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Improving grain yield and water use efficiency (WUE) under limited irrigation is very important for food security in water shortage regions. This paper summarized a long-term field experiment (from 1987 to 2015, 28 growing seasons of winter wheat) on the responses of winter wheat to different levels of water stress under the changing background of cultivars, soil fertility and weather conditions at a site in the North China Plain (NCP). The results showed that during the past 28 seasons soil organic matter and N contents were significantly increased at the experimental site and the atmospheric evaporation demand (ET 0 ) was increased and seasonal rainfall was reduced. Although yield was continuously increased from 1987 to 2015 under irrigated condition, the yield of winter wheat under rain-fed condition decreased recently as compared with that during 2000s due to the higher ET 0 and less seasonal rainfall. WUE was increased continuously from past to present, especially under water stress condition, indicating that the winter wheat used water more efficiently under the current growing conditions. This could be attributed to the increase in harvest index, improved N status in soil and the reduced soil evaporation. Overall, the sensitivity of grain yield to the fluctuation in seasonal ET was increased from 1980s to present. Yield reduction rate under water stress was greater under current growing conditions than that back in 1980s and 1990s. However, even with the changes in the responses to water stress, irrigation scheduling of one irrigation application from recovery to jointing for winter wheat could achieve relative stable yield and higher WUE through the 28 seasons and should be taken as optimized irrigation scheduling under limited water supply condition. [ABSTRACT FROM AUTHOR]

Abstract: In the North China Plain (NCP), while irrigation using groundwater has maintained a high-level crop productivity of the wheat–maize double cropping systems, it has resulted in rapid depletion of groundwater table. For more efficient and sustainable utilization of the limited water resources, improved understanding of how crop productivity and water balance components respond to climate variations and irrigation is essential. This paper investigates such responses using a modelling approach. The farming systems model APSIM (Agricultural Production Systems Simulator) was first calibrated and validated using 3 years of experimental data. The validated model was then applied to simulate crop yield and field water balance of the wheat–maize rotation in the NCP. Simulated dryland crop yield ranged from 0 to 4.5tha−1 for wheat and 0 to 5.0tha−1 for maize. Increasing irrigation amount led to increased crop yield, but irrigation required to obtain maximum water productivity (WP) was much less than that required to obtain maximum crop yield. To meet crop water demand, a wide range of irrigation water supply would be needed due to the inter-annual climate variations. The range was simulated to be 140–420mm for wheat, and 0–170mm for maize. Such levels of irrigation applications could potentially lead to about 1.5myear−1 decline in groundwater table when other sources of groundwater recharge were not considered. To achieve maximum WP, one, two and three irrigations (i.e., 70, 150 and 200mmseason−1) were recommended for wheat in wet, medium and dry seasons, respectively. For maize, one irrigation and two irrigations (i.e., 60 and 110mmseason−1) were recommended in medium and dry seasons, while no irrigation was needed in wet season. [Copyright &y& Elsevier]

Abstract: Serious water deficits and deteriorating environmental quality are threatening agricultural sustainability in the North China Plain (NCP). This paper addresses spatial and temporal availability of water resources in the NCP, identifies the effects of soil management, irrigation timing and amounts, and crop genetic improvement on water use efficiency (WUE), and then discusses knowledge gaps and research priorities to further improve WUE. Enhanced irrigation and soil nutrient (mainly nitrogen) management are the focal issues in the NCP for enhancing WUE, which are shown to increase WUE by 10–25% in a wheat–maize double cropping system. Crop breeding has also contributed to increased of WUE and is expected to play an important role in the future as genetic and environmental interactions are understood better. Agricultural system models and remote sensing have been used to evaluate and improve current agronomic management practices for increasing WUE at field and regional scales. The low WUE in farmer''s fields compared with well-managed experimental sites indicates that more efforts are needed to transfer water-saving technologies to the farmers. We also identified several knowledge gaps for further increasing WUE in the NCP by: (1) increasing scientific understanding of the effects of agronomic management on WUE across various soil and climate conditions; (2) quantifying the interaction between soil water and nitrogen in water-limited agriculture for improving both water and nitrogen-use efficiency; (3) improving irrigation practices (timing and amounts) based on real-time monitoring of water status in soil-crop systems; and (4) maximizing regional WUE by managing water resources and allocation at regional scales. [Copyright &y& Elsevier]