Dry farmed vineyards in Murcia, (Spain), Bordeaux, and Napa Valley, show large differences in vine performance resulting from different climates, specifically rainfall during the season, and different soil depths and textures. These vineyards illustrate that, beyond the fact that no irrigation water was applied, there are no necessary commonalities in vine performance in dry farmed vineyards.
After climate and soil, planting density and rootstock are probably the two most important influences on vine performance. Research shows that lower planting densities have more vegetative growth per vine but less vegetative growth per unit land area. Consequently, in a dry farmed vineyard, a lower planting density has more soil moisture per unit of vegetative growth. This would be an advantage at locations where there are low amounts of rainfall during the growing season and the soil profile holds most of the water available to the vines.
Using a drought tolerant rootstock is important in many dry farmed vineyards. There is no single way to measure drought tolerance; researchers have used measurements of vegetative growth, vine water status, reproductive growth as well as visual health to assess the drought tolerance of different rootstocks. All of these approaches were used to examine the drought tolerance of four rootstocks (110R, 1103P, 140Ru and 5C) in a dry farmed trial at the Oakville Experimental Vineyards. The results of the trial gave a mixed picture of the rootstocks’ drought tolerance, with some rootstocks performing better in some measurements and less well in other measurements. Weighing all the measurements together it was concluded that 110R & 140Ru were more drought tolerant than 1103P and 5C.
Some potential benefits of dry farming vineyards:
- Grow grapes at locations with no available water, for example areas in Spain, or the coastal hilltops in Sonoma.
- Conserves water, using less water for irrigation will leave more for other uses.
- Easier than answering the question “When and how much…?”, imagine never needing a pressure bomb, a neutron probe or the ET equation.
- Lower farming costs, no need for reservoirs, wells, pumps and irrigation systems. Increase crop value, if dry farming is like “old vines”, it may be something that appeals to winemakers or consumers.
Some potential liabilities of dry farming vineyards:
- Temperature spikes, it may be desirable to apply water before heat waves to avoid leaf loss or steep increases in oBrix values.
- Variability within vineyard soils, not irrigating precludes the ability to differentially irrigate parts of vineyard to compensate for differences in soil depth and texture.
- Year to year variability, there can be differences from year to year in the amounts of water available in the soil profile and from rainfall during the growing season.
- Eliminate the ability to fertigate; nitrogen and potassium applications during the growing season are common in commercial vineyards but are not an option in a dry farmed vineyard
- Reduced nutrient availability, minerals diffuse in the soil water solution, lower soil moisture may reduce nutrient availability.
- Limits choices of spacing, rootstock and trellising system, high-density plantings, low-vigor rootstocks and trellising systems requiring large vine size may be less appropriate in dry farmed vineyards.
- Lower yields, are likely.
In conclusion, it would be possible to grow grapes at most sites without irrigation. Dry farming does not guarantee an economically sustainable yield or improved fruit quality. It is fortunate when a particular vineyard produces desirable amounts of vegetative growth and yield, and also fruit quality without irrigation, but this is probably not true for many vineyard sites.