Deficit Irrigation

What Is Deficit Irrigation?

The amount of moisture that plants are capable of drawing from the soil is dependent on various factors. Environmental factors such as temperature, relative humidity and wind velocity as well as the growth stage of the plant, determine how much water can be used at a given time. The technical term for this plant water use is evapotranspiration or ET. When a plant's evapotranspiration rate exceeds the amount of moisture available to it in the soil, it experiences a soil moisture deficit which results in a certain amount of plant stress.

Most vineyards in California are irrigated at some point during the season in order to minimize soil moisture-induced stress caused by a lack of rainfall. Many growers have noticed that limiting irrigation at certain stages of fruit developement has a beneficial effect on the level of sugar producton in their crop. This deliberate reduction in irrigation in order to create a certain level of plant stress is known as deficit irrigation.

Advantages

The possible advantages of using a deficit irrigation strategy for irrigating wine grapes are numerous. By limiting a vine's ability to absorb moisture at various stages of its growth cycle, it is possible to control certain canopy and fruit characteristics.

For example, stressing the vine early in the season while the canopy is expanding can restrict excessive vegetative growth. Canopy area reduction can reduce the undesirable vegetable taste in the wine, allow better light penetration in the fruit zone and better air circulation. More light in fruit zone near the end of the ripening period has the effect of increasing phenolic development in the fruit. Phenolic compounds are the source of the color, flavor and aroma characteristics and can mean the difference between a mediocre and a world class wine. Better air circulation can reduce disease infestations and allow for more even ripening in the fruit clusters.

Early season irrigation deficits can also result in smaller berry size within the cluster. Smaller berries mean a larger skin-to-juice ratio resulting in more color intensity in red varietals, higher levels of sugar concentration, less bunch rot and more uniform ripening within the cluster.

Other advantages relate to how growers were irrigating prior to implementing a deficit irrigation strategy. If they were irrigating their vines at full potential previously, they not only could increase thier quality, but could experience a reduction in irrigation costs since deficit irrigation applies only a fraction of a grape vine's full water potential. If they were underirrigating previously, then a yield increase could be possibile.

If you know how much irrigation water you applied to your vineyard last season and would like to compare it to the amount you would have used with our strategy, then use our free Irrigation Calculator.