Abstract:
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.
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