Improving Grape and Wine Quality in the San Joaquin Valley

Three irrigation (-1.1, -1.3 or -1.5MPa) and two pruning (hand pruned (HP) or machine pruned (MP)) treatments were applied to approximately 10 acres of a commercial Syrah vineyard near Fresno CA. Each treatment was replicated five times. The primary focus of this project is to use irrigation management early in the season to control vegetative growth and berry size at the different water potential targets. Following the achievement of these water potentials, the goal is to supply sufficient irrigation to bring the soil moisture to 70-80%of field capacity and meet the evapotranspiration demands of the vines.

Data was collected to verify treatments effects on vine growth, water relations, soil
moisture levels, fruit development, fruit quality and wine quality. Soil moisture
measurements on April 21st indicated that despite an attempt to achieve uniform
conditions at the beginning of the season, there was a maximum difference of
approximately 0.4 acre-inch per foot between the MP -1.3MPa (1.8 ac-in/ft) and the HP –
1.3MPa (2.2 ac-in/ft) for the top 3 feet of soil. Field capacity is estimated at 2.47 ac-in/ft.
Despite these initial differences, irrigation treatments were achieved early in the season,
with anticipated effects on fruit size and development. However, the ability to maintain
soil moisture levels between 70 and 80%of field capacity through to harvest was
complicated by apparent differences in crop coefficients between treatments and control
of individual irrigation lines to achieve these differences. These differences were realized
when equal amounts of irrigation applied to all treatments typically showed greater
increases in soil moisture for -1.3 and -1.5 MPa treatments compared to -1.1 MPa

Data indicate MP vines had fewer berries per cluster, smaller berry size, more clusters per
vine than HP vines. These results reflect the combined effects of irrigation and pruning.
Harvest occurred on August 20, 2004 a full month ahead of the 2003 harvest. Brix levels
were generally similar regardless of treatment and ranged from 23.9 to 25.3, with the
greatest differences between the treatment extremes (HP -1.1 vs MP -1.5). Yield for HP
vines were lower than the corresponding MP vines at the same irrigation level. Yields for
HP vines ranged from 4.5 to 7.6 tons/acre, while yields for MP vines ranged from 5.6 to
9.0 tons/acre. In both HP and MP vines, the clear trend was for higher yields as the
amount of irrigation was increased and stress was lower. Reduced stress resulted in
larger berries and contributed significantly to yield. Within the MP vines, vines that
received less water early in the season (-1.5 MPa) had higher Brix at harvest. MP vines
also had fruit with lower pH, higher titratable acidity and color intensity than HP vines
with the same irrigation. Fruit quality analysis was undertaken with a taste panel.
Statistical analysis will be available in the near future. WineScan analysis indicated an
increase in polyphenols as irrigation declined. The continuing goal of this research
project is to determine the best combination of these irrigation and pruning practices to
achieve better quality in an economically viable manner.

After some difficulty in completing the malolactic fermentation of the 2003 wines, they
are now in bottle and taste panel work is underway. These wines will be used in a
discussion of Syrah grape production at the Central Coast Grape and Wine Symposium in
February 2005. These wines will also be analyzed by Dr. Douglas Adams laboratory for
total anthocyanin and phenols.

Wines made from the 2004 growing season are being finished and will be used to do taste
panel analysis and for grower demonstrations of the effects of pruning and irrigation on
grape and wine quality. Our results are consistent with those reported from other wine
regions and indicate that timing of irrigation has a significant influence on fruit and
therefore wine quality. Our results are consistent with those reported from other wine
regions and indicate that timing of irrigation has a significant influence on fruit and
therefore wine quality.