The objective of this study was to develop alternative deficit irrigation management strategies for wine grapes and to determine the impact of these strategies on water saving, crop yield, fruit composition and plant response.
- The trial was conducted for four years in a 14-year old block of Cabernet Sauvignon in California, on well drained, sandy loam over clay soil;
- The growing season was divided into three periods:
1. Budburst to fruit-set: No irrigation applied
2. Fruit-set to three weeks post fruit-set: 75% of calculated crop water use (ETc) was applied in all treatments
3. Three weeks post fruit-set until harvest: Irrigation resumed when leaf water potential reached -1.2MPa in one of three sustained deficit irrigation (SDI) treatments:
a. LOW 25-35% of ETc
b. MEDIUM 50% of ETc
c. HIGH 65-75% of ETc
- Grapes were harvested at 25°Brix and subsequent analysis done.
- Yields in the MED and HIGH treatments were more than in the LOW treatment.
- There was however no difference in yield between MED and HIGH treatments;
- Berry weight, clusters per vine, cluster weight and yields varied across the years within each treatment with no distinct pattern. This means these variables’ responses were independent of the irrigation management;
- Pruning weights increased as the applied water increased, but there was no difference between MED and HIGH treatments;
- Pruning weights and berry size decreased every year in all treatments;
- Irrigation treatment had no effect on fruit composition variables in a given year. These variables differed between years, due to climate and harvest dates.
Significance of the study:
The MED deficit irrigation strategy led to water savings, while still maintaining yields. This strategy also showed consistent water productivity over the years of the study. Severe reduction in irrigation (as with the LOW treatment) led to severe decreases in yield and is not a sustainable treatment.