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Dr. Larry E. Williams
Professor & Plant Physiologist Department of Viticulture and Enology Agricultural and Environmental Sciences
The major thrust of my research program currently is vineyard irrigation management. I have irrigation experiments established on wine grapes (trials located in Napa, Monterey, San Luis Obispo, and Santa Barbara counties), table grapes (trials located in Fresno and Riverside counties), and raisin grapes (trial located at the Kearney Agricultural Center). The primary objective of these studies is to determine how much water vines will use under non-stressed conditions. The data will be used to determine reliable crop coefficients at the various locations in order to help grape growers schedule irrigations (both timing and amount). Subsequently, I will determine the effect of regulated deficit irrigation (RDI) on vine physiology, growth and fruit yield, and quality. I have also determined the amount of water Thompson Seedless and Chardonnay grapevines require during vineyard establishment. I have developed a model to predict water use of Thompson Seedless grapevines and compared the model output with actual water use, measured with a weighing lysimeter. Modelling efforts for both water use and carbon assimilation are proceeding. Lastly, I had a graduate student studying water relations of native Vitis species grown under soil water deficits. It is anticipated that results from this study may assist grape breeders in developing drought tolerant rootstocks. Results of these studies are currently being published. Many of the cultural practices used in modern viticulture affect the vine's source/sink relationships. While much of the research I conduct is applied, I still am able to collect data more basic in nature, especially in regard to source/sink relationships of field-grown grapevines. Much of the data were collected at the Kearney Agricultural center and represent information never before published. These data have allowed for new interpretations of source/sink relations of field-grown grapevines. This information was recently published.