Effects of long-term phosphorus application on winter wheat yield and soil inorganic phosphorus forms in dryland

  Objectives  Due to the low efficiency of phosphorus (P) fertilizer in calcareous soil, we studied the variation of soil P forms and their availability to crop under long-term application of P fertilizer, to provide a theoretical basis for optimal P application.

  Methods  The long-term experiment, established in 2004, was located in Yangling, Shaanxi Province. The tested P₂O₅ application rates were 0, 50, 100, and 150 kg/hm². The wheat plant samples were collected during 2009, 2013, and 2017 harvesting periods for the investigation of yield and P uptake, as well as the inorganic P forms and available P in the soil at 0–20 cm depth.

  Results  Regression analysis revealed that the P₂O₅ application rate was 118 kg/hm² for the highest wheat yield (5174 kg/hm²) and the highest grain P uptake (14.5 kg/hm²). When the P₂O₅ rate reached 100 kg/hm², the Olsen-P in 0–20 cm soil layer was increased significantly by 28.9%–35.4% from 2009 to 2017, with the annual increase of 0.73 mg/kg in Olsen-P content by every 100 kg/hm² of P₂O₅ input per year. When the P₂O₅ rate exceeded 100 kg/hm², the Ca₂-P, Al-P, Fe-P and O-P contents in soil were increased significantly, and the Ca₂-P and Al-P kept increasing as experimental years progressed, while Ca₈-P was decreased. At more than 150 kg/hm² P₂O₅ rate, the Ca₁₀-P were decreased significantly compared with other treatments. The decrease in Ca₁₀-P was accompanied with increases in Ca₂-P and Olsen-P. The availability of inorganic P forms descended in order: Ca₂-P>Al-P>Ca₈-P>Fe-P>O-P> Ca₁₀-P.

  Conclusions  Without P application, there is deficit of P in calcareous soils. The Ca₂-P is mainly supplemented by Ca₈-P and Al-P. When surplus, soil P is mainly accumulated in the forms of Ca₂-P, Al-P and Ca₈-P. Based on the regression of wheat yield, P uptake and P application rate, the optimal annual P₂O₅ application rate is 118 kg/hm².