Research helps growers conserve water, improve white wines

Washington State University viticulturists Yun Zhang and Markus Keller are finding ways to conserve water and improve production of white wine grapes by using partial rootzone drying, or PRD.

The technique, developed in Australia, involves applying water only to one part of the vine’s rootzone while letting the other part dry out. The vine is effectively tricked into thinking it is water stressed though it isn’t.

For the last two years, Zhang has been evaluating management strategies growers can use to make sure water is delivered when and where it is most needed while improving the productivity and quality of chardonnay and riesling grapes.

“PRD has the potential to become a useful irrigation tool for white wine grapes,” Zhang said. “Once the threshold to trigger irrigation is set, by tracking the soil moisture changes on both parts of the rootzone, it’s clear whether you should irrigate or not and how much.”

At WSU’s Wine Science Center, enologist Jim Harbertson produces wine from the grapes in the study to see if the differences carry through to the finished product.

In addition to testing different deficit irrigation strategies, Zhang and Keller are assessing three decision aid tools for irrigation scheduling.

The research is conducted in cooperation with Ste. Michelle Wine Estates and funded by the WSDA Specialty Crop Block Grant Program and the Washington Wine Commission.

Zhang and Keller will present on vineyard irrigation management at the Washington Association of Wine Grape Growers meeting Feb. 9-11 in Kennewick, Washington.