Effects of irrigation management and watertable depth on growth and yield of field-grown Sultana grapevines in south eastern Australia

The influence of irrigation amount and frequency of application on growth and yield of Sultana grapevines was studied in a field trial carried out over four years in the Murray Valley irrigation area of Australia. Treatments included low (280 mm of irrigation and rainfall), medium (780 mm) and high (1300 mm) application amounts, each with frequencies of 1, 2 and 4-weekly. Despite artificial drainage, there was a watertable of variable depth: its effect was evaluated by grouping plots into those with shallow (<2.2 m depth) or deep (>2.2 m depth) watertables. Treatments were applied to grapevines with Sultana scions grafted to Ramsey rootstocks and own-rooted Sultana vines. Yields from vines grafted to Ramsey were largely unchanged by irrigation treatments even where shallow watertables resulted in high soil salinities (ECe > 3.0 dS m−1), probably because of the capacity of Ramsey rootstock to exclude chloride ions. For vines on their own roots, there were interactions between irrigation frequency and watertable depth for soil salinity and yield, with the fortnightly frequency offering the best compromise where there was a shallow watertable. The response to irrigation amount also depended on watertable depth; the low amount reduced yield relative to that in the medium and high amounts in areas where the watertable was deep but not in areas where it was shallow. Yield in the medium and high amounts tended to be lower in areas where the water table was shallow compared with areas where it was deep. The results suggest that where shallow watertables are present irrigation management should be modified for both own-rooted and Ramsey grafted Sultanas to apply no more than moderate amounts of irrigation and preferably at not less than fortnightly intervals.