Threshhold of soil available P and the response of wheat yield and grain N, P, and K concentrations to test-integrated fertilizer application in the northern wheat production region of China

  Objectives  We studied the changes in wheat grain yield and NPK concentration due to test-integrated P application at different soil available P levels. The study aims to provide information on the efficient and green production of wheat.

  Methods  Wheat field experiments were conducted in 49 locations in China’s northern wheat production region from 2018 to 2020. The treatments were farmers’ fertilizer application rate (FF), recommended P fertilizer application rate (RF), and using test-integrated fertilizer application, and no P application (RF-P). The P₂O₅ rate in RF was reduced by 60 kg/hm², corresponding to 46% lower than the rate in FF. The grain yield, yield components, grain N, P, and K concentration, and P uptake and utilization by wheat were analyzed under different soil available P levels. Soil samples were collected at harvest stage of wheat to measure available nitrogen, phosphorus and potassium content in soil

  Results  The minimum grain yield (5155 kg/hm²) was recorded when soil available P was lower than 15 mg/kg, and the maximum (7217 kg/hm²) was observed at 25–30 mg/kg P in the soil. Higher soil available P did not increase grain yield sustainability. The observed reduction in grain yield was due to a significant decline in spike number and 1000-grain weight. Across the soil available P levels: <15, 15–20, 20–25, 25–30, and >30 mg/kg, the wheat yield in RF was similar to FF. However, P fertilizer uptake efficiency (1.03 kg/kg) and P partial factor productivity (104.7 kg/kg) significantly increased by 119.6% and 112.2% in RF compared to FF. Grain N, P, and K concentrations were similar in FF and RF. When the soil available P was <15 mg/kg, 15–20 mg/kg, and >30 mg/kg, readily available K was 156, 171, and 200 mg/kg, respectively. Wheat yield significantly decreased without P application. However, no yield reduction was observed when soil available P was 20–25 and 25-30 mg/kg with 147 and 158 mg/kg soil readily available K. An increase in the soil available P led to a corresponding increase in grain P concentration and a decrease in grain N concentration. The grain K concentration reached the highest value when available P was 20–25 mg/kg.

  Conclusions  In northern China, high soil available P may deteriorate the N nutrition of wheat. Reducing P fertilizer rate could promote wheat yield and increase fertilizer P efficiency. 20–30 mg/kg soil available P is suitable for enhancing high wheat yield under reduced or no P application. Wheat yield may decline without P fertilization when soil available K is higher than 170 kg/hm². Therefore, the P fertilizer application rate should be recommended based on the target of wheat yield, grain nutrient concentration, and soil available P and K. This could help rationalize fertilizer application, stabilize yield, improve quality, efficiency and green agricultural production of wheat in northern China.