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ARS Home » Pacific West Area » Davis, California » Crops Pathology and Genetics Research » Research » Research Project #436018

Research Project: Evaluating the Effectiveness of Surface Renewal and Other Technologies to Determine Almond Tree Water Use and Water Stress

Location: Crops Pathology and Genetics Research

Project Number: 2032-21220-008-015-T
Project Type: Trust Fund Cooperative Agreement

Start Date: Oct 1, 2018
End Date: Dec 31, 2020

1) Evaluate the effectiveness of the new stand-alone Surface Renewal (SR) method to accurately quantify almond orchard evapotranspiration (ET). 2) Compare stress indices from SR with several other methods to determine how effective they are for almonds. 3) Continue efforts to develop Infrared Radiometers (IRT) based measurements of ET using the surface renewal techniques.

1) A research grade surface renewal station along with an Eddy Covariance system was established in an almond orchard located at the Kearney Agricultural Center. The station will be equipped similarly to units those provided to growers by Tule Technologies. We will measure net radiation and ground heat flux directly, and also model net radiation and set daily G to zero to obtain ET estimates to assure commercial sensors perform equally well to research systems. ET estimates obtained from both types of surface renewal station will be compared to ET estimates recorded by the weighing lysimeter and eddy covariance located in the orchard. The weighing lysimeter will provide us with ET measurements that are considered to be the “gold standard” for accurately measuring crop ET. 2) We will measure ET with the surface renewal method for the 2017 growing season along with additional measurements to determine canopy water status. Midday values of leaf and stem water potential ('LEAF and 'STEM) and stomatal conductance (GS) will be measured with a pressure bomb and porometer, respectively, on weekly or biweekly basis using sun-exposed leaves from several locations in each block. Applied water quantity and irrigation frequency will be also be recorded. We will compare the ETC and stress indicators from SR with those obtained using IRT sensors (Crop Water Stress Index-CWSI and Stomatal Conductance Ratio-SCR) across the treatments, and determine why any differences are occurring (e.g. input data such as ET0 from closest CIMIS station). Canopy temperature measurements will be taken with IRTs on the canopy surrounding the area where the 'LEAF and stomatal conductance measurements are taken. This will be done using a research quality Apogee IRT connected to a datalogger. The McElrone lab has 20+ Apogee IRT sensors that can be used for continuous measurement throughout the two almond sites. The SCR and CWSI stress indices can provide valuable information to growers to help them plan their irrigation scheduling. These indices can be used to conserve water during growth stages where conserving water would have negligible impacts on yield. 3) Until now, SR has used air temperature measured by fine wire thermocouple temperature sensors. We are currently working with infrared temperature measurements SR mathematical methods to obtain ET estimates, and are finding promising results. We will implement this research over almond canopies in our study. If IRT can replace thermocouple sensors in the surface renewal method this would mean that the IRT can be used to obtain both water use (ET from SR) and water stress estimates (CWSI and SCR).