Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/9/2007
Publication Date: 1/12/2007
Citation: Wanjura, D.F., Gitz, D.C., Mahan, J.R., Mcmichael, B.L., Upchurch, D.R. 2007. Cotton Response to Multiple Irrigation Rates Controlled by a Common Time Threshold. Proc. Beltwide Cotton Conference. New Orleans, Lousiana. January 9-12, 2007. Natl Cotton Counc. Am., Memphis, TN. Interpretive Summary: The Biologically Identified Optimal Thermal Interactive Console (BIOTIC) protocol for timing irrigation automates control of soil water regimes for crop production. One of the factors that control soil water level is the amount of water applied (irrigation rate) when an irrigation signal occurs. The maximum irrigation rate is also directly related to the output capacity of irrigation wells. A two-year study with cotton used subsurface drip irrigation and multiple irrigation rates were applied in response to a common irrigation signal. Four irrigation rates between 0.08 to 0.32 inches per irrigation event were evaluated. Within years irrigation rates were highly correlated with cumulative irrigation and lint yield. Irrigation rates of 0.24 and 0.32 inches in 2005 and 2006 applied total irrigations of 9.0 and 12.0 inches, respectively, and produced the highest lint yield. The consistency between years was not in total irrigation that produced maximum yield, but these irrigation amounts represented 80% of full crop evapotranspiration in both years.
Technical Abstract: A 2-year cotton study was irrigated using the BIOTIC protocol with a time threshold of 5.5 h > 28°C and applied irrigation rates of 2, 4, 6, or 8 mm in response to an irrigation signal. The objective was to measure the irrigation frequency and amount that results from using a fixed time-threshold to generate irrigation signals with variable quantities of water applied in response to irrigation signals. Irrigation was initiated during the squaring-growth stage and was terminated in each treatment when boll maturity reached 40%. The average time between irrigations for the two years was 1.6, 1.8, 2.2, and 2.4 d for irrigation rates of 2, 4, 6, and 8 mm, respectively. Cumulative irrigation was positively related to irrigation rate. Daily stress time (DST), calculated as the amount of time each day when the canopy temperature > 28°C, declined linearly as irrigation rate increased. Leaf water potential was statistically different among all irrigation rate treatments with smaller negative values occurring in the higher irrigation rate treatments. Lint yield increased linearly up to irrigation amounts of 9.0 and 12.0 inches, respectively, in 2005 and 2006. These irrigation quantities represented 80% of full crop evapotranspiration (ET) in both years. The differences in irrigation and rain during the boll setting and boll maturation growth stages could have produced the curvilinear and linear responses of burcotton yield to amount of irrigation in 2005 and 2006, respectively.