The North China Plain is an important irrigated agricultural area in China. However, the effects of irrigation management on carbon emission are not well documented in this region. Due to the uneven seasonal distribution of rainfall, irrigation is mainly concentrated in the winter wheat growing season in the North China Plain. In this study, we estimated CO₂ emission and soil CH₄ uptake from winter wheat fields with different irrigation methods and scheduling treatments using the static chamber-gas chromatography method from April to May 2017 and 2018. Treatments included three irrigation methods (surface drip, sprinkler, and border) and three irrigation scheduling levels that initiated as soon as the soil moisture drained to 50%, 60%, and 70% of the field capacity for a 0–100 cm soil profile were tested. The results showed that both the irrigation methods and scheduling significantly influenced (p < 0.05) the cumulative CO₂ and CH₄ emission, grain yield, global warming potential (GWP), GWP Intensity (GWPI), GWPI per unit irrigation applied, and water use efficiency (WUE). Compared to 60% and 70% FC, 50% FC irrigation scheduling de-creased accumulated CH₄ uptake 26.8–30.3% and 17.8–25.4%, and reduced accumulated CO₂ emissions 7.0–15.3% and 12.6–19.4%, respectively. Conversely, 50% FC reduced GWP 6.5–13.3% and 12.5–19.4% and lower grain yield 10.4–19.7% and 8.5–16.6% compared to 60% and 70% FC irrigation scheduling in 2017 and 2018, respectively. Compared to sprinkler irrigation and border irrigation, drip irrigation at 60% FC increased the accumulated CH₄ uptake 11.3–12.1% and 1.9–5.5%, while reduced the accumulated CO₂ emissions from 7.5–8.8% and 10.1–12.1% in 2017 and 2018, respectively. Moreover, drip irrigation at 60% FC increased grain yield 5.2–7.5% and 6.3–6.8%, WUE 0.9–5.4% and 5.7–7.4%, and lowered GWP 8.0–9.8% and 10.1–12.0% compared to sprinkler and border irrigation in 2017 and 2018, respectively. The interaction of irrigation scheduling and irrigation methods significantly impacted accumulated CH₄ uptake, cumulative CO₂ amount, and GWP in 2018 only while grain yield and WUE in the entire study. Overall, drip irrigation at 60% FC is the optimal choice in terms of higher grain yield, WUE, and mitigating GWP and GWPI from winter wheat fields in North China Plain.

Soil salinization adversely affects agricultural productivity. Mitigating the adverse effects of salinity represents a current major challenge for agricultural researchers worldwide. The effects of exogenously applied glycine betaine (GB) and salicylic acid (SA) on mitigating sodium toxicity and improving the growth of cotton seedlings subjected to salt stress remain unclear. The treatments in a phytotron included a control (CK, exogenously untreated, non-saline), two NaCl conditions (0 and 150 mM), four exogenous GB concentrations (0, 2.5, 5.0, and 7.5 mM), and four exogenous SA concentrations (0, 1.0, 1.5, and 2.0 mM). The shoot and roots exposed to 150 mM NaCl without supplementation had significantly higher Na⁺ and reduced K⁺, Ca²⁺, and Mg²⁺ contents, along with lowered biomass, compared with those of CK. Under NaCl stress, exogenous GB and SA at all concentrations substantially inversed these trends by improving ion uptake regulation and biomass accumulation compared with NaCl stress alone. Supplementation with 5.0 mM GB and with 1.0 mM SA under NaCl stress were the most effective conditions for mitigating Na⁺ toxicity and enhancing biomass accumulation. NaCl stress had a negative effect on plant growth parameters, including plant height, leaf area, leaf water potential, and total nitrogen (N) in the shoot and roots, which were improved by supplementation with 5.0 mM GB or 1.0 mM SA. Supplementation with 5.0 mM exogenous GB was more effective in controlling the percentage loss of conductivity (PLC) under NaCl stress.

