Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/6/1999
Publication Date: N/A
Interpretive Summary: Water is the primary limitation to crop production in semi-arid environments. Under irrigation the optimum amount of water applied at the correct time are crucial factors for using water efficiently. Methods are needed that can rapidly measure whole fields to determine when crops require irrigation. Remotely sensed canopy temperature and reflected radiation, that instantly measure whole fields, were compared with the direct measurement of the water status of crop plants, that measures individual plants, to determine how quickly a change in plant water status can be detected. Water application to cotton growing under either dryland or full irrigation was reversed and the three methods were used to monitor water status. The direct measurement of plant water status detected the change after three days, canopy detected the change in four days, but reflected radiation did not detect any change after eight days. Canopy temperature detected the change in water status almost as quickly as the direct measurement and has capability of monitoring whole fields simultaneously. This study demonstrates the suitability of temperature for monitoring crop water status where high levels of production management are used on small land units to optimize whole field yield.
Technical Abstract: Water application is a primary limiting factor to crop production and thus water status of the crop is essential information for production management decisions. Cotton was grown under two constant levels of soil moisture and then the water levels were reversed while the change in water status was monitored at Lubbock, TX in 1998. The purpose of the experiment was to compare the sensitivity of leaf water potential, temperature of the crop canopy, and spectral reflectance to the change in water status of cotton. The low water level (WL) was dryland and the high water level (WH) was 1.0 *PET. The transient water treatment that relieved water stress was TLH which changed from WL to WH and the treatment which induced water stress was THL which changed from WH to WL. When the transient water treatments were initiated in the WL and WH treatments the growth stage was first bloom plus two weeks. A change in leaf water potential occurred after three days. .A change in canopy temperature between the TLH and THL treatments, expressed as the amount of daily time that the temperature was above 28 deg C (DST), was detected after four days. Spectral reflectance of the TLH and THL treatments was different between these treatments prior to switching water application input. The spectral reflectance in the near infrared (NIR) band and the normalized difference vegetative index (NDVI) remained consistently higher in the THL than the TLH treatment for 8 days after water application rates were reversed. Canopy temperature was sensitive to change in crop water status and can rapidly determine conditions in an entire field compared to leaf water potential which accurately measures water status but can not provide automated spatial measurements with current technology.