The Response of Three Year-old Thompson Seedless Grapevines to Drip and Furrow Irrigation in the San Joaquin Valley.

The response of three year-old grapevines (Vitis vinifera L. cv. Thompson Seedless) to furrow and drip irrigation was quantified in terms of water status, shoot growth, WUE, dry weight and nitrogen partitioning, and root distribution. Drip irrigation was applied daily according to best estimates of vine ET while furrow irrigations were applied when 50% of the plant available soil water content had been depleted. Water distribution within the soil profile was measured for both treatments using the neutron probe. Drip and furrow irrigated vines showed similar water status and shoot growth patterns throughout the season. Dry weight partitioning was not significantly different between treatments but root mass was somewhat larger in furrow than in drip vines. There was a confined and shallow root system of drip vines that coincided with the soil wetted zone around the emitter discharge. In contrast, furrow irrigated vines showed a deep and widespread root system. Nitrogen concentrations of the fruit and roots were significantly lower for the drip irrigated vines when compared to the furrow treatment. Differences between water applied and soil water content three days after furrow irrigation indicated large water losses by evaporation during that time frame. Similar WUEs of applied water were obtained for both treatments. The potential for furrow irrigated vines compared with drip irrigated vines to utilize water previously stored is discussed. The data indicate that drip irrigation would increase the potential for control of vine growth by making vines more dependent on irrigation and N fertilization than furrow irrigation due to its effect on confining the root system. Water consumption of drip irrigated vines was 36% of the vineyard irrigation deliveries for this area of the San Joaquin Valley. Water consumption of the furrow irrigated vines was 12.5% more than the drip irrigated vines. In either case, these results show a potential for significant water savings in San Joaquin Valley vineyards with better irrigation management by grape growers.