California Agriculture

In 1986, two large weighing lysimeters, — one in a peach orchard and the other in a grape vineyard — were constructed at the UC Kearney Research and Extension Center as a joint effort between UC and the U.S. Department of Agriculture’s Water Management Laboratory. Hourly weight changes in the lysimeters have been used to measure the daily and seasonal water use of trees and vines for nearly 20 years. Peaches and grapes exhibit similar seasonal crop-coefficient patterns that start as low as 0.1 in March, increase linearly until early July and then remain constant between 1.1 and 1.2 for the remainder of the season (provided the plants remain disease-, pest- and stress-free). The linear increase phase is proportional to the increase in canopy light-interception and leaf area. These relationships have facilitated modeling to predict crop evapotranspiration under various conditions. The peach lysimeter has also been useful for studying the effects of water stress on tree water use and for evaluating other methods of estimating water use.