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Title: Evapotranspiration Adjustments for Deficit Irrigated Corn Using Canopy Temperature: A Concept

item Bausch, Walter
item Trout, Thomas
item Buchleiter, Gerald

Submitted to: Journal of Irrigation and Drainage
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2010
Publication Date: 12/17/2010
Citation: Bausch, W.C., Trout, T.J., Buchleiter, G.W. 2010. Evapotranspiration Adjustments for Deficit Irrigated Corn Using Canopy Temperature: A Concept. Journal of Irrigation and Drainage. Irrigation and Drainage ( DOI:10.1002/ird.601.

Interpretive Summary: Water deficits must be imposed on crops during noncritical growth periods to maximize use of limited water supplies for agricultural crop production. Irrigation timing and irrigation amount determinations under such a scenario are not the same as for fully irrigated crop production. Water stress encountered by the crop must be assessed and quantified by measurement of some plant stress indicator to determine the reduction in crop evapotranspiration (ET). Temperature of the crop is an easy to measure stress indicator using thermal infrared sensors. The objective of this study was to investigate use of canopy temperature measured with infrared thermometers to determine if a ratio of canopy temperature of fully-irrigated corn divided by the canopy temperature of water-stressed corn could be used as a stress coefficient to adjust crop ET. Preliminary results indicated that this ratio may be a useful quantitative water stress coefficient for incorporating plant stress effects into crop ET estimates.

Technical Abstract: Sustainability of irrigated agriculture with declining water supplies is a critical agricultural issue in the US Great Plains. Consequently, the paradigm of maximizing production through full irrigation must be abandoned. Imposing water deficits on crops during non-critical growth periods must be implemented to maximize net economic output per unit of water consumed by the plant. An irrigation timing and amount determination for such a scenario is not a simple, straight-forward procedure. Methods that monitor plant stress indicators would appear to be most promising. Several canopy temperature based irrigation timing techniques exist that determine when to irrigate but do not indicate how much to irrigate. The reference ET-crop coefficient procedure for determining crop ET which is used in fully irrigated crop conditions would be easiest to implement; however, the water stress coefficient used in that procedure may not be applicable for prolonged periods of water stress. The objective of this study was to investigate use of a ratio of canopy temperature (Tc) measured over fully irrigated and water stressed corn (Zea mays L.) as a substitute for the water stress coefficient presently used in the reference ET-crop coefficient concept. Preliminary results indicated that the Tc ratio is a reasonable quantitative water stress coefficient for calculating crop ET under water stress conditions. This ratio allows application of the crop coefficient method for scheduling deficit irrigation. Furthermore, the Tc ratio lends itself to hourly incorporation of plant stress effects on crop ET since canopy temperature can be measured continuously throughout the day.