Assessment of groundwater use by wheat (Triticum aestivum L.) in the Luancheng Xian region and potential implications for water conservation in the northwestern North China Plain

Agricultural sustainability in China, especially in the North China Plain, is highly dependent on water resource availability. Land management has changed dramatically in this region since the 1970's when a more intensive practice of winter wheat (Triticum aestivum L.) and summer corn (Zea mays L.) in one-year rotation started causing excessive exploitation of groundwater to meet crop water needs for high yield productivity. Over fifty percent of the area in the northwestern region of the North China Plain is irrigated using groundwater. Over ninety percent of Luancheng Xian county is in a groundwater-irrigated winter wheat---corn rotation. In addition the irrigation management practices, agricultural management practices, soil textural classes (mostly loam soils) and climate are similar throughout the Northwestern North China Plain and the Luancheng Xian county. Our objectives were to identify whether land use is a factor contributing to groundwater table decline in Luancheng Xian county of the North China Plain and to use long term small plot studies from 1998 to 2002 to evaluate the potential of limited irrigation based on wheat stage of growth as a viable water-saving practice to reduce consumptive use and stabilize the groundwater table. Assessment of groundwater resources for the Luancheng Xian county found that groundwater levels have been dropping at a rate of 0.8 m yr-1 (31.52 in yr-1) (P < 0.001). This occurred during a time of significantly lower precipitation that explained about 91 percent of the groundwater depletion rate (P < 0.001). The drop in groundwater levels was also correlated (r2 = 0.71) with the increased area planted to wheat (P < 0.001). At this current rate of groundwater use, the resource will be depleted within three decades. A more efficient management system that increases water use efficiency or amount of grain produced per unit of water use is needed for sustainability of the cropped areas. We found that irrigation scheduling based on wheat stage of growth can significantly increase water use efficiency when we target application of two key 60 mm (2.36 in) irrigation events at the jointing and heading stages of growth when compared to traditional irrigation management practices that use four irrigation events (240 mm or 9.46 in) (P < 0.05). Although simulated Penman-Monteith evapotranspiration from 1998 to 2002 was significantly correlated with measured values (P < 0.001), Penman-Monteith evapotranspiration values were higher than evapotranspiration measured with weighing lysimeters (P < 0.05). Our 1998 to 2002 studies suggest that there is potential to use stage of growth and water budget models for irrigation scheduling in the Northwestern North China Plain and cut water use by nearly fifty percent without significantly reducing grain yields. It is imperative that these practices tested in small plots now be demonstrated in commercial applications to conserve groundwater resources and maintain agricultural sustainability needed to feed China's increasing population.