A study was initiated during the 2001-growing season at three different sites to determine the interaction of different irrigation amounts and several canopy management practices on leaf, stem and cluster water relations, berry characteristics and productivity. The irrigation amounts were various fractions of estimated vineyard evapotranspiration (Etc), the specific amounts were agreed upon by each grower/cooperator. The canopy management practices included the use of different trellis systems, vine and row spacings, row direction, cluster exposure and leaf removal. The vineyard sites chosen were in the Napa, Livermore and San Joaquin Valleys. The two cultivars used were Cabernet Sauvignon in Napa and Livermore Valleys and Merlot in Madera County.
At the Napa Valley vineyard site, crop coefficients developed in the 2000-growing season for a lyre and VSP trellis on 9-foot rows and a VSP trellis in a 1 x 1 m planting density appeared appropriate for irrigating those treatments in 2001. Calculated Etc was greatest for the 1 x 1 m planning density followed by the lyre and then the VSP. Berry weights were different among the three-trellis/spacing treatments only when no water was applied. However, there were no significant differences in berry weight among those trellis/density treatments when comparisons were made at each individual irrigation amount (i.e. at 25, 50 and 75%of estimated Etc).
Cluster water potential was highly correlated with leaf water potential on a diurnal and seasonal basis. Water potential of sunlit clusters were more negative (more stress) than shaded clusters at the time of measurement. Cluster water potential was also a function of date, trellis, and irrigation amount. The above data would indicate cluster water relations might also play a role in affecting berry characteristics when canopy management procedures are used to provide more light into the fruiting zone. Further analysis is needed to determine exactly the effect cluster water relations do have on berry characteristics under such conditions. Canopy management and irrigation affected berry characteristics to differing degrees at all three locations. In most instances increased applied water amounts affected berry weight, soluble solids (oBrix) and titratable acidity similarly at all locations and among canopy management treatments. Comparison of the effects of canopy management treatments on berry characteristics could not be made due to the fact that those treatments were not the same at each location. Berry color and several other constituents can be significantly affected by water stress and light. Unfortunately, berry anthocyanins, phenolics and tannins have not been analyzed as of the date this report was written. The response of yields to applied water amounts at all three locations was similar in many respects to those I’ve measured in past studies. In general water application amounts greater than 75%of estimated ETc maximized yields in Madera County and the Livermore Valley. Yields were dependent upon trellis/density treatment used in Napa Valley. The greatest yields at all irrigation treatment amounts at that location was at the 1 x 1 density followed by the lyre trellis.