Long−term excessive nitrogen fertilizer input has resulted in several environmental problems, including an increase in N₂O emissions and the aggravation of nitrate leaching; monitoring nitrogen fertilizer is crucial for maize with high yield. This study aimed to optimize the amount of nitrogen applied to maize by Climate−Smart Agriculture (CSA) so as to continuously improve agricultural productivity and reduce or eliminate N₂O emissions as much as possible. Field experiments with a completely randomized design were conducted to examine the effects of six nitrogen treatments (N application levels of 0, 120, 180, 240, 300, 360 kg·ha⁻¹, respectively) on N₂O emissions, residual concentration of nitrate and ammonium nitrogen, maize yield, and nitrogen utilization efficiency in 2018 and 2019. The results indicated that the residual concentration of nitrate nitrogen (${\mathrm{NO}}_3^{-}$−N) in the two seasons significantly increased; N₂O emissions significantly increased, and the nitrogen fertilizer agronomic efficiency and partial productivity of maize fell dramatically as the nitrogen application rate increased. The maize grain yield rose when the N application amount was raised (N application amount 300 kg·ha⁻¹. An increase in the nitrogen application rate can decrease nitrogen use efficiency, increase soil ${\mathrm{NO}}_3^{-}$−N residual, and N₂O emissions. Reasonable nitrogen application can increase maize yield and reduce N₂O emissions and be conducive to improving nitrogen use efficiency. By considering summer maize yield, nitrogen use efficiency, and farmland ecological environment, 173.94~178.34 kg N kg·ha⁻¹ could be utilized as the nitrogen threshold for summer maize in the North China Plain.

Saline water irrigation has been widely used for crop production where agriculture is short of freshwater. However, information about the response of soil respiration to saline water irrigation is limited. To identify the effect of saline water irrigation on soil respiration, the experiment based on long-term saline water irrigation cotton fields (since 2006) was conducted in the Heilonggang area in 2021. Five salinity levels in irrigation water were tested (3.4 [S1], 7.1 [S2], 10.6 [S3], 14.1 [S4], and 17.7 dS m⁻¹ [S5]), and deep ground water (1.3 dS m⁻¹) was used as the control (CK). After 15 years of saline water irrigation, we monitored soil physicochemical properties and soil respiration. In addition, we developed a structural equation model of the relationship between them. The results demonstrated that saline water irrigation significantly reduced soil water-stable aggregate content and porosity by 4.42–45.33% and 6.52–14.10%, respectively, and attenuated soil cellulase, α-glucosidase, and alkaline phosphatase activity. Soil respiration under saline water irrigation was significantly reduced by 5.28–33.08%. Moreover, saline water irrigation with salinity below 10.6 dS m⁻¹ had no significant effect on cotton yield. Moreover, soil salinity (62%), water-stable aggregate content (46%), and soil porosity (25%) had significant effects on soil respiration, and soil porosity had a significant positive effect on soil alkaline phosphatase activity according to the structural equation model. Overall, saline irrigation with salinity below 10.6 dS m⁻¹ can alleviate water shortages and reduce soil carbon emissions without affecting cotton yield in the study area.

The North China Plain (NCP) produces about half of the winter wheat yield in China; therefore, it is essential to improve winter wheat grain yield, biomass, and water productivity (WP) under current water shortage conditions in this area. In this study, the AquaCrop model was used for calibrating and validating crop canopy cover, grain yield, biomass, soil water content, crop evapotranspiration (ET_C), and crop WP under an irrigation scheduling of 50%, 60%, and 70% field capacities with sprinkler irrigation, drip irrigation, and flood irrigation methods for winter wheat crop. The model was calibrated employing experimental data for the 2016–2017 winter wheat season and, subsequently, validated with using data from 2017–2018. The model performance was analyzed using root-mean-square error (RMSE), normalized root-mean-square error (NRMSE), the coefficient of determination (R²), and Willmott’s index of agreement (d). The prediction error between the simulated and observed values for grain yield, biomass, soil water content, ET_C, and WP were the minimum at a 60% field capacity and the maximum at a 50% field capacity irrigation scheduling. The model simulation was satisfactory under the 60% and 70% field capacity irrigation scheduling, while the model performance was relatively low under the 50% field capacity irrigation scheduling. Irrigation to 4–5 times the 30 mm depth (total 120–150 mm) by drip irrigation and sprinkler irrigation was the most effective irrigation schedule to obtain the optimum grain yield, biomass, and WP on the NCP. Our findings suggest that the AquaCrop model could be a feasible tool for precisely simulating the canopy cover, grain yield, biomass, soil water content, ET_C, and WP of winter wheat under different irrigation schedules and irrigation methods on the NCP with higher certainty than under current practices.