Effect of irrigation rate on yield of drip-irrigated seedless watermelon in a humid region

Seedless watermelon can be a profitable crop in humid regions such as the Delmarva Peninsula in the Mid-Atlantic region of the USA. Production using drip irrigation under plastic mulch is increasingly common but, although this is potentially an efficient production system, it is also complex in terms of irrigation scheduling. Experiments were conducted in 2004, 2005 and 2006 in Georgetown, Delaware to measure the effect of irrigation rate on yield of seedless watermelon grown with drip irrigation under plastic mulch. Relative irrigation rates were used to provide water amounts that ranged from low to high. The irrigation rates in all years included 50%, 100% and 150% of nominal crop water use, with additional rates of 0% and 250% in 2005 and 2006. Data from a nearby weather station were used to estimate reference evapotranspiration. Volumetric soil water content in the 50%, 100% and 150% treatments was measured in the center of each mulched bed using multi-sensor capacitance probes with sensors at depths of 10 cm, 20 cm, 30 cm, 50 cm and 70 cm. Yield of seedless melons per unit area of land ranged from about 55-95 tonnes/ha, depending on the year and the irrigation rate, but within each year the yield differences due to the irrigation rate were not significant (p = 0.10) despite the large range in rate. Differences in quality, as measured by sugar content and the incidence of hollow heart, was also not significant. This lack of response to irrigation may be due to the ability of the root system to use infiltrated rainwater from outside the mulched bed. Growers in the region tend to apply more water than may be required as a form of risk avoidance. This study indicates that irrigation amounts could likely be reduced without having an adverse effect on yield.