Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/15/2002
Publication Date: 6/1/2002
Citation: SADLER, E.J., CAMP JR, C.R., EVANS, D.E., MILLEN, J.A. CORN CANOPY TEMPERATURES MEASURED WITH A MOVING INFRARED THERMOMETER ARRAY. TRANSACTIONS OF THE AMERICAN SOCIETY OF AGRICULTURAL ENGINEERS. 2002. V. 45. P. 581-591. Interpretive Summary: Commercially available, inexpensive, non-contact infrared thermometers (IRT) can be used to measure crop temperature, but concerns about their accuracy have been raised. Despite these concerns, their low cost ($210 US in 1995 per IRT) and ease of use make them an attractive alternative to research-grade sensors costing several times more. The low cost enables an array of multiple sensors to be put in place. We used 26 IRTs spaced along a center pivot machine that had been modified to apply irrigation water on 396 plots, each about 10 m (30 ft) square. This site-specific center pivot was used to irrigate some plots and not others, and the IRTs were tested under these conditions. Since the IRT array was moved through the field on the slow-moving machine running dry, the rise in temperature, usually, during the 3.5-hour trip had to be accounted for. Simply subtracting air temperature at the time of each IRT measurement was sufficient to remove most of the time-dependent effect. After this adjustment, differences in temperature between unirrigated and well-watered plots were sometimes 8 deg C (14 deg F), easily detected with the IRT array. Temperatures for the same treatment on different plots of the same soil type were often 3.5 deg C (6 deg F) different, and averages for different soil types were often up to 2.5 deg C (4.5 deg F) different. These results, not previously documented, emphasize the importance of managing water-related soil properties if making recommendations for site-specific farming. Recommendations using these results, combined with innovations such as the site-specific center pivot, for instance, make possible a more effective stewardship of the nation's increasingly scarce water resources.
Technical Abstract: Measurement of water stress and scheduling of irrigation are both enabled by non-contact infrared thermometers (IRTs). Technological advances have miniaturized IRTs and reduced power requirements so that inexpensive self-powered units are now commercially available. The objective of this work was to test a linear array of IRT sensors mounted on a center pivot irrigation machine, and to use this IRT array to examine spatial variation in water stress of corn under four irrigation treatments imposed on a highly-variable field with a center pivot equipped for site-specific irrigation and agrochemical application. An array of 26 IRTs was mounted on the pivot, which was run dry for a full circle on seven days during the 1999 corn growing season. Procedures were developed to adjust for temporal slew during the 3.5-hr measurement period. Significant differences were obtained among the varying water treatments, as expected, but also among plots within the same soil map unit, and also among soil map unit means. Distinct spatial patterns, not necessarily related to the 1:1200-scale soil map, were observed. These results emphasize the necessity to consider soil water relations during the development of management recommendations for site-specific agriculture.