Submitted to: Irrigation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/23/2001
Publication Date: N/A
Interpretive Summary: Demand is increasing for the nation's water supply. Agriculture, as the major water user in the west, must use irrigation water efficiently. Peaches, because they are green and growing from early spring until late fall, use a lot of water. We can predict the amount of water a crop needs from weather information. Crop coefficients convert this weather information to predicted water needs of the crop. In this study, we measured actual peach water use over several seasons in large (2 m x 4 m x 2 m deep)) weighing lysimeters (like large flower pots on scales) and compared this with the weather data, to determine the crop coefficient for peaches. By using these peach crop coefficients and weather information, farmers can precisely apply water to meet the tree's needs, and thus avoid over-irrigation.
Technical Abstract: A four year experiment was conducted using a large weighing lysimeter to determine the crop coefficient and crop water use of a late season peach cultivar irrigated with a surface drip system. Two trees were planted in a 2m by 4m by 2m deep weighing lysimeter that was surface irrigated with 2 L/hr in-line drip emitters. Irrigation was applied in 12 mm applications after a 12 mm water loss threshold was exceeded as measured by the lysimeter. The crop coefficient (Kc) was calculated using the measured water losses and grass reference evapotranspiration calculated using the CIMIS Penman equation. The Kc was plotted against the day of the year and linear, quadratic, and cubic regressions were fit to the data. A three segment linear and the cubic equation had the best fit to the data. The maximum Kc determined for the linear fit in this experiment was 1.06 compared to a maximum of 0.92 recommended for use in California and 0.98 calculated using the FAO method. Average water use for the 4 years of the experiment was 1034 mm. Midday canopy light interception was well correlated to the crop coefficient.