Performance of double-cropped winter wheat-summer maize under minimum irrigation in the North China Plain

The double cropping of winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.) in the North China Plain (NCP) requires intensive irrigation that results in rapidly depleting aquifers and threatens the sustainable agricultural development in the region. This study investigated the possibility of growing winter wheat and maize with minimum irrigation (MI) by bringing soil moisture in the top root zone to field capacity at sowing with no further irrigation afterwards. Results over 8 yr (1997-2005) showed that grain yield of winter wheat was over 5000 kg ha(-1) and maize was over 6000 kg ha-1 in most of the seasons under MI. The average yield was decreased by 14% for winter wheat and 13% for maize compared with the fully irrigated treatment (FI). Water use efficiency (WUE) under MI was increased by 15% for winter wheat and 10% for maize compared with that under FI. Average seasonal evapotranspiration (ET) was 335 mm under MI and 447 non under FI for winter wheat, and 319 mm and 403 mm for maize, respectively. The annual irrigation requirement of MI was only half that of FI. Yield reduction in MI was negatively related to seasonal rainfall (significant at P < 0.05). The success of MI depended on the deeper root system of winter wheat using soil moisture that accumulated below the shallower rooted maize over the summer rainfall season. The results showed that an MI strategy that would be simple to implement for farmers would contribute significantly to the sustainability of the groundwater resource.