An Integrated Lysimeter and Satellite Imagery Approach for Estimating Crop Evapotranspiration

Thursday, 18 December 2014
Dave Goorahoo, California State University Fresno, Fresno, CA, United States, Florence Cassel-Sharma, CSU Fresno, Fresno, CA, United States, Lee Johnson, Univ. Corp. Monterey Bay, Moffett Field, CA, United States and Forrest S Melton, California State University Monterey Bay, Seaside, CA, United States
Accurate estimation of crop water requirement (CWR) is essential for the implementation efficient irrigation schedules in an effort to optimize water use efficiency. This is particularly important in the central San Joaquin Valley (SJV), California, USA, where severe droughts have accentuated the need to conserve water and improve on-farm water management. In the current study, we adopt an integrated approach for estimation of crop evapotranspiration (ETc) involving the use of weighing lysimeters and satellite imagery. In the first phase of the study with the crop lysimeter, conducted on a clay loam soil with processing tomatoes grown under sub-surface drip irrigation, observations of crop ground cover were conducted weekly and evapotranspiration (ET) data were collected daily to derive relationships between crop coefficients and fractional cover. Data collected during the first year of the study, indicted that the crop coefficients (Kc) obtained at peak season were relatively higher than those generally reported for tomatoes commonly grown in the central SJV. Overall, there was a good correlation between fractional cover and crop coefficients (r2 = 0.91), with the average peak ET and Kc values ranging from 6 to 7 mm per day and from 0.8 to 0.9, respectively. Data obtained from satellite imagery, representing relatively larger spatial measurements than the lysimeters, are being compared with the surface observations from the lysimeters and will also be discussed in our presentation.