Optimizing phosphate application to improve soil quality and reduce phosphorus loss in rice-wheat rotation

How to determine the optimal dosage of phosphorus (P) fertilizer input for an agricultural field is important to maintain soil quality and crop production while minimizing environmental impact. In this study, we set up a 5-year rice-wheat rotation with contrasting P fertilization treatments (0, 25, 50, 75, 100, and 150 kg P₂O₅ ha⁻¹, hereafter, P₀, P₂₅, P₅₀, P₇₅, P₁₀₀, and P₁₅₀, respectively) per season to explore the relationship between the amount of P input and crop yield, P use efficiency (PUE), balance of P accumulation and loss, ecosystem multifunctionality (EMF), and soil quality. Our results indicate that increased P amounts significantly boosted rice and wheat production of both straw and grain, but the tendency slowed down when the input was over 75 kg P₂O₅ ha⁻¹. The PUE declined with increased P input and soil P balance of 50 kg P₂O₅ ha⁻¹ for wheat and 100 kg P₂O₅ ha⁻¹ for rice. Runoff emerges as the main pathway for soil P loss and escalates with higher P application rates. We emphasize increasing ridge height and controlling water input for basal fertilizer to minimize P loss. The application of P fertilizer increased the soil P pool, with labile P (L-P) and moderately labile P (M-P) increasing by 13–114 % and 23–111 %, respectively, compared to P₀. The transformation of M-P to L-P in paddy soil is associated with an increased abundance of Actinobacteria. Low P applications (P₂₅ and P₅₀) increased EMF by 3.27 and 3.58 times, while high P applications (P₇₅, P₁₀₀, and P₁₅₀) decreased EMF. Furthermore, P application significantly improved the soil quality index (SQI) compared to P₀. The impact of abiotic factors on yield and P loss is more significant than that of biotic elements, with the SQI serving as a dependable indicator for predicting yield. Central to minimizing P loss while maximizing yield is the reduction of Resin-P content and the maintenance of NaOH-P_i levels, suggesting that organic materials may be a good alternative strategy. These findings provide valuable data and theoretical support for optimizing P application in rice-wheat cropping systems, promoting a mutually beneficial scenario for agricultural production and ecological protection.