Irrigation scheduling based on crop canopy temperature for humid environments

Authors: BOCKHOLD, DANIEL - Natural Resources Conservation Service (NRCS, USDA); THOMPSON, ALLEN - University Of Missouri; Sudduth, Kenneth - Ken; HENGGELER, JOSEPH - University Of Missouri

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2011
Publication Date: 12/15/2011
Citation: Bockhold, D.L., Thompson, A.L., Sudduth, K.A., Henggeler, J.C. 2011. Irrigation scheduling based on crop canopy temperature for humid environments. Transactions of the ASABE. 54(6):2021-2028.

Interpretive Summary: The use of infrared thermometers (IR) to measure canopy temperatures for irrigation scheduling has been successfully applied in arid environments. Functionality of this technique in humid areas has been limited due to the presence of low vapor pressure deficits (VPD) and intermittent cloud cover. This study evaluated an alternate scheduling method for humid environments based on comparing canopy temperature with calculated canopy temperature of a well-watered crop. Irrigation was applied when the canopy temperature was greater than the predicted temperature for more than three consecutive hours for two consecutive days. This method was evaluated against well-watered, semi-stressed, and dryland treatments of corn, soybean, and cotton on the basis of grain yield and irrigation water use efficiency (IWUE). Canopy temperature was underpredicted when the vapor pressure deficit was greater than 2 kPa. Limiting data to conditions when the solar radiation was greater than 200 W m-2 and Richardson number was less than 0.2 resulted in excellent prediction of canopy temperatures for cotton but corn temperatures were still underpredicted. Although soybean and cotton yields were not significantly different across treatments, IWUE was improved for corn and cotton by use of this technique. Corn yield was greater for the well-watered crop but the IR method resulted in 85 percent of the maximum yield while requiring less than 50 percent of the irrigation water. This method shows promise as a tool for irrigation scheduling in humid environments. Further refinements are needed to incorporate periods of high VPD.

Technical Abstract: The use of infrared thermometers (IR) to measure canopy temperatures for irrigation scheduling has been successfully applied in arid environments. Functionality of this technique in humid areas has been limited due to the presence of low vapor pressure deficits (VPD) and intermittent cloud cover. This study evaluated an alternate scheduling method for humid environments based on comparing canopy temperature with calculated canopy temperature of a well-watered crop. Irrigation was applied when the canopy temperature was greater than the predicted temperature for more than three consecutive hours for two consecutive days. This method was evaluated against well-watered, semi-stressed, and dryland treatments of corn, soybean, and cotton on the basis of grain yield and irrigation water use efficiency (IWUE). Canopy temperature was underpredicted when the vapor pressure deficit was greater than 2 kPa. Limiting data to conditions when the solar radiation was greater than 200 W m -2 and Richardson number was less than 0.2 resulted in excellent prediction of canopy temperatures for cotton but corn temperatures were still underpredicted. Although soybean and cotton yields were not significantly different across treatments, IWUE was improved for corn and cotton by use of this technique. Corn yield was greater for the well-watered crop but the IR method resulted in 85 percent of the maximum yield while requiring less than 50 percent of the irrigation water. This method shows promise as a tool for irrigation scheduling in humid environments. Further refinements are needed to incorporate periods of high VPD.