Direct root-zone irrigation outperforms surface drip irrigation for grape yield and crop water use efficiency while restricting root growth

Direct root-zone irrigation is a novel subsurface drip irrigation strategy for water conservation. However, a comparison with traditional irrigation methods is lacking to better define the potential advantages of direct rootzone irrigation. A two-year study was conducted to evaluate the performance of Vitis vinifera L. cv. Cabernet Sauvignon under direct root-zone irrigation and surface drip irrigation in a commercial vineyard with loamy sand soil in a semi-arid region of southcentral Washington State, USA. Plant water status, root traits, grape yield, berry morphology and composition, and crop water use efficiency were compared between irrigation methods under three irrigation rates. Compared to surface drip irrigation, direct root-zone irrigation improved grape yield by 9-12% and crop water use efficiency by 9-11% under varied climate conditions with minor effects on berry composition, which could be potentially adjusted by irrigation rate. Moreover, grapevines irrigated through direct root-zone irrigation had 48-67% and 50-54% decrease in root number, respectively, at high and moderate irrigation rates in the upper soil profile (0-60 cm) with a decrease in water stress as revealed by higher midday stem water potential. Irrigation rate was the major factor influencing berry morphology. In fact, reduced irrigation resulted in a decrease in weight, size and number of berries. We conclude that direct root-zone irrigation could be a successful tool for improving yield and crop water use efficiency, potentially encouraging deep rooting to alleviate the water stress in grapevine under seasonal drought, and offering the ability to modify berry morphology and composition by adjusting the amount of water use.