EFFECT OF IRRIGATION TO WINTER WHEAT ON THE SOIL MOISTURE, EVAPOTRANSPIRATION, AND WATER USE EFFICIENCY OF SUMMER MAIZE IN NORTH CHINA.

A double-cropping system such as that of winter wheat and summer maize in north China requires irrigation to achieve production goals. The soil during the seeding stage of summer maize is usually dry. For summer maize, soil moisture before sowing (SMBS) is important for seedling growth, yield, and water use. Our objective was to investigate the effects of applying different irrigation schedules to winter wheat on the SMBS, yield, and water use efficiency (WUE) of summer maize. Field experiments involving winter wheat with 0, 1, 2, and 3 irrigation applications (T0, T1, T2, and T3, respectively) were conducted in a dry year (2002), moderate year (2003), and humid year (2005). Irrigation of winter wheat increased the average SMBS of summer maize in the 1.2 m soil profiles to 17.7, 57.3, and 79.6 mm in T1, T2, and T3, respectively. Differences in the soil moisture content among the treatments were significant in the late growing season of summer maize in the dry and moderate years but not in the humid year. In 2005, maize yields among the treatments were not significantly different as compared to those in T0; the yields increased from 22.1% to 56.0% in 2002 and from 1.9% to 11.4% in 2003. Compared to T0, the WUE of summer maize increased by 15.3%, 23.6%, and 24. 7% in T1, T2, and T3, respectively, in 2002 and by 0.01%, 3.4%, and 5.4% in 2003; however, it decreased by 2.4%, 5.6%, and 12.4%, respectively, in 2005. Considering the combined WUE of winter wheat and summer maize, there was no significant difference between T2 and T3 (LSD, P < 0.05). These results suggest that winter wheat should be irrigated at the jointing and heading stages to achieve reasonable grain yield and WUE for both the crops. [ABSTRACT FROM AUTHOR]