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66 P R A C T I C A L W I N E R Y & V I N E YA R D June 2015 G R A P E G R O W I N G Note that the soil from the high-vigor area (A) of the vineyard has clay con- tent as deep as 4 feet, whereas the soil core from the top of the hill (D) has heavy clay top soil down to about 2 feet, followed by a sharp transition to loam. The two cores from the center of the block (B, C) are of the most representative soil, having a sandy clay loam top soil, transitioning to clay loam, then loam subsoil. After reviewing soil maps and vine vigor, a strategy should be developed to evaluate soil in the irrigation block, such as digging observation pits in a grid pattern across a block. This extra step will help to verify that the soil sensor placement is in an area that represents the most commonly observed soil profile. Depth of soil sensor placement After determining the most repre- sentative location for placing soil- moisture sensors in an irrigation block, the depth of sensor placement must be considered. Choosing the depth to place individual soil moisture sensors requires careful evaluation of the soil profile. Due to the deep-rooting habit of grapevines, it is common to place sensors at increasing soil depths in order to capture the movement and potential availability of water. When using a probe-type sensor with multiple sensor depths pre-set by the manufacturer, the most important decision is the total length of probe required to reach the desired soil depth. Be sure that the length matches the depth with which you wish to monitor water movement and that the soil depth is adequate for full insertion of the probe. A sensor at or near the bottom of the root zone is suggested to identify deep percolation. Before final installation of soil sensors, observation points can be evaluated in the area immediately surrounding the sen- sor location (Figure 4). Evaluation of a soil profile within 2– 3 feet of a proposed installation site is a helpful practice to make sure you do not install sensors in a disturbed spot. Note, any observation hole dug within a few feet of a sensor site must be carefully back-filled and tamped to pre- vent rainfall or other surface water from influencing sensor readings. Sensor placement relative to emitters and vines The location of soil moisture sensors relative to the vine root system and drip emitters (in irrigated vineyards) will influence the usefulness of the sen- sor readings. If sensors are placed too far from active roots, the effect of water movement in mass flow cannot be captured. Likewise, placement too far from the emitter can lead to overwatering of vines if the sensor is not within the desired wetting pattern of a routine irri- gation set. Most growers will tend to err on placing sensors closer to the emitter (within 4– 6 inches) in order to avoid excess watering. Some trial and error may be necessary to find the best distance from emitters in a particular soil. Soil sensors are most commonly positioned within 18 inches of a vine trunk and in line with trellis and irrigation wires to reduce damage from machinery (Figures 5, 6). Where to avoid placing sensors In general, sensors should not be placed in the following areas of a vineyard: • Areas of excessively high or excessively low vigor that do not represent the majority of the block. • Soils that do not drain well or hold water longer than the majority of the block. • Where soil depth is deeper or shallower than the majority of the block. • Pockets of soil that do not represent the majority of the block (random sand pockets, or hard pan). • Areas in line with surface runoff (bottom of swales) or drain- age channels in a block. • On the border of the vineyard or areas near competing veg- etation. • Areas that receive supplemental shade from structures or trees other than vines or trellis. • Where natural soil structure has been disturbed in the past (backhoe pits, uprooted trees and backfill from erosion). • Areas that may receive significantly more or less irrigation water than the rest of the block (this may be based on evalua- tion of distribution uniformity). • Where vines are not representative of the block (weak vines, vines of different age or rootstock). PWV This text was developed by the Vineyard Team, a nonprofit organi- zation dedicated to promoting sustainable winegrowing since 1994. Materials are based upon work supported by industry contributors and the Natural Resources Conservation Service, U.S. Department of Agriculture, under No. 68-9104-3-177. Any opinions, findings, conclusions or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of the U.S. Department of Agriculture. Author's Note: Additional information on types of soil moisture sensors and tips for installation can be viewed on the Vineyard Team website at: vineyardteam.org/projects/ vineyard-demonstration.php. Bibliography 1. U.S. Department of Agriculture, National Resource Conservation Service - Web Soil Survey: websoilsurvey.sc.egov.USDA.gov/app/homepage.htm. Figure 6. A typical soil moisture sensor installation shows the placement distance about 18 inches from the vine trunk, and 4–6 inches from a drip emitter.