Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: February 15, 1997
Publication Date: N/A
Interpretive Summary: Center pivot irrigation systems using low pressure discharge of water at the soil surface are gaining wide acceptance because of their capability to achieve improved control of frequency and amount of irrigation. A common symptom of plants which need water is high leaf temperature. An irrigation scheduling method based on continuously monitoring plant canopy temperature was used to control irrigation scheduling of cotton. Infrared thermometers were used to continuously measure the canopy temperature of cotton plants. Irrigation signals were tested which were based on the amount of time that plant temperature exceeded 28 degrees C during one day (time thresholds). Number of irrigation signals decreased linearly as the size of the time threshold increased between 4 and 8 hours. A time threshold of 6 hours provided sufficient irrigation to maximize lint yield and efficient use of water.
Technical Abstract: A cotton irrigation study was conducted at Lubbock, TX in 1995 using continuously measured canopy temperature to automatically apply water. The objective of the experiment was to determine the number of irrigations applied by different time thresholds and measure the response of cotton to periods of either water deficit or excess applied at different times during the season. Three irrigation levels were created by using stress times, accumulations of 4, 6, or 8 hrs above a canopy temperature threshold of 28 deg C, to produce irrigation signals. In addition to 3 normal water levels established by time thresholds of 4 h, 6 h, and 8 h, periods of water deficit and water excess were superimposed on each water level. Total irrigations of 39, 35, and 33 cm were applied by the 4 h, 6 h, and 8 h time thresholds, respectively. The number of irrigations applied in 1995 varied from 18 to 15 with no radiation level limitations on the accumulation of stress time. Restricting stress time accumulation to the daylight period when radiation was above 200 wm-2 improved the uniformity of irrigation control between 1995 and previous tests conducted in 1991 and 1992. Daily stress time and leaf water potential were linearly related among time threshold irrigation treatments. Daily stress time values were correlated with single, daytime leaf water potential measurements taken when the canopy was under maximum daily heat stress. There was no difference between the lint yields of 1404 and 1435 lbs/acre for the 4 h and 6 h time threshold treatments which were greater than the 1271 lbs/acre yield of the 8 h time threshold treatment.