Among the treatments, WUE was lowest for conventional ridge planting (treatment 7). The second lowest WUE was for the flat gravel–sand mulched field or RFRHS with no-plastic-covered. In general, WUE was relatively high for all RFRHS treatments with plastic-film mulching. The WUE was the highest for the RFRHS with sand mulched furrow plus plastic film whole mulch and the ratio 5:3 of ridge: furrow (treatment 4), and it was significantly higher than the conventional ridge planting and flat gravel–sand mulched field and RFRHS with no plastic covered ridge ( treatment 5). In general, WUE was greatly improved when ridges were plastic mulched. For the gravel–sand mulched field (treatment 1 vs. 8), irrigation remarkably increased WUE in the dry year of 2009. However, WUE was decreased in the wet year of 2007 and had no effect on the WUE value in 2008 with a medium rainfall. This indicated that precipitation had a strong effect on WUE of gravel–sand mulched field.