Submitted to: Irrigation Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/14/2000
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. Methods for rapidly measuring whole fields are needed to determine when crops begin to experience water stress. Remotely sensed canopy temperature was 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 two methods were used to monitor crop water status. Canopy temperature detected the change in plant water status of cotton within one day of that recorded by directly measuring leaf water potential, but was unable to sense the change in corn. 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 demonstrated the suitability of temperature fo monitoring cotton water status, but corn requires additional study where high levels of production management are used on whole fields or subunits to optimize yield.
Technical Abstract: Water application is a limiting factor to crop production and this crop water status is essential information for management decisions. Corn and cotton were grown in the field under two constant water application rates. The low water level (WL) of corn was 0.66*PET (potential evapotranspiration) and dryland for cotton. The high water level (WH) was 1.0*PET for both crops. Two transient treatments in each crop began as constant water levels and then the water inputs were reversed while the change in water status was monitored. The purpose of the experiment was to compare the sensitivity of leaf water potential (LWP) and crop canopy temperature to changes in irrigation rate. The LWP values of the transient water treatments reversed five and eight days after reversing water input rates to corn in 1998 and 1999, respectively, and after 3 days in both years for cotton. A reversal in canopy temperatures, expressed as the amount of daily time that the temperature was above 28 C (DST), was not detected between the TLH and THL treatments of corn after 25 days in 1998 or after 13 days in 1999. The DST values of the cotton transient treatments reversed after four days in 1998 and 5 days in 1999 when the values of THL became greater than for TLH. Corn tassels were forming at the beginning of the water reversal period and their presence in the view of the infrared thermometer may have reduced the apparent radiometric temperature difference between the transient treatments. Following the reversal of water application rate, LWP and DST were correlated in cotton in both years and only in 1998 in corn. Cotton canopy temperature was sensitive to change in LWP and could rapidly determine conditions in an entire field.