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Winter wheat production in the North China Plain (NCP) relies mainly on irrigation. To assess the effect irrigation management practices on crop production, the HYDRUS-1D model was modified by incorporating the crop growth module adopted from the EPIC model. The modified HYDRUS-1D model was calibrated and validated by using data collected from 2006/2007 and 2007/2008 winter wheat growing seasons in Beijing area. The predicted values for soil water content, soil nitrate concentration, crop growth, yield, and evapotranspiration showed good agreements with the measured values. The calibrated model was then used to evaluate the yield and water use efficiency (WUE) under different hydrologic years. The WUE for different irrigation depth was considered as the criterion for investigating the appropriate irrigation management practices. Results showed that the appropriate irrigation depth per application could be determined as 62.5% of the difference between 20 cmpan evaporation and precipitation for hydrologic years with 75%, 50% and 25% probability of rainfall occurrence, respectively, under the recommended nitrogen application rate in Beijing area. And the corresponding total irrigation amount was 244.7, 213.8 and 192.5 mm. The results of this study provide scientific implications for water management of winter wheat under sprinkler irrigation in the NCP and those areas with similar climatic and cropping practice conditions. [ABSTRACT FROM AUTHOR]

Low quality water has been widely used for irrigation all over the world due to water shortage. However, the use of low quality water may cause accumulation of salt in root-zone soils, resulting in poor nitrogen utilization by crops. The objective of the present study was to investigate the effects of sodium chloride (NaCI) on mineralization and nitrification of soils in the North China Plain (NCP). The experiments were conducted with laboratory incubators at 30CC. Five levels of NaCl-salt concentrations 0%, 2%, 3%, 5% and 8% in the added solutions were used in the soil samples collected from NCP. The mineralization at NaCl-salt concentration lower than 3% was not significantly different from that of the control, whereas, significant inhibition of mineralization was found in the treatments with NaCI-salt concentration higher than 3%. The inhibition of mineralization was attributed to the retardation of nitrification in relatively high salt content because ammonification was not depressed by the added NaC1 salt. The gas losses and nitrification were found decreasing with the increase in salinity. It was also found that the nitrification was more sensitive to salinity than the mineralization. Nitrification of soil samples was inhibited by 44.72%, 57.87%, and 83.64% compared with the control after 38 days of incubation at NaCI-salt concentrations of 3%, 5% and 8%, respectively. The time dependence of both the mineralization and nitrification can be fitted into a first-order kinetic model. The rate constant of mineralization and nitrification decreased exponentially with the salt content in the soils. The results of the present research may provide some scientific implications for the use of saline water or treated sewage water in the farming regions of the NCP. [ABSTRACT FROM AUTHOR]

Abstract: The North China Plain (NCP) is one of the main productive regions for winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.) in China. However, water-saving irrigation technologies (WSITs), such as sprinkler irrigation technology and improved surface irrigation technology, and water management practices, such as irrigation scheduling have been adopted to improve field-level water use efficiency especially in winter wheat growing season, due to the water scarcity and continuous increase of water in industry and domestic life in the NCP. As one of the WSITs, sprinkler irrigation has been increasingly used in the NCP during the past 20 years. In this paper, a three-year field experiment was conducted to investigate the responses of volumetric soil water content (SWC), winter wheat yield, evapotranspiration (ET), water use efficiency (WUE) and irrigation water use efficiency (IWUE) to sprinkler irrigation regimes based on the evaporation from an uncovered, 20-cm diameter pan located 0–5cm above the crop canopy in order to develop an appropriate sprinkler irrigation scheduling for winter wheat in the NCP. Results indicated that the temporal variations in SWC for irrigation treatments in the 0–60-cm soil layer were considerably larger than what occurred at deeper depths, whereas temporal variations in SWC for non-irrigation treatments were large throughout the 0–120-cm soil layer. Crop leaf area index, dry biomass, 1000-grains weight and yield were negatively affected by water stress for those treatments with irrigation depth less than 0.50E, where E is the net evaporation (which includes rainfall) from the 20-cm diameter pan. While irrigation with a depth over 1.0E also had negative effect on 1000-grains weight and yield. The seasonal ET of winter wheat was in a range of 206–499mm during the three years experiments. Relatively high yield, WUE and IWUE were found for the irrigation depth of 0.63E. Therefore, for winter wheat in the NCP the recommended amount of irrigation to apply for each event is the total 0.63E that occurred after the previous irrigation provided total E is in a range of 30–40mm. [Copyright &y& Elsevier]