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Spring wheat–summer maize (SWSM) annual crop systems were formed to satisfy the maize grain mechanized harvest thermal requirement in the thermal–resource–limited region of the North China Plain. However, the nitrogen (N) application rate effect on SWSM annual yield formation, N accumulation and utilization were barely evaluated. Two–year field experiments were conducted to evaluate the effects of the N application rate on the annual yield of SWSM, observe N accumulation and utilization, and identify the optimized N application. The experiments were conducted under 5 N levels of 0 (N0), 180 (N180), 240 (N240), 300 (N300), and 360 (N360) kg ha−1. The results showed that spring wheat, summer maize and annual cereal yield under the N240 and N480 treatments obtained the highest grain yield (GY) of 5038, 1282 and 16,320 kg ha−1, respectively, and the optimal N application rate was estimated using a linear–plateau model to be 231–307, 222–337 and 463–571 kg ha−1 with maximum GY of 4654–5317, 11,727–12,003 and 16,349–16,658 kg ha−1, respectively. With the increase in the N application rate, the dry matter accumulation (DM) were significantly increased by 16.9–173.5% for spring wheat and 11.1≈–76.8% for summer maize, respectively; and the annual cereal DM was 15.1–179.7% greater than that with N0 treatment, respectively. Spring wheat, summer maize and the annual cereal total N accumulation (TN) under N360 and N720 treatments were significantly increased by 5.4–19.1%, 16.6–32.3% and 11.5–26.2%, respectively, compared to the other treatments; however, N use efficiency for biomass and grain production (NUEbms and NUEg) were decreased significantly by 10.9–13.6% and 8.9–20.7%, 6.8–13.8% and 12.2–15.6%, and 5.5–11.7% and 10.0–16.0%, respectively. Meanwhile, the N partial factor productivity (PFPN), N agronomy use efficiency (ANUE), N recovery efficiency (NRE) and N uptake efficiency (NEupk) under the N240 treatment for spring wheat and summer maize obtained high levels of 20.99 and 47.01 kg−1, 9.27 and 16.35 kg−1, 32.53% and 32.44%, and 0.85 and 0.72 kg−1, respectively. Correlation analysis showed that the N application rate, TN and NEupk played significantly positive roles on GY, spring wheat spilke grain number, summer maize ear grain number and 1000–grain weight, DM LAImax and SPADmax, while NUEbms, NUEg, PFPN and ANUE always played negative effects. These results demonstrate that spring wheat, summer maize and annual cereal obtained the highest GY being 4654–5317, 11,727–12,003 and 16,349–16,658 kg ha−1 with the optimal N application rate 231–307, 222–337 and 463–571 kg ha−1, respectively, which provide N application guidance to farmer for spring wheat–summer maize crop systems to achieve annual mechanical harvesting in the thermal–resource–limited region of the North China Plain. [ABSTRACT FROM AUTHOR]

Soil CO 2 emissions respond differently to different tillage practices. However, limited information is available regarding the impact of conventional tillage (CT) and no-tillage (NT) on soil CO 2 emissions and the primary controlling factors or processes. The goal of this study is to derive the relationship of soil CO 2 emissions with soil physicochemical properties from differently tilled soils in a typical winter wheat summer maize rotation system. We hypothesized that soil tillage practices would impact the soil carbon cycle by modifying soil physical and chemical properties, which would in turn affect the soil CO 2 emissions. The study was conducted from 2018 to 2022 with two tillage practices using a randomized complete block design with three replicates. A leading international real-time monitoring system in situ was used to collect soil CO 2 emission data. Cumulative soil CO 2 emissions were reduced by 28.7% in maize and increased by 9.0% in wheat under NT as compared to CT. On an annual scale, the cumulative CO 2 emissions were decreased by 20.5% in NT as compared to CT. Maize season accounted for 70% 78% of soil CO 2 emissions. NT improved the aboveground biomass by 7.74% and 6.44%, and grain yields by 10.2% and 4.49% for maize and wheat, respectively. The soil CO 2 emission intensity of maize was reduced by 35.9% under NT as compared to CT. No significant differences were discovered under the two tillage practices for soil CO 2 emission intensity of wheat. For maize, NT increased the bulk density, subsequently decreasing soil temperature and increasing soil moisture. NT also led to higher soil organic carbon and total nitrogen content, ultimately resulting in a significant reduction in soil CO 2 emissions. For wheat, NT increased soil bulk density, further increasing soil moisture and lowering soil pH. NT thus resulted in lower soil organic carbon and total nitrogen content, ultimately leading to enhanced soil CO 2 emissions. Some of these observations might not be consistent with theoretical predictions, which indicated that the unconsidered factors of actual field conditions might have much significant effects. Overall, NT can be extensively used as an eco-friendly cropland tillage practice based on its positive effects of reducing CO 2 emissions and increasing crop yields. [Display omitted] • CO 2 emission variations by tillage were evaluated by the structural equation model. • No-tillage (NT) decreased CO 2 emissions by 28.7% in maize and increased by 8.99% in wheat. • Annual CO 2 emissions were decreased by 20.5% under NT than conventional tillage (CT). • Maize season accounted for 70% 78% of soil CO 2 emissions. • CO 2 emission intensity of maize was reduced by 35.9% under NT compared with CT. [ABSTRACT FROM AUTHOR]

