Automated irrigation based on threshold canopy temperature
1992
Wanjura, D.F. | Upchurch, D.R. | Mahan, J.R.
An automated drip irrigation system was controlled by continuously measuring cotton canopy temperature and computing 15-minute averages in a three-year field study between 1988-1990. Irrigation was applied only when average canopy temperature exceeded predetermined threshold values. Threshold temperatures were tested in 2 degrees C increments between 26 degrees C and 32 degrees C. The length of irrigation cycles was shortest and amount per irrigation event was highest for all threshold temperatures during the early growth stage because canopies were small and warm bare soil contributed to measured canopy temperature. The ratio of water use to reference evapotranspiration decreased as threshold canopy temperature increased from 26 degrees C to 32 degrees C, but water use efficiency increased. Average canopy temperature during the period DOY 198 to 273, while net radiation exceeded 300 W m-2 and air temperature at 2 m exceeded 28 degrees C, increased as threshold canopy temperature increased. Lint yield was highest for the 28 degrees C threshold temperature and decreased for higher or lower threshold temperatures. Threshold temperatures the 28 degrees C restricted water application and created increasing levels of water stress. The 28 degrees C threshold should provide maximum lint yield where water supply and season length do not limit production. Under limited production conditions a 30 degrees C threshold may be preferable to a 28 degrees C threshold because lint yield is only slightly reduced but water use efficiency is higher and cotton matures more rapidly. Maximum yields were produced by 28 degrees C and 30 degrees C threshold canopy temperatures in which total seasonal water use ranged between 64 and 84 cm.
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