Calculating Stem Water Potential
To find baseline stem water potential (i.e., what water potential to expect under wet soil conditions for your date and time of sampling), select the CIMIS weather station closest to your orchard, or with the most similar climatic conditions. Use the map on the right to help select the most appropriate station, then select the station, date, and approximate time of your pressure chamber readings and press ‘update.’ Temperature, relative humidity, and baseline water potential values for almond, prune, walnut, and grape (both SWP and LWP) will be displayed.
The baseline value provided on this website indicates the expected stem water potential of a tree if soil water had not been limiting. This baseline value should be compared to stem water potential measurements made in your orchard to determine whether irrigation is needed.
After selecting the appropriate station enter the date (must be within one week of the current date) and the time of pressure chamber readings. Pacific standard time is used, subtract one hour from daylight savings time.