Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/4/2005
Publication Date: 1/6/2005
Citation: Wanjura, D.F., Upchurch, D.R. 2005. Establishing different cotton water levels using multiple temperature-time thresholds. In: Proceedings of the Beltwide Cotton Conferences, January 4-7, 2005, New Orleans, Louisiana. 2005 CDROM. Interpretive Summary: The Biologically Identified Optimal