Abstract: Wheat–maize double cropping is the most important cropping system on the Hebei Plain and is one of the most important cropping systems in China. In a scenario of greater food demand, and increasing water and rural labour scarcity, it is critical that the annual productivity of the system is improved in water-energy-cost efficient and low carbon ways. Based on farm surveys, this paper benchmarked the performance of wheat–maize double crops on the Hebei Plain during the 2004–2005 season. These farm yields were assessed both against experimental yields collected from on-farm maximum yield trials conducted during the same 2004–2005 season and relative to simulated estimates of the climate-driven potential productivity of the region. The survey of 362 farms in six counties of the Hebei Plain during the 2004–2005 season found wheat yields ranging from 3375kgha−1 to 9000kgha−1 with an overall average yield of 6556kgha−1. Maize yields averaged 7549kgha−1 and ranged from 3375kgha−1 to 11,250kgha−1. The aggregate production for the wheat–maize double crops grown in the 2004–2005 season averaged 14,105kgha−1 across the six counties. This was 72% of the average production (19,586kgha−1) recorded from on-farm trials conducted in each of the six counties and 60% of the simulated average production potential (24,147kgha−1) for the Hebei Plain in the 2004–2005 season. Thus, the annual productivity of the current cropping system could be increased with currently available technologies by 28%, while a yield increase of 42% is possible if farm yields approach the simulated yield potential. Based on farmer interviews and field observations, a number of real and perceived reasons for the current yield gaps in farmers’ fields were recognised. For instance, irrigation at stem-elongation of wheat is a current recommendation, yet only a proportion of the surveyed farmers were able to follow this strategy due to lack of access to shared irrigation facilities. Improving the region''s infrastructure to enable more timely irrigation of crops will be a necessary prerequisite to improved productivity. The results from the farm surveys and on-farm trials indicate that, with current recommended practices, farmers can improve their annual farm productivity and close the current yield gaps. However, the survey identified that increasing system performance and efficiency will require a focus on both agronomic and socio-economic issues. [Copyright &y& Elsevier]

• Future climate warming led to advance in wheat and maize phenology. • Future climate change had negative impact on maize but positive impact on wheat. • Crop water consumption was largely decreased under future climate scenarios. • Future climate change could mitigate groundwater overdraft across NCP. Climate change has already and will continue to exert a vital impact on crop yield and water use in the North China Plain (NCP). Currently, this plain is facing a dilemma between groundwater depletion and grain production demand. It is urgent to identify the impact of future climate change on crop yield and water consumption and then develop efficient adaptation strategies in the region. In this study, we used statistically downscaled daily climate data from 33 global climate models (GCMs) and two Representative Concentration Pathways (RCP4.5 and RCP8.5) for 61 stations distributed across the NCP and drove the well-validated APSIM model to simulate crop yield and water use for two future periods of 2031–2060 (2040s) and 2071–2100 (2080s). Data from all 33 GCMs show an increase in annual mean temperature and almost all the GCMs also show increases in annual mean solar radiation and annual total precipitation across the NCP. Future climate warming led to an advance in phenology for both winter wheat and summer maize, two typical crops in the NCP. However, the length of the reproductive growth period (RGP) of winter wheat was prolonged while that of summer maize was shortened under future climate scenarios across the NCP. Our simulated results show that future climate change had negative impacts on maize yield but positive impacts on wheat yield across the NCP. Mainly due to the shortening of the whole growth period, crop water consumption was largely decreased under future climate scenarios. The amount of irrigation required was also reduced mainly due to increased precipitation and decreased ET. Although future climate change would likely mitigate groundwater overdraft in most part of NCP, some areas in the northern NCP still had groundwater over-pumping in the future. Therefore, we suggest that it might be a good choice to change cropping system for reducing planting area of water-consuming crop (e.g. winter wheat) in those over-pumping areas to balance groundwater use and crop yield. [ABSTRACT FROM AUTHOR]

• Regional simulation of nitrate leaching from NCP croplands was done using NLEAP-GIS. • Spatial-temporal variation of nitrate leaching in North China Plain was quantified. • Water input, fertilizer and soil jointly affect N leaching spatial-temporal pattern. • Optimal fertilizer N rates were recommended for winter wheat-summer maize rotation. • Spatial distribution of potential groundwater nitrate pollution risk was implied. Identifying the regional characteristics of nitrate leaching from croplands is of great importance when attempting to assess the groundwater contamination risk due to nitrate leaching from croplands. The regional scale model in the Nitrogen Loss and Environmental Assessment Package with GIS Capabilities (NLEAP-GIS), which takes spatial variations in soil profile properties, meteorological data, and farm practices into account, was adopted in this study to simulate the occurrence dynamics and spatial pattern of nitrate leaching downwards through the crop root zone (0–100 cm) in winter wheat (Triticum aestivum L.)-summer maize (Zea mays L.) rotation croplands during 2011 and 2012 across the Jing-Jin-Ji region on the North China Plain (NCP). The results showed that the monthly nitrate leaching occurrences were driven by rainfall, irrigation, and fertilizer application. The simulated large spatial variation in cumulative nitrate leaching was positively correlated with both rainfall and fertilizer N application rates, whereas it was negatively correlated with N use efficiency. The cumulative nitrate leaching was mostly lower than 10 kg N ha–1 during the winter wheat growing season, whereas nitrate leaching during the summer maize growing season was much higher and mostly ranged from 20 to 100 kg N ha–1. The average cumulative nitrate leaching in the winter wheat-summer maize rotation system was 55.7 ± 33.5 kg N ha–1, accounting for 17.2 ± 10.2 % of the fertilizer N applied (average 176.3 ± 86.2 kg N ha–1 during each crop season). Fertilizer N application rates of 100–200 kg N ha–1 are recommended during each winter wheat and summer maize season to simultaneously achieve higher grain yields, greater N use efficiency, and a lower groundwater nitrate pollution risk on the NCP. The simulated spatial variation in nitrate leaching implied that there was a potential nitrate groundwater contaminant source and the results contributed to the spatial distribution assessment of groundwater nitrate contamination risk caused by fertilizer N inputs. [ABSTRACT FROM AUTHOR]