Skip to main content
ARS Home » Midwest Area » Columbia, Missouri » Cropping Systems and Water Quality Research » Research » Publications at this Location » Publication #195937
Title: EFFECT OF ET CALCULATION METHOD ON IRRIGATION SCHEDULING IN MIDSOUTH

Author
item VORIES, EARL
item TACKER, P - UNIV OF AR COOP EXT SVC

Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 5/12/2006
Publication Date: 7/9/2006
Citation: Vories, E.D., Tacker, P. 2006. Effect of ET calculation method on irrigation scheduling in midsouth. ASABE Annual International Meeting, July 9-12, 2006 Portland OR. P.062205, unpaginated CDROM

Interpretive Summary: One of the computer programs used by farmers to help them know the appropriate times to irrigate their crops, the Arkansas Irrigation Scheduler, has been in use for over twenty years in Arkansas and surrounding states. The current version was released in 2000, and a new version is currently being developed. The new version will allow users to change the way the program estimates water use; however, care must be exercised because changing the method of estimating water use will impact irrigation recommendations. This work showed how the number of recommended irrigations differed when using two established methods for calculating water use. Properly scheduling irrigation can save farmers energy and therefore money by reducing unnecessary pumping, and help to alleviate water shortages being experienced in many agricultural areas.

Technical Abstract: Irrigation scheduling is more complicated in humid regions than arid, due to factors such as cloudy weather, rainfall, and temperature swings caused by the movement of weather fronts. The Arkansas Irrigation Scheduler (Scheduler) has been used for over twenty years in Arkansas and surrounding humid-region states. The current version was released in 2000 and is currently being updated. The new version will allow users the option to input reference evapotranspiration (ETo) directly, rather than allowing the program to estimate it. The objective of this report was to determine the difference between irrigation schedules developed using the Penman-Monteith estimate for ETo and the minimal-data method currently employed in the Scheduler. As shown in this report, changing the method of calculating ETo values can impact the recommendations. Values calculated using the equations in the Scheduler were consistently greater and less variable than values for the same days calculated with the standardized Penman-Monteith equation. Hypothetical cotton irrigation schedules generated using the Scheduler ETo values called for initial irrigation an average of six days earlier than with the Penman-Monteith values and called for an additional two irrigations each year. Careful attention will be required if a user changes to a different ETO estimation method when the program allows ETo to be input directly.