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November 2015 WINES&VINES 29 GROUNDED GRAPEGROWING Traditional tools for irrigation monitoring While there are useful devices to assist in measuring soil moisture and plant stress, many have limi- tations, and typically most grow- ers aren't patient enough to take the data, process the information and make adjustments to their ir- rigation schedules on their own. Most of these devices are used by irrigation consultants who do weekly readings and advise grow- ers how to schedule their irriga- tions. Here is a quick review: Gypsum blocks, water marks These and other soil sensors are fairly simple, containing an elec- trode that can be used to measure the electrical resistance that oc- curs as the soil dries and water is released by evaporation. They must be buried in the soil at dif- ferent depths, energized and data recorded regularly. They sense an area around them of 4 inches, so you have to choose an area that you believe to be typical of the vineyard, or set up multiple spots. They give good information for the price (each spot that you are monitoring is going to cost about $100 for sensors, and another $300 for a meter to read the sen- sors.) There is also the possibility of connecting them to transmit data by cell phone, but this starts to get expensive fairly quickly. Pressure bombs Used to assess vine moisture sta- tus, these devices apply com- pressed gas to a leaf inside a sealed chamber with an opening that uses a rubber grommet to compress and seal the chamber around an exposed petiole on the outside of the chamber. The cham- ber is pressurized until sap is pushed through the cut end of the exposed petiole. At that point, a pressure gauge indicates the ten- sion with which the leaf is holding onto its sap. The devices are ex- pensive (around $3,000), slow to use, clunky to haul around and need to be refilled with very high- pressure gas. This remains a fan- tastic research tool, but most growers find it too cumbersome to own and operate. Most consul- tants use it to determine irrigation thresholds for regulated deficit irrigation programs. Capacitance or C-probes A C-probe measures the volume of soil moisture by using capacitance sensors. Capacitance is the ability of an object to hold an electrical charge. C-probes are very accurate. The sensors are mounted at differ- ent distances on a column that is placed into a PVC access tube in the ground. These are often add-on devices to weather stations and tend to be expensive ($2,000- $3,000, depending on the number of sensors). Typically they have to be calibrated and do not give direct soil moisture information in their displays. They only sample a small area in the vineyard. Neutron probes These devices can only be used by licensed technicians since they use a radioactive source in the probe. The probe is in a shielded con- tainer for transport that is placed above an aluminum tube in the field and then lowered to different depths to take readings. It is also a clunky device. While the infor- mation is extremely accurate, it requires software to graph data and usually a consultant to make irrigation recommendations. Conclusions Technology is constantly giving growers new tools to assist them in making management decisions. It is important not to get bedaz- zled by technology—the best as- sessment and management tool available resides between your ears. As a vineyard manager, good observations, careful analysis and timely follow up are not likely to be surpassed by technology alone any time soon. Yet having helpful information at your fingertips can only improve your knowledge base and allow you manage your vines with more precision. Glenn McGourty is the University of Cali- fornia Cooperative Extension winegrow- ing and plant science advisor for Lake and Mendocino counties. He tends a 1-acre vineyard of the aromatic Italian wine grape variety Arneis on his property along the Russian River near Ukiah, Calif. Quality made in Germany 29.09.15 12:13