CROP WATER USE ( HARGREAVES ET EQUATION) NEW WOLFRAM ALPHA WIDGET. Reference: Hargreaves, G. H. and Z. A. Samani, Reference Crop Evapotranspiration from Temperature. Appl. Eng. Agric., ASAE. 1(2). 1985,. pp.96-99.
Widget Application: Suppose you want to schedule irrigation by replacing the water evapotranspired by your crop each day. 1. Click on the appropriate link to get yesterdays solar radiation for your location: Puerto Rico or Northern Caribbean, 2. Check the internet for the average daily air temperature at your location (average = (minimum + maximum)/2), 3. Get the appropriate crop coefficient for your crop from this link, and 4. Finally, enter solar radiation, air temperature and crop coefficient into the widget to estimate ET. Multiply ET x acres x 1069.0663 to get the number of gallons of water you need to apply to your field.