A COMPARATIVE-STUDY OF YOUNG THOMPSON-SEEDLESS GRAPEVINES UNDER DRIP AND FURROW IRRIGATION .1. ROOT AND SOIL-WATER DISTRIBUTIONS

Soilwater distribution, soilwater extraction, and root distributions w ere determined for young grapevines (Vitis vinifera L. cultivar 'Thomp son 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. Roo t distribution was determined from root intersections with vertical pl anes established parallel and perpendicular to the vine row. Drip irri gation was applied daily according to estimated evapotranspiration, an d furrow irrigation was managed according to 50% depletion of the plan t available soil water. Drip and furrow irrigated vines showed similar water status and shoot growth patterns. There was a confined soil wet ted zone beneath the emitter discharge that largely coincided with a c onfined and shallow root system of drip irrigated vines. In contrast, furrow irrigated vines had a deeper and more widespread root system. D ifferences between water applied and soilwater content 3 days after ir rigation suggested large water losses by evaporation during that perio d for furrow irrigated vines. Consumptive use of furrow irrigated vine s 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 delive ries to farms in the area. Thus, the results indicate that a significa nt potential for water savings exists in the San Joaquin Valley by mea ns of irrigation management. It is concluded that relatively high and similar irrigation efficiency can be obtained with both drip and furro w irrigation of young grapevines in arid and semiarid regions when car eful management is used.