Scanned and spot measured canopy temperatures of cotton and corn

Abstract

Canopy temperature is a useful indicator of crop water stress and can also be used for making timely irrigation scheduling decisions for center pivot and subsurface drip irrigation systems. However, it is not known how closely the measured canopy temperature from a circular area of the canopy surface compares with a larger continuous area that includes the full canopy width. A study was conducted in 2001 where canopy temperatures were measured with infrared thermocouples (IT) and a thermal scanner (TS) in field plots irrigated by surface drip irrigation using cotton ( Gossypium hirsutum L.) and corn ( Zea maize L.). Two water levels included full evapotranspiration replacement (high water, HW) in cotton and corn and a second water level in cotton (low water, LW), which received 50% of the HW cotton amount. The purpose of the study was to compare canopy temperature measured from a small canopy area using IT with that obtained from a larger area with a TS. Canopy temperatures in the HW cotton, and HW corn were measured on 8 days during a 20-day period that started at first bloom in cotton and the V14 growth stage of corn, including four successive days during one irrigation cycle. Differences in canopy temperature measured by the two sensors averaged 0.2 °C in HW cotton, 3.2 °C in LW cotton, and 0.6 °C in HW corn. When leaf cover within the canopy was sufficient to mask the soil background, canopy temperatures measured from a small area by IT were comparable to those from a larger area sensed by a TS.