Submitted to: ASAE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 7/19/1999
Publication Date: N/A
Interpretive Summary: Efficient use of water in irrigated crop production requires that the optimum amount of water be applied at the correct time. Techniques for rapidly measuring whole fields are needed to determine when crops begin to experience water stress. Remotely sensed canopy temperature and reflected radiation, that instantly measure whole fields, were compared with leaf water potential, which directly measures plant water status from leaf samples, to determine how quickly a change in plant water status can be detected. Water application to corn and cotton growing under different levels of irrigation was reversed and the three methods were used to monitor crop water status. Canopy detected the change in plant water status within one day of that recorded by direct measurement and reflected radiation did not sense a change until approximately one week later. Canopy temperature detected the change in water status almost as quickly as the direct measurement and has the capability to monitor whole fields simultaneously. This study demonstrates the suitability of temperature for monitoring crop water status where high levels of production management are used on whole fields or subunits to optimize yield.
Technical Abstract: Water supply is a primary limiting factor to crop production and crop water status is essential information for crop production management decisions. Corn and cotton were grown under two constant soil water levels, and then the water levels were reversed while the change in water status was monitored. The purpose of the experiment was to compare the sensitivity of leaf water potential, crop canopy temperature, and spectral reflectance to the change in crop water status. The low water level (WL) of corn was 0.66*PET and the high water level (WH) was 1.0*PET. The cotton WL was dryland, and the WH was 1.0*PET. The transient soil water treatments began on a day of scheduled irrigation which was 9 July (DOY 190) in corn and on 21 July (DOY 202) in cotton. A change in leaf water potential occurred five days after reversing water levels in corn and after three days in cotton. A change in canopy temperature level between the TLH and THL treatments, expressed as the amount of time that the temperature was >28 degrees C eac day (DST), was not detected after 25 d in corn, but a change in cotton was noted after 4 d. Spectral reflectance of the TLH and THL treatments was different prior to switching water application input. The normalized difference vegetative index (NDVI) of corn and cotton THL than the TLH treatments soil water levels were reversed. Separated from their initial water levels after 15 days and 8 days, respectively. Canopy temperature was sensitive to the change in crop water status and can rapidly determine conditions in an entire field.