Coupling effects of water and phosphate fertilizer supply on soil P availability and use efficiency

Coupling water and fertilizer supply is an efficient strategy for improving phosphate fertilizer using efficiency (PUE). However, little study has been done on interaction of phosphate fertilizer and water supply. To this end, an experiment was carried out to analyze the response of soil P mobility, dynamic changes of various inorganic P contents, corn P nutrient and PUE for two P sources acidic fluid drip irrigation fertilizer (DIF) and granular triple superphosphate (TSP) and different modes of P supply (including single application as base fertilizer and multiple application with irrigation) under simulated drip irrigation conditions in calcareous soils. The aim of the experiment was to propose the optimal strategy for efficient use of P fertilizer under drip irrigation. The results showed that 1) compared with multiple application of triple superphosphate with irrigation (TSP+split), multiple application of acidic fluid drip irrigation fertilizer (Fliud+split) significantly increased soil available P content (P < 0.05). For instance, soil average Ca₂-P and resin-P contents of different soil layers increased by 12.4% and 21.6%, respectively. Moreover, soil resin-P content decreasing percentage was lower by 56.5% in Fluid+split treatment than in TSP+split treatment in vertical soil layers. Fluid+split treatment also significantly increased P mobility (P < 0.05). 2) Compared with TSP+split treatment, the ratio of labile forms of inorganic P (including Ca₂-P, resin-P and NaHCO₃-P) to total inorganic P increased by 21.0%, while the ratio of unavailable forms of inorganic P (Ca₁₀-P and residue-P) to soil total inorganic P decreased by 10.1% in Fluid+split treatment. This indicated that soil P fixation was significantly alleviated by coupling of fluid P fertilizer and water application. 3) The biomass, absorbed P content and PUE of corn increased by 27.1%, 34.6% and 61.4%, respectively, under Fluid+split treatment compared with TSP+split treatment. In summary, coupling P fertilizer with irrigation was not only alleviating the reaction processes of soil P fixation, promoting P mobility and availability, but also improving plant P nutrient and PUE.