The effect of supplemental irrigation on watermelon (Citrullus lanatus) production in gravel and sand mulched fields in the Loess Plateau of northwest China

Abstract Trials were conducted to examine the effects and economic feasibility of supplemental drip irrigation on watermelon ( Citrullus lanatus ) production in fields with and without surface mulch consisting of a mixture of gravel and sand in the Loess Plateau of northwest China in 2001 and 2002.The trial involved four levels of drip irrigation: 0, 23, 45 and 68 mm of water to both mulched and non-mulched fields (control). Both treatments were randomized with four replications. There was a significant difference in rainfall amounts between the two experimental years. Rainfall during the watermelon growth period was 126 mm in 2001 and 223 mm in 2002. In 2001, 45 mm of irrigation increased yields by about 36% and 68 mm increased yields by about 46%. Drip-irrigation, with 68 mm had the highest water use efficiency (WUE), 24.7 kg m −3 , which was 29.3% more than the non-irrigated treatments. In the wet year, 2002, supplemental irrigation decreased WUE for the mulched fields but did not significantly increase yields. However it did increase yields in the non-mulched fields: 23, 45, and 68 mm of irrigation increased yields by 21, 26 and 38%, respectively. In 2002, the average yield increase for the mulched treatments as compared to the non-mulched treatments was 25.4%, or 11,400 kg ha −1 , with a corresponding average increase in WUE of 25.3%, or 3.7 kg m −3 . There were no significant differences in the soluble solid content of the melons among the irrigation treatments for the mulched treatments. However, for the control treatments, the soluble solid content of the 45 and 68 mm irrigation treatments was significantly lower than for the 0 and 23 mm irrigation treatments. The net seasonal income was estimated to be highest at US$ 6012 ha −1 for the 0 mm irrigation treatment in mulched fields in 2002, the wet year, followed by US$ 4938 ha −1 for the mulched with 68 mm of irrigation in 2001, the dry year. The net profit per mm of water used was the highest (US$ 20.8 mm −1 ) for the mulched, 68 mm irrigation treatment in 2001. Supplemental drip irrigation of mulched fields in dry year definitely increases watermelon yields.