Dr. Florence Cassel Sharma, Fresno State - Lysimetric Determination of Evapotranspiration Coefficients for Drip-irrigated Vegetables

Co-investigators: Dr. Dave Goorahoo (Fresno State), Mr. Shawn Ashkan (Fresno State), Mr. Forrest Melton (CSU, Monterey Bay), Mr. Lee Johnson (CSU, Monterey Bay).

ARI funding commitment: $449,870; Matching Funds: $464,775.

In response to prolonged drought and environmental concerns, crop production in California is migrating from flood irrigation to low-pressure drip irrigation systems. While drip irrigation has increased water use efficiency, adopting management practices that schedule irrigation based on crop water requirements by estimating crop evapotranspiration (ET) based on crop coefficients (Kc) can drive optimization further.

Determining daily ET values for site-specific climatic conditions and cultural practices is difficult, so few growers manage their crops with this method. The project being led by Dr. Sharma, will develop crop coefficients for drip irrigated fresh-market onions by implementing lysimetric and surface renewal studies.

As the crop grows, the ratio of crop cover to bare ground changes, and the crop water requirements become greater. The accuracy of crop coefficients can be improved by including estimates of crop cover, which can be estimated by remote sensing of the crop by satellites. CSU Monterey Bay/ NASA Ames Research Center scientists Melton and Johnson will provide that expertise to the project.

Once completed, the data will be integrated into irrigation programs (WATERIGHT and CropManage) that can be used by growers to schedule irrigation. While not site-specific, the Kc curves they are developing will be based on growing degree days. This should increase the accuracy in crop water requirements across different locations and climates and lead to greater use by growers.