Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 11/6/2006
Publication Date: 11/8/2006
Citation: Van Pelt, R.S., Gitz, D.C. 2006. Radiation and energy balance of a kaolin particle coated cotton crop[abstract]. ASA-CSSA-SSSA. 135. Interpretive Summary: In semi-arid agricultural regions, there is often more sunlight available than necessary to provide for maximum photosynthesis. The excess sunlight that is not reflected back to space is converted to heat and this heat, along with dry air masses, results in excessive water use and reduced crop water use efficiency. Kaolin particle coatings have been credited with crop yield increases. We instrumented a field with radiation and energy balance sensors to determine if the particle coatings reflected more incoming solar radiation back to space and if the lower net radiation resulted in cooler soil and canopy temperatures. We found that the kaolin particle coatings decreased net radiation by 2 – 4 %, decreased soil surface temperatures by up to 5 degrees C, and resulted in lower values of soil heat flux. The effects of the kaolin particle coatings on canopy temperatures was not as we expected and the temperatures were often the same or higher than uncopated canopies.
Technical Abstract: In semi-arid environments, clear skies and intense solar radiation may create stressful growing conditions for crops. In such environments, the radiation levels are often greater than the photosynthetically active radiation compensation point for a given crop and the excess radiation is converted to sensible heat. The increased sensible heat results in increased vapor pressure deficits, higher tissue temperatures, and reduced water use efficiency. Kaolin clay particle coatings applied to crop canopies have been shown to increase growth, yield, and quality of crops grown in several environments. We hypothesized that the coatings increase the albedo of the canopy and over-spray areas of the soil surface, thus reducing the net radiation, and resulting in cooler canopy and soil temperatures. In an experiment comparing the effects of kaolin coatings on the growth and yield of two varieties of cotton, we instrumented plots with split-band net radiometers to measure the effects of the kaolin coatings on albedo and with infrared thermocouples focused on the canopy and soil to measure the effects on canopy and soil surface temperatures. We found that the kaolin particle coatings increased the albedo between 2 and 4 % depending on the time after application and that the soil surface temperatures of the treated plots were cooler than the untreated controls. However, canopy temperatures measured remotely with infrared thermocouples were up to 5oC warmer for the treated plants than for the untreated. These results indicate that remote measurement of particle coated canopy temperatures may not be possible.