|Fisher, Daniel - Ken|
Submitted to: Journal of Agricultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/23/2011
Publication Date: 4/4/2012
Citation: Thomson, S.J., Plamondon-Ouellet, C.M., Defauw, S.L., Huang, Y., Fisher, D.K., English, P.J. 2012. Potential and challenges in use of thermal imaging for humid region irrigation system management. Journal of Agricultural Science. 4(4):103-116. Interpretive Summary: Irrigation of crops depends on providing water at the right time and in the right amounts. Irrigation timing is a challenge because it is not always obvious when the crop is stressed enough to require water. Water applied too early can be wasteful, but water applied too late may have detrimental effects on crop yield and quality, thereby decreasing its value. In theory, an imaging system flown in aircraft that “takes the temperature” of the crop canopy can be used to determine areas of a field that require water. Warmer canopies signify higher crop water stress, and thermal information could be used to signal when irrigation is required. Spatial statistics shows relationships between many variables in space and, in this case, can be used to identify areas in a field where crop waterstress is more prevalent. Challenges in the use of thermal imagery to assist in scheduling irrigation are presented from our research. An example application using spatial statistics to analyze thermal imagery, crop cover changes, and crop yield is presented to identify problem field areas that may require different management. Irrigation scheduling is one aspect of irrigation system management; system diagnostics is another aspect. Two examples that use thermal imagery to diagnose leaking irrigation systems are described.
Technical Abstract: Thermal imaging has shown potential to assist with many aspects of irrigation management including scheduling water application, detecting leaky irrigation canals, and gauging the overall effectiveness of water distribution networks used in furrow irrigation. Many challenges exist for the use of thermal imagery to accurately determine temporal crop water stress to assist in timing irrigation based on crop water status. There are particular challenges for use of these technologies in humid subtropical climates, which include proper accounting for variations in solar radiation and wind on a spatiotemporal basis, delineating canopy-air temperature difference (CATD) under periods of low vapor-pressure deficit, taking care to account for sun angle, and accounting for altitude effects on canopy temperature represented at the camera. At the Crop Production Systems Research Unit (CPSRU) of the USDA, ARS in Stoneville, MS (USA), information from thermal imagery obtained with agricultural aircraft are being used along with ground-based readings of soil moisture status and canopy temperature to develop consistent criteria for scheduling irrigation. A review of pertinent issues involved in using thermal methods for sensing canopy temperature is presented that can be applied to the imaging problem, along with a proposed approach using spatial statistics that can enhance the value of thermal imagery for detecting water-stressed cropped areas. Thermal imagery has been used to identify plant canopy temperature differences related to crop water/heat stress, and we have applied spatial statistics to help to delineate areas of the field with high potential for crop water stress. Lastly, we illustrate the utility of thermal imagery for detecting leakage from irrigation canals and poly-pipe furrow irrigation systems.