A comparative study of young ‘Thompson Seedless’ grapevines under drip and furrow irrigation. I. Root and soil water distributions

Soilwater distribution, soilwater extraction, and root distributions were determined for young grapevines (Vitis vinifera L. cultivar ‘Thompson Seedless’) grown under drip and furrow irrigation near Fresno, CA, USA. Soilwater content and extraction was determined to a depth of 0.9 m by neutron scattering from an array of nine access tubes installed throughout one-quarter of the soil volume available to each vine. Root distribution was determined from root intersections with vertical planes established parallel and perpendicular to the vine row. Drip irrigation was applied daily according to estimated evapotranspiration, and furrow irrigation was managed according to 50% depletion of the plant available soil water. Drip and furrow irrigated vines showed similar water status and shoot growth patterns. There was a confined soil wetted zone beneath the emitter discharge that largely coincided with a confined and shallow root system of drip irrigated vines. In contrast, furrow irrigated vines had a deeper and more widespread root system. Differences between water applied and soilwater content 3 days after irrigation suggested large water losses by evaporation during that period for furrow irrigated vines. Consumptive use of furrow irrigated vines was 12.5% greater than drip irrigated vines, but similar irrigation efficiencies were obtained for both irrigation systems when soilwater status was carefully monitored. Water applications for both irrigation systems were less than 50% of the longterm mean for irrigation deliveries to farms in the area. Thus, the results indicate that a significant potential for water savings exists in the San Joaquin Valley by means of irrigation management. It is concluded that relatively high and similar irrigation efficiency can be obtained with both drip and furrow irrigation of young grapevines in arid and semiarid regions when careful management is used.