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United States Department of Agriculture

Agricultural Research Service

Title: Time Thresholds for Canopy Temperature Based Irrigation

Authors
item Wanjura, Donald
item UPCHURCH, DAN

Submitted to: International Evapotranspiration Irrigation Scheduling Conference
Publication Type: Proceedings
Publication Acceptance Date: June 5, 1996
Publication Date: N/A

Interpretive Summary: A new irrigation scheduling device named BIOTIC (Biologically Identified Optimal Temperature Interactive Console) has been developed and patented by the U.S. Patent Office. This device can automate water management on center pivot and drip irrigation systems. It is also sensitive to individual field conditions through the real time measurement of crop temperatures. An integral part of the device is methodology for calculatin a location specific time threshold which is part of the information that determines the need for irrigation. Time thresholds are computed by a model that is based on an energy balance description of a crop using local environmental data. Time thresholds are a one time calculation for a specific location and describe average conditions. The time threshold model calculated average seasonal time threshold values for well-water cotton to be 6.9 hours, 4.6 hours and 6.9 hours for humid, semi-arid, and arid environments, respectively. These time threshold values have controlled irrigation scheduling of cotton in field demonstrations in each environment. BIOTIC is labor saving technology, which uses automated measurement of only one to three environmental parameters, and this relative simplicity should make it attractive for irrigation scheduling.

Technical Abstract: Daily accumulation of time, above 28 degrees C, for continuously measured crop canopy temperature was compared with an environmentally dependent time threshold to schedule irrigation. An irrigation signal was indicated when the daily time accumulation exceeded the threshold value. A time threshold model, based on an energy balance description for the crop, calculated time ethreshold values. The limitation of atmospheric humidity to transpiration and its effect on accumulating time above the temperature thresholds determined by comparing measured humidity of the air with a limiting relative humidity (LRH) value. The LRH was calculated for a wet bulb temperature 2 degrees C below the temperature threshold. Calculated average seasonal time threshold values for well-water cotton were 4.6 hours for Lubbock, TX, 6.8 hours for Shafter, CA, and 6.9 hours at Mississippi State, MS. Total number of irrigations in field experiments at Lubbock, TX, during g1991 and 1992 was negatively related to the time threshold value. A linear equation described the relationship between time threshold and the relative number of irrigations. Relative number of irrigations for 4 hour, 6 hour, and 8 hour time thresholds was estimated to be 77%, 62%, and 47% of the value for a 2 hour time threshold. A time threshold of 5.0 hours was used to schedule irrigation at Lubbock and Shafter in 1994. In these studies there was a negative linear relationship between time threshold value and relative number of irrigations.

Last Modified: 9/10/2014