Reducing ammonia emissions and nitrate leaching in wheat–maize systems by substituting chemical fertilizers with manure

Introduction Ammonia (NH 3 ) emissions and nitrate (NO 3 - ) leaching from crop fields are major contributors to non-point source environmental pollution. Methods To optimize the resource utilization of pig manure and reduce gaseous and liquid nitrogen losses in wheat–maize rotation systems, five treatments were investigated, including 15% (OF 15 ), 30% (OF 30 ), and 45% (OF 45 ) substitution of chemical fertilizer nitrogen with pig manure as well as a no-nitrogen control (CK) and local farmer’s fertilization method (CF). Ventilation-type NH 3 capturing devices and NO 3 - leaching lysimeters were used to systematically investigate the nitrogen (N) dynamics in the wheat–maize rotation systems from 2022 to 2024. Results The pig manure substitution ratio had profound impacts on NH 3 emissions, NO 3 - leaching, and crop yields. When the substitution ratio of pig manure was 30%, wheat produced the highest average yield at 9,181 kg ha -1 , with 0.256 g kg -1 lower NH 3 emissions per unit of grain output compared to chemical fertilization alone. Similarly, the maize yield was 10,897 kg ha -1 , with 0.17 lower NH 3 emissions per unit of grain. Discussion Comprehensive analysis suggests that 30% pig manure substitution ratio in OF 30 will be optimal to achieve environmental and yield benefits simultaneously.