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Title:   Author  item
                                            Wanjura, Donalditem
                                            Mahan, Jamesitem
                                            McMichael, Bobbieitem
                                            Gitz, Dennisitem
                                            Upchurch, Dan
  Submitted to: National Cotton Council Beltwide Cotton Conference
                                    Publication Type: Proceedings
                                    Publication Acceptance Date: 12/31/2005
                                    Publication  Date: 6/12/2006
                                    Citation: Wanjura, D.F., Mahan, J.R., McMichael, B.L., Gitz, D.C., Upchurch, D.R. 2006. Cotton response to multiple irrigation rates controlled by a constant time threshold [abstract]. In: Proceedings of the Beltwide Cotton Conferences, January 3-6, 2006, San Antonio, Texas. 2006 CDROM.Interpretive Summary: 
The Biologically Identified Optimal Thermal Interactive Console (BIOTIC) protocol for timing irrigation has the capability of automated 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 one-year study with cotton used subsurface drip irrigation and specific irrigation rates were applied in response to each irrigation signal. Irrigation rates from 0.08 to 0.32 inches per irrigation event were evaluated. Irrigation rates were highly correlated with cumulative irrigation and lint yield. An irrigation rate of 0.24 inches resulted in cumulative irrigation of 9.0 inches and produced the highest lint yield. Multiple irrigation rates in conjunction with a fixed time threshold produced a consistent response in the region of deficit irrigation.
                                Technical Abstract: 
A cotton irrigation study was managed using the BIOTIC protocol with a time threshold of 5.5 h and applying irrigation rates of 2, 4, 6, or 8 mm in response to an irrigation signal. The objective of the study was to measure the irrigation frequency and amount that results from using a fixed time-threshold to generate irrigation signals and applying variable quantities of water 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 was 1.4, 1.6, 2.2, and 2.2 d for irrigation rates of 2 mm, 4 mm, 6 mm, and 8 mm, respectively. Cumulative irrigation was positively related to irrigation rate. Daily stress time (DST) was calculated as the amount of time each day when the canopy temperature  > 28°C. Average DST declined linearly as irrigation rate increased. Leaf water potential was statistically different among all irrigation rate treatments with higher values occurring in the higher irrigation rate treatments. Leaf area index at first bloom was ~ 1.5 in the 2 mm treatment and 1.9, 2.0, and 2.2 in the 4 mm, 6 mm, and 8 mm treatments, respectively. Lint yield increased linearly up to a cumulative irrigation of 9.0 in, which was applied by the 6-mm irrigation rate, the highest rate that remained in the deficit irrigation region. Irrigation water use efficiency (IWUE) declined in a curvilinear manner with increasing irrigation amounts from 4.0 to 12.0 inches.


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