The effects of the combined application of organic and inorganic fertilizers on the annual balance of nitrogen and phosphorus in farmlands

The loss of nitrogen and phosphorus and their environmental impacts have global relevance. The loss of nitrogen and phosphorus threatens aquatic organisms but also poses a potential threat to the human living environment and health. This issue mainly stems from the extensive use of these elements in agricultural activities. Agriculture is the main consumer of nitrogen and phosphorus globally, and excessive use of nitrogen and phosphorus fertilizers has led to serious pollution problems. This study examined the source control of nitrogen and phosphorus loss mechanisms through reducing fertilizer levels and combining organic and inorganic fertilizers in wheat‒rice double-cropping fields. Field plot experiments were carried out for ten consecutive years (2014-2023), and three treatments were set up: conventional fertilization (CK), fertilizer reduction (10% reduction in seasonal nitrogen and phosphorus in wheat, 15% reduction in seasonal nitrogen and phosphorus in rice) (KF), and combined application of organic and inorganic fertilizer (BMP). This article only analyzes data related to 2023. Compared with CK treatment, BMP treatment reduced the average mass concentration of total nitrogen (TN) and total phosphorus (TP) in the runoff water by 10.92% and 7.96%, respectively. Compared with CK treatment, BMP treatment in leached water reduced the average mass concentration of total nitrogen (TN) by 14.65% and 11.00%, and total phosphorus (TP) by 22.63% and 4.99% in wheat and rice seasons, respectively. Compared with those of CK, the TN contents of wheat and rice treated with BMP significantly decreased by 22.39% and 14.86%, and the TP losses decreased by 20.00% and 12.98%, respectively. The implications of these findings are promising: the combined application of organic and inorganic fertilizers in the wheat‒rice rotation mode can ensure crop yield, increase soil nutrient retention, reduce nitrogen and phosphorus loss, and maintain the soil nutrient balance.