The ridge and furrow farming of rainfall concentration (RC) system is being promoted to increase water availability to crops for improving and stabilizing agricultural production in the semiarid Loess region of northwest China. In the system, plastic-covered ridges serve as rainfall harvesting zones and furrows serve as planting zones. In recent years, however, the current RC practices are still confined to rural family units for very limited supplemental irrigation purposes. To adopt this system for large-scale use in the semiarid region and bring it into full play, it is necessary to test the befitting rainfall range for RC fanning. A field study (using corn as an indicator crop) combined with rainfall simulation was designed to determine the effects of RC practices on soil water content, crop yield and water use efficiency (WUE) under three rainfall levels (230 mm, 340 mm and 440 mm) during the growing seasons of 2006 and 2007. The results indicated that with the rainfalls ranging within 230-440 mm, RC system can increase soil water content in 0-100 cm and temperature conditions in the topsoil (0-10 cm) in furrows by 5-12% and 0.7-1 degrees C, respectively. The corn seedlings emerged 1-2 days earlier, the developmental stages generally occurred earlier, and the plant height and total dry matter all significantly increased (P < 0.05). In 2006, compared to conventional flat (CF) practice, the grain yield and WUE in the RC system increased by 75.4% and 73.3%, respectively at 230 mm rainfall, and by 36.7% and 40.2%, respectively at 340 mm rainfall, but there was no significant difference between the RC440 and CF440 patterns. In 2007, the grain yield and WUE were 82.8% and 77.41%, respectively higher in the RC230 Plots than in the CF230 plots, 43.4% and 43.1%, respectively higher in the RC340 plots than in the CF340 plots, and 11.2% and 9.5%, respectively higher in the RC440 plots than in the CF440 plots. Combining yield and WUE, it could be concluded that the optimal rainfall upper limit for RC system is below 440 mm rainfall in the experiment. In the case of corn, the adoption of RC practice in the 230-440-mm rainfall area will make the system more attractive during the whole growth period and offer a sound opportunity for sustainable fanning under semiarid climate. (C) 2008 Elsevier B.V. All rights reserved.
