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.

The cycle of key nutrient elements nitrogen (N) and phosphorus (P) has been massively altered by anthropogenic activities. Little is known about the impacts on greenhouse gas (GHG) emission of the large nutrient additions occurring in the alpine grasslands of the Tibetan Plateau. We investigated soil surface emissions of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) under control, N, P and combined nitrogen and phosphorus (NP) additions from July 2011 to September 2012. Compared to the control, CO₂ flux significantly increased by 14.6% and 27.4% following P and NP addition, respectively. The interaction of NP addition had a significant influence on CO₂ flux during the non-growing season and the spring thaw period. Compared to the control, CH₄ flux decreased by 9.9%, 23.2% and 26.7% following N, P and NP additions, respectively, and no interactive effect of NP addition was found in any period. Soil N₂O flux was significantly increased 2.6 fold and 3.3 fold, following N and NP addition treatments, respectively, and there was no interaction effect of NP addition together. The contribution of cumulative CO₂ emission during the non-growing season was less than 20% of the annual budget, but cumulative CH₄ and N₂O emissions during the same period can account for 37.3–48.9% and 44.7–59.5% of the annual budget, respectively. Methane and N₂O emissions did not increase greatly during the spring thawing period, with contributions of only 0.4–3.6% and 10.3–12.3% of the annual budget, respectively. Our results suggest that N and P addition could increase CO₂ and N₂O emissions and reduce CH₄ emission. Furthermore, although the non-growing season is very cold and long, cumulative CH₄ and N₂O emissions are considerable during this period and cannot be neglected by future studies evaluating the greenhouse gas emission budget in the Tibetan plateau.

High planting density and nitrogen shortage are two important limiting factors for crop yield. Phytohormones, abscisic acid (ABA), and jasmonic acid (JA), play important roles in plant growth. A pot experiment was conducted to reveal the role of ABA and JA in regulating leaf gas exchange and growth in response to the neighborhood of plants under different nitrogen regimes. The experiment included two factors: two planting densities per pot (a single plant or four competing plants) and two N application levels per pot (1 and 15 mmol·L⁻¹). Compared to when a single plant was grown per pot, neighboring competition decreased stomatal conductance (g_s), transpiration (T_r) and net photosynthesis (P_n). Shoot ABA and JA and the shoot-to-root ratio increased in response to neighbors. Both g_s and P_n were negatively related to shoot ABA and JA. In addition, N shortage stimulated the accumulation of ABA in roots, especially for competing plants, whereas root JA in competing plants did not increase in N15. Pearson’s correlation coefficient (R²) of g_s to ABA and g_s to JA was higher in N1 than in N15. As compared to the absolute value of slope of g_s to shoot ABA in N15, it increased in N1. Furthermore, the stomatal limitation and non-stomatal limitation of competing plants in N1 were much higher than in other treatments. It was concluded that the accumulations of ABA and JA in shoots play a coordinating role in regulating g_s and P_n in response to neighbors; N shortage could intensify the impact of competition on limiting carbon fixation and plant growth directly.

Collecting accurate real-time soil moisture data in crop root zones is the foundation of automated precision irrigation systems. Soil moisture sensors (SMSs) have been used to monitor soil water content (SWC) in crop fields for a long time; however, there is no generally accepted guideline for determining optimal number and placement of soil moisture sensors in the soil profile. In order to study adequate positioning for the installation of soil moisture sensors in the soil profile, six years of field experiments were carried out in North China Plain (NCP). Soil water content was measured using the gravimetric method every 7 to 10 days during six growing seasons of winter wheat (Triticum aestivum L), and root distribution was measured using a soil core method during the key periods of winter wheat growth. The results from the experimental data analysis show that SWC at different depths had a high linear correlation. In addition, the values of correlation coefficients decreased with increasing soil depth; the coefficient of variation (CV) of SWC was higher in the surface layers than in the deeper layers (depths were 0–40 cm, 0–60 cm, and 0–100 cm during the early, middle, and last stages of winter wheat, respectively); wheat roots were mainly distributed in the surface layer. According to an analysis of CV for SWC and root distribution, the depths of planned wetted layers were determined to be 0–40 cm, 0–60 cm, and 0–100 cm during the sowing to reviving stages (the early stage of winter wheat), returning green and jointing stages (the middle stage of winter wheat), and heading to maturity stage (the last stage of winter wheat), respectively. The correlation and R-cluster analyses of SWC at different layers in the soil profile showed that SMSs should be installed 10 and 30 cm below the soil surface during the winter wheat growing season. The linear regression model can be built using SWC at depths of 10 and 30 cm to predict total average SWC in the soil profile. The results of validation showed that the developed model provided reliable estimates of total average SWC in the planned wetted layer. In brief, this study suggests that suitable positioning of soil moisture sensors is at depths of 10 and 30 cm below the soil surface.

Agricultural soils are major anthropogenic sources of N₂O emissions. The application of nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) has been proved to be an effective management measure to mitigate N₂O emissions. However, the influence mechanism of DMPP on the mitigation of soil N₂O emissions under different irrigation regimes remains unclear. Therefore, a lysimeter experiment was conducted to study the effects of irrigation level (lower irrigation limits of 75%, 65%, and 55% of field capacity (FC), signed as WH, WM, and WL) and DMPP addition (0% and 1% of N application, signed as D0 and D1) on N₂O emissions, soil environmental factors such as ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃⁻-N), water-filled pore space (WFPS), soil temperature, and the abundances of N₂O-related genes (AOA amoA, AOB amoA, nirS, and nirK). The results showed that soil N₂O emissions increased with the increasing of irrigation level. The efficiency of DMPP mitigating N₂O emissions varies depending on irrigation regime. Compared to D0, D1 strongly decreased cumulative N₂O emissions by 11.27%, 18.96%, and 15.05% in the WL, WM, and WH conditions, respectively. Meanwhile, D1 caused an obvious reduction in the AOB amoA gene by 29.73%, 47.02%, and 22.41%, respectively, but there was no significant effect on the AOA amoA gene. D1 was effective in decreasing nirS and nirK genes except in the WL condition; the percentages of reduction were 48.45%, 40.84% and 37.18%, 44.97% in the WM and WH conditions, respectively. In addition, D1 caused an increase in NH₄⁺-N content and a decrease in NO₃⁻-N content, WFPS, and soil temperature in all irrigation regimes. A higher significant correlation was observed between N₂O emissions and NH₄⁺-N and AOB amoA in the WL and WM conditions, while a significant correlation was observed between N₂O emissions and NO₃⁻-N, nirK, and nirS in the WH condition. It was revealed that with the increase in irrigation level, the main source of N₂O emissions might change from nitrification to denitrification. Overall, our study indicated that in the WL and WM conditions, the mitigation of N₂O emissions by DMPP was primarily attributable to the inhibition of the AOB amoA gene, whereas the inhibition of nirS and nirK genes was likely the dominant mechanism in the WH condition. The findings of this study will provide a theoretical basis for the application of a nitrification inhibitor for drip-irrigated winter wheat fields in the North China Plain.

Water scarcity is a key limitation to winter wheat production in the North China Plain, and it is essential to explore the optimal timing of spring irrigation to optimize N and Si uptake as well as to safeguard yields. The aim of this study was to systematically study the effect mechanism of nitrogen and silicon absorption of winter wheat on yield under spring irrigation and to provide a scientific basis for optimizing irrigation strategy during the growth period of winter wheat. In this experiment, the winter wheat ‘Heng 4399’ was used. Five irrigation periods, i.e., 0 d (CK), 5 d (AJ5), 10 d (AJ10), 15 d (AJ15), and 20 d (AJ20) after the jointing stage, were set up to evaluate the nitrogen (N) and silicon (Si) absorption and grain yield (GY). The results showed that delayed irrigation for 5–10 days at the jointing stage had increased the GY. With the delay of irrigation time, the N/Si content of the entire plant at the maturity period increased first and then decreased; among that, the maximum N contents appeared in AJ15 and AJ5 in 2015 and 2020, respectively, while the Si concentrations appeared in AJ5 and AJ10 in sequence. Compared with AJ15 and AJ20, the N accumulation of vegetative organs in AJ5 increased by 3.05~23.13% at the flowering stage, 14.12~40.12% after the flowering stage, and a 1.76~6.45% increase in the N distribution rate at maturity stage. A correlation analysis revealed that the GY was significantly and positively correlated with the N/Si accumulation at the anthesis and N translocation after the anthesis stage. In conclusion, under limited irrigation conditions, delaying watering for 5 to 10 days at the jointing stage can improve the nitrogen and silicon absorption and nutrient status of wheat plants and increase wheat yield.