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June 2015 P R A C T I C A L W I N E R Y & V I N E YA R D 63 G R A P E G R O W I N G G rapegrowers are encouraged to use a combination of soil, plant and weather data when determining the length and fre- quency of irrigation events in vineyards. The most common questions that grow- ers ask about vineyard irrigation are: How often should the vines be watered, and how much water should be applied per irrigation? Estimation of daily evapotranspira- tion can tell a grower roughly how much water is removed from the soil, and it is the principal means by which grow- ers can determine the amount of water to apply to a vineyard block. Plant data (such as leaf or stem water potential determined by means of a pressure chamber) is often used to determine how vines are responding to the amount and frequency of water applied. For example, if a grower wishes to strategically apply less water than the amount lost to evapotranspiration (a def- icit irrigation strategy), a plant water sta- tus measurement can be used to indicate the degree of water stress the vines are experiencing. Why measure soil moisture? Soil moisture sensors are a useful tool for assisting with vineyard irrigation scheduling. For example, water status of the soil can be measured during the winter to deter- mine if winter rainfall is reaching the effective rooting area of vines. Soil mois- ture sensors are also helpful to determine the irrigation time required to replenish water to a desired rooting depth. The data provided by soil sensors can help growers to understand how water moves in soil and the areas where roots are most actively taking up water, poten- Fritz Westover, Viticulturist, technical program manager, Vineyard Team BY Where to install soil moisture sensors Figure 1. Numerous soil moisture sensors are available for use in vineyards. Examples of different sensors include: Watermark Matric Potential Sensors (top left), AquaCheck Capacitance Probe Sensors (top right), and Decagon capacitance sensors (bottom). How and where you install the sensors is likely more important than the type of sensor chosen. KEY CONCEPTS • Soil sensors must be installed in the location that best represents a vine- yard irrigation block. • Mapping soil (pre-and post-plant- ing) and vine vigor patterns (post- planting) provides useful information for selecting sensor installation sites. • A strategy must be developed to evaluate the soil in a block to verify placement of sensors in a representa- tive soil profile. BLOCK G 7.74 ac Figure 2. This normalized difference vegetative index (NDVI) map of an existing vineyard shows areas of high vigor in dark green and those of progressively lower vigor in yellow, orange and red. A combination of deeper clay soil and a drainage pathway of a swale to the west side of block G are the likely reasons for higher vigor in that area (darker green color). Soil sensors should not be placed in these areas if the data is to be representative of the majority of the block.