CHARACTERIZATION OF WATER-USE BY SULTANA GRAPEVINES (VITIS-VINIFERA L) ON THEIR OWN ROOTS OR ON RAMSEY ROOTSTOCK DRIP IRRIGATED WITH WATER OF DIFFERENT SALINITIES

Seasonal evapotranspiration (ET) was determined for Sultana grapevines grown on their own roots (Own-rooted) or grafted onto Ramsey rootstoc k (Grafted), and irrigated with water of three salinity levels - low - 1 (0.4 dS m(-1)), medium(1.8 dS m(-1)) and high (3.6 dS m(-1)) - durin g the 1994/1995 growing season in south-eastern Australia. Transpirati on (T) was determined from sap flux, soil evaporation (E(s)) with a mo del, and soil water (S) with a neutron probe. Total ET for the season was similar for both Own-rooted and Grafted, averaging 382 mm. However , Grafted partitioned a mean of 193.5 mm (50.84b) of the ET through T compared to 146.7 mm (38.4%) by Own-rooted. Daily rates of T were gene rally low and attained peaks of 1.2 mm (9.9 1 per vine) for Grafted an d 0.9 mm (7.5 1) for Own-rooted in late November, and changed very lit tle until after harvest in February. In contrast to T,the E, rate was consistently higher for Own-rooted than for Grafted from November onwa rds, and at the end of the season totalled 237 mm for Own-rooted compa red to 187 mm for Grafted. Differences between Own-rooted and Grafted in their partitioning of ET into T and E(s) were associated with their canopy development. Grafted had a higher rate of canopy development t han Own-rooted, and in mid-season, the former intercepted about 50% mo re incident radiation than Own-rooted. The crop factors, i. e. ratio o f water use to evaporative demand, based on ET were similar for both v ine types with an average seasonal value of 0.25, but when based on T were 0.12 for Grafted and 0.10 for Own-rooted. The ratio of fresh frui t weight to total water used at harvest, i.e. crop water use efficienc y (CWUE), based on ET, had a mean of 86 kg mm(-1) ha(-1) for Grafted a nd 43 kg mm(-1) ha(-1) for Own-rooted, and when based on T, was 165 an d 115 kg mm(-1) ha(-1), respectively; how ever, supplementary data obt ained during the 1993/1994 season, indicated a CWUE based on T of 294 and 266 kg mm(-1) ha(-1) for Grafted and Own-rooted, respectively. Sal inity did not have significant effects on canopy development and water use for most of the 1994/1995 growing season. The study shows ET and crop factors for the drip-irrigated grapevines to be much lower than p reviously reported for this district.