased yield by 23.9% and profit by 20.4% on average compared to P0. The linear plateau model fit the relationships between P uptake, yield, profit, and phosphorus application rate. The determined optimum P₂O₅ rate was 193 kg/hm², with partial factor productivity, agronomic efficiency, and phosphorus fertilizer utilization efficiency of 115.9 kg/kg, 21.9 kg/kg, and 25.1%, respectively. Distinct rates of P treatment resulted in different variations in soil available P content. On average, the P120 and P180 treatments reduced soil available P by 3.0 mg/kg and 1.3 mg/kg, respectively, whereas the P240, P300, and P360 treatments increased by 1.5 mg/kg, 4.0 mg/kg, and 4.2 mg/kg, respectively. The P₂O₅ rate that maintained the initial soil P level (Olsen-P 18.5 mg/kg) was P₂O₅ at 192 kg/hm², 194 kg/hm², and 197 kg/hm² based on regression of P application rate and soil available P content.

Conclusions Under the winter wheat and summer maize rotation system in southern Shanxi Province, the optimum yearly P₂O₅ rate for high crop production and profit, relatively high fertilizer efficiency, and preserving initial soil available P content is 193 kg/hm².