The North China Plain (NCP) is experiencing serious groundwater level decline and groundwater nitrate contamination due to excessive water pumping and application of nitrogen (N) fertilizer. In this study, grain yield, water and N use efficiencies under different cropping systems including two harvests in 1 year (winter wheat–summer maize) based on farmer (2H1Y)^FP and optimized practices (2H1Y)^OPT, three harvests in 2 years (winter wheat–summer maize–spring maize, 3H2Y), and one harvest in 1 year (spring maize, 1H1Y) were evaluated using the water-heat-carbon-nitrogen simulator (WHCNS) model. The 2H1Y^FP system was maintained with 100% irrigation and fertilizer, while crop water requirement and N demand for other cropping systems were optimized and managed by soil testing. In addition, a scenario analysis was also performed under the interaction of linearly increasing and decreasing N rates, and irrigation levels. Results showed that the model performed well with simulated soil water content, soil N concentration, leaf area index, dry matter, and grain yield. Statistically acceptable ranges of root mean square error, Nash–Sutcliffe model efficiency, index of agreement values close to 1, and strong correlation coefficients existed between simulated and observed values. We concluded that replacing the prevalent 2H1Y^FP with 1H1Y would be ecofriendly at the cost of some grain yield decline. This cropping system had the highest average water use (2.1 kg m⁻³) and N use efficiencies (4.8 kg kg^–1) on reduced water (56.64%) and N (81.36%) inputs than 2H1Y^FP. Whereas 3H2Y showed insignificant results in terms of grain yield, and 2H1Y^FP was unsustainable. The 2H1Y^FP system consumed a total of 745 mm irrigation and 1100 kg N ha^–1 in two years. When farming practices were optimized for two harvests in 1 year system (2H1Y)^OPT, then grain yield improved and water (18.12%) plus N (61.82%) consumptions were minimized. There was an ample amount of N saved, but water conservation was still unsatisfactory. However, considering the results of scenario analyses, it is recommended that winter wheat would be cultivated at <200 mm irrigation by reducing one irrigation event.

Drip irrigation under film mulching is widely promoted to replace traditional border irrigation in order to meet water saving demand in arid and semiarid regions. Our study aims to investigate quantitatively the change in crop yield, water-use efficiency (WUE) and nitrogen-use efficiency (NUE) under film mulching drip irrigation. We conducted a 4-year contrastive experiment containing two treatments on flux measurement: (1) border irrigation (BI) under film mulching; (2) drip irrigation (DI) under film mulching. Soil water and nitrate transport and utilization in the Soil–Plants–Atmosphere Continuum system, and crop dry matter were all simulated based on an integrated model of a soil-crop system: water, heat, carbon and nitrogen simulator (WHCNS). Results showed soil water content (SWC), soil ${\mathrm{N}\mathrm{O}}_3^{-}$-N content, evapotranspiration (ET), and crop dry matter (Wtotal) produced by the model were in agreement with those measured. Our study showed the irrigation and nitrogen input and output were significantly changed after BI was replaced by DI. Compared with BI treatment, DI treatment decreased ET consumption by 9% annually over four years, while it increased WUE and NUE on the farmland on average by about 28% and 39% yearly. The increase of WUE and NUE were mainly due to a significant decrease of about 56% and 68% in water and nitrogen leakage loss in DI treatment, respectively, during 2014–2017. Our study confirmed the economic and environmental benefits of the DI technology and showed its improvement prospect in the research field. Meanwhile, the results contributed to the improvement and more effective application of DI in a larger region, and provided a data basis for further study on water and fertilizer saving characteristics of DI technology.

Planting a deep-rooted green manure (GM) (more than 1.0 m depth) greatly improves soil fertility and reduces the loss of nutrients. However, few studies have examined the response of soil nitrogen (N) distribution in the soil profile and subsoil N recovery to the long-term planting and incorporation of deep-rooted GM. Based on a 12-year (2009–2021) experiment of spring maize-winter GMs rotation in the North China Plain (NCP), this study investigated the effects of different GMs that were planted over the winter, including ryegrass (RrG, Lolium L.) (>1.0 m), Orychophragmus violaceus (OrV, Orychophragmus violaceus L.) (>0.8 m), and hairy vetch (VvR, Vicia villosa Roth.) (>1.0 m), on the spring maize yield, N distribution in the deep soil profile, N use efficiencies, functional gene abundances involving soil nitrification–denitrification processes and N₂O production. Compared with the winter fallow, the maize yield significantly increased by 11.6% after 10 years of green manuring, and water storage in 0–200 cm soil profile significantly increased by 5.0–17.1% at maize seedling stage. The total N content in the soil layer at 0–90 cm increased by 15.8–19.7%, while the nitrate content in the deep soil layer (80–120 cm) decreased by 17.8–39.6%. Planting GM significantly increased the N recovery rate (10.4–32.7%) and fertilizer N partial productivity (4.6–13.3%). Additionally, the topsoil N functional genes (ammonia-oxidizing archaea amoA, ammonia-oxidizing bacterial amoA, nirS, nirK) significantly decreased without increasing N₂O production potential. These results indicated that long-term planting of the deep-rooted GM effectively reduce the accumulation of nitrates in the deep soil and improve the crop yield and N use efficiencies, demonstrating a great value in green manuring to improve the fertility of the soil, increase the crop yield, and reduce the risk of N loss in NCP.