Water Stress Effects On Spatially Referenced Cotton Crop Canopy Properties.

Crop canopy temperature is known to be affected by water stress. Canopy reflectance can also be impacted as leaf orientation and color respond to the stress. As sensor systems are investigated for real-time management of irrigation and nitrogen, it is essential to understand how the data from the sensors respond to different irrigation management and soil variability. USDA-ARS and the University of Missouri are studying cotton irrigation effects at the University’s Fisher Delta Research Center near Portageville. Cotton is produced with different center pivot irrigation treatments in large plots on a field with highly variable soils. In 2011, two irrigation treatments were included. In 2012, a variable rate irrigation (VRI) system on the center pivot will allow additional irrigation treatments. Apparent electrical conductivity data were collected from the field to characterize the soil variability. A mobile sensor platform containing sensors for canopy reflectance, temperature, and height, along with temperature and relative humidity of the air above the canopy was driven through the field multiple times during the growing season. Estimates of soil water deficit and measurements of soil water content from various locations in the field were made on the days the sensor data are collected. The field was harvested with a cotton picker with individual yield monitoring for each row. The results indicate how the canopy measurements vary with soil water content, soil texture, and crop size, as well as which properties or combinations of properties relate best to yield and whether the relationships are consistent throughout the growing season. These findings will guide researchers in designing real-time monitoring and control systems for center pivot irrigation systems and optimal use of VRI technology.