- Author: Lynn Wunderlich
California Dept. of Water Resources climatologist Michael Anderson kicked off the meeting by attempting to answer the question: "Is the Drought over in California?" The answer is "no", since, even with the rainfall we've received so far, we are not yet seeing near-average run-off accumulating in our reservoirs. This is the result of 4 years of drought and what it takes to actually refill soil profiles enough to accumulate run-off. Michael expects the current El Nino to continue to kick in strong, especially in February, with above average precipitation expected. The freezing elevation level is going to be a key component of whether we accumulate enough snowpack to alleviate our drought in 2016.
Amos Naor, a researcher from the Golan Research Institute in Israel, discussed why plant based stress measurements (stem water potential (SWP) measurements obtained with a pressure chamber) are valuable even when we have soil based sensors and ET0 information. His research in apples, nectarine and pear have shown that the pressure chamber measurements are much less variable than those obtained by dendrometers or tensiometers; and SWP measurements respond more quickly to changes in irrigation regimes, giving the user quicker feedback. Soil moisture variability can be quite large, especially in drip irrigated fields. But the pressure chamber measurements are useless, Naor said, without an established threshold for when growers should use the information to irrigate-this is the key and one I hope to work with foothill grape growers to establish for their blocks. Naor also found that apple crop load can also effect stem water potential measurements-the higher the crop load, the more stressed. I'm uncertain if research has shown this is also true for grapes.
Ken Shackel, UC Davis Plant Science professor and recognized "father" of SWP measurements, described how much
Several speakers addressed irrigation water quality, especially with regards to salinity, an issue that, thankfully, foothill growers don't have to deal with. A number of techniques and models used to estimate and measure soil properties affecting soil water infiltration were discussed. The Israelis have found treated wastewater a valuable and effective water resource, although long term use of wastewater presents challenges due to soil degradation.
The meeting concluded with several grower panels, organized by commodity. Susan Farrington, of Villa Toscano winery and vineyard located in Amador County, accepted my invitation to participate in the wine and table grape grower panel. Susan and her team have experimented this past year with using the pressure chamber, and also use neutron probe soil moisture measurements to make irrigation decisions. Like many foothill growers, they are plagued by problems of iron in their water. After years of sending crews in to change drippers, Villa Toscano is installing a chemical injection system to help keep the iron in solution and hopefully improve their irrigation system's distribution uniformity. Irrigation system distribution uniformity is critical for irrigation efficiency, and is a topic we will revisit in the future. Stay tuned!