Abstract: The experiment was conducted to explore the effectiveness of harvested rainwater for supplemental irrigation on watermelon in gravel and plastic mulched field in Gansu,China.The results indicated that in watermelon growing period,soil water content(SWC) of all treatments tended to decrease with fluctuating;theSWC of 0~120 cm decreased by 2.59%~4.13%,the more irrigation amount,the less the SWC decreased.The total water consumption was smaller than that of the other field crops.The water consumptions of various treatments varied from 175.9 mm to 218.9 mm;the water consumption increased with irrigation amount increasing.The yields of various treatments were significantly different;the yield,average fruit weight and the number of fruit increased with the irrigation quantities.Besides,the irrigation quantity had influence on the soluble carbohydrate content of watermelon;when the irrigation quantity was less than 45 mm,the difference of the soluble carbohydrate content was little;but when the irrigation quantity was 67.5 mm,the soluble carbohydrate content decreased by 4.4%.Proper irrigation can promote water use efficiency(WUE) of watermelon;the treatment of 67.5 mm by drip-irrigation had the highest WUE,the WUE was 267.2 kg·hm^-2·mm^-1,which was 17.0% more than that of the no supplemental irrigation.However,with supplemental irrigation quantity increased,water irrigation efficiency and economic benefit of supplemental irrigation decreased.Proper supplemental irrigation can increase yield and WUE,and improve quality.The results demonstrated that harvested rainwater for supplemental irrigation on watermelon in gravel-mulched field was an economic and high-effective way of rainwater utilization;the best irrigation quantity is about 45 mm.

Key words: gravel-mulched field, watermelon, harvested rainwater, drip irrigation