Pacific Southwest

Title: Using midday stem water potential to assess irrigation needs of landscape valley oaks

Author: Shackel, Ken; Gross, Rob

Date: 2002

Source: In: Standiford, Richard B., et al, tech. editor. Proceedings of the Fifth Symposium on Oak Woodlands: Oaks in California's Challenging Landscape. Gen. Tech. Rep. PSW-GTR-184, Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture: 397-402

Station ID: GTR-PSW-184

Description: In a number of deciduous tree crops a reliable pressure chamber measurement of water stress (midday stem water potential or SWP) has been recently developed and found to be closely related to both irrigation regime and tree physiological responses to stress. A standard pressure chamber is used for the measurement of SWP, but prior to sampling, the leaf is enclosed in a reflective plastic bag and allowed to equilibrate with the water potential in the stem at the point of leaf attachment. In this study, measurements were made on valley oak trees under a variety of landscape conditions in Napa and Sonoma Counties, CA. Measurements on leaves that were only allowed to equilibrate for relatively short times (10 to 15 minutes) were compared to the SWP as measured by adjacent leaves that were allowed to equilibrate for over 1h. As found in other tree species, a 10- to 15-minute covering period appears sufficient in valley oaks for interior canopy shaded leaves to equilibrate with SWP. Using SWP in valley oaks that were nearby construction sites or agricultural land preparation, we confirmed that water stress was associated with root damage caused by these activities. SWP was also sensitive enough to follow the development of and the recovery from water stress over a number of irrigation cycles in an individual tree. We believe that SWP will be a valuable tool to determine the water needs of landscape valley oaks, particularly those with damaged root systems, while avoiding the potential for root disease development due to over-irrigation.

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Citation

Shackel, Ken; Gross, Rob  2002.  Using midday stem water potential to assess irrigation needs of landscape valley oaks.   In: Standiford, Richard B., et al, tech. editor. Proceedings of the Fifth Symposium on Oak Woodlands: Oaks in California's Challenging Landscape. Gen. Tech. Rep. PSW-GTR-184, Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture: 397-402.