Nitrous oxide (N₂O) and ammonia (NH₃) volatilization (AV) are the major pathways of nitrogen (N) loss in soil, and recently, N₂O and NH₃ mitigation has become urgently needed in agricultural systems worldwide. However, the influence of straw incorporation (SI) and biochar addition (BC) on N₂O and NH₃ emissions are still unclear. To fill this knowledge gap, a soil column experiment was conducted with two management strategies using straw ‐ straw incorporation (S1) and straw removal (S0) ‐ and four biochar application rates (0 (C0), 15 (C1), 30 (C2), and 45 t ha⁻¹ (C3)) to evaluate the impacts of their interactions on N₂O and NH₃ emissions. The results showed that NO₃⁻−N concentration and pH was the major contributors to affect the N₂O and NH₃ losses. Without biochar addition, N₂O emissions was decreased by 59.6% (P<0.05) but AV was increased by 97.3% (P<0.05) under SI when compared to SR. Biochar was beneficial for N₂O mitigation when straw was removed, but increased N₂O emission by 39.4%−83.8% when straw was incorporated. Additionally, biochar stimulated AV by 27.9%−60.4% under S0 and 78.6%−170.3% under S1. Consequently, SI was found to significantly interact with BC in terms of affecting N₂O (P<0.001) and NH₃ (P<0.001) emissions; co-application of SI and BC promoted N₂O emissions and offset the mitigation potential by SI or BC alone. The indirect N₂O emissions caused by AV, however, might offset the reduction of direct N₂O caused by SI or BC, thus leading to an increase in overall N₂O emission. This paper recommended that SI combined BC at the amount of 8.2 t ha⁻¹ for maintaining a lower overall N₂O emission for future agriculture practices, but the long-term impacts of straw incorporation and biochar addition on the trade-off between N₂O and NH₃ emissions and reactive N losses should be further examined and assessed.

To address water scarcity, environmental pollution from excessive fertilization, and the need for stable grain yields in the North China Plain (NCP), a 3-year field experiment (2021–2024) was conducted to explore the effects of water and nitrogen (N) management under subsurface drip irrigation on winter wheat–summer maize rotation system. This study included three irrigation treatments (irrigated to 80% (D1), 75% (D2), and 70% (D3) of field water-holding capacity (WHC) when soil water content dropped below 65%, 60%, and 55% of WHC, respectively) under N210 and four N application rates (0 (N0), 150 (N150), 210 (N210), and 270 (N270) kg N ha⁻¹ for each season) under D1. The results showed that D1 and N210 all significantly improved leaf area index (LAI) and aboveground biomass by reducing chlorophyllase and pheophytinase activities (delaying leaf senescence) and enhancing nitrate reductase (NR), glutamine synthetase (GS), and glutamate synthase (GOGAT) activities (promoting N assimilation). Furthermore, compared with D3, D1 increased winter wheat and summer maize yields by 12.7% and 24.3%, respectively, and improved partial factor productivity (PFP) by 14.0–46.0%. Redundancy analysis (RDA) and structural equation modeling confirmed that LAI, biomass, and N-transforming enzyme activities were the key drivers of yield. This study demonstrated that the combination of D1 and N210 treatments were the optimal water and N fertilizer management strategies for achieving water conservation, N reduction, and stable high yields in drip-irrigated rotation systems of the NCP.

Unreasonable nitrogen (N) management and the shortage of groundwater resources are prominent problems faced by intensive farmland in North China. The main processes to reduce N₂O emissions under drip irrigation still need to be further explored. This study conducted a three-year field experiment (2021–2024) of wheat–maize cropping system in Hebei Province to study the effects of four N levels under drip irrigation (i.e., N0: no N applied; N150: 150 kg N ha⁻¹; N210: 210 kg N ha⁻¹; N270: 270 kg N ha⁻¹) on yield, N₂O emission, soil carbon (C) and N fractions, enzymes, and N functional genes. The results showed that N rate significantly affected N₂O emissions (p < 0.05). The highest value of N₂O emissions (10.64 kg N ha⁻¹) over three years and yield-scale N₂O emissions (0.25 g kg⁻¹) were found under N270, which were 32.1% and 78.6% higher than those of N210. No significant difference in annual yields between N210 and N270 was found, but the annual yield of N150 was decreased by 14.4% as compared to N210. N rate significantly affected soil C-N fractions and enzymes, in which NO₃⁻-N, MBC, DON, amoA-AOB, and UE enzymes, as the major factors of soil properties, N functional genes, and enzymes affecting N₂O emissions, were more favorably regulated along with the increase in fertilizer N rate. Correlation analysis indicated that amoA-AOB was significantly correlated to N fractions (i.e., NH₄⁺-N, NO₃⁻-N, TN, DON and MBN) and UE enzymes. Structural equation modeling further proved that an increase in fertilizer N rate directly increased enzyme activities related to N transformation, which increased N fractions, thus promoting the abundance of amoA-AOB genes involved in nitrification that stimulate N₂O emissions. Therefore, these findings underscore that N210 was an optimal fertigation strategy for minimizing N₂O emissions without compromising yield, offering a practical pathway for sustainable intensification in water-limited regions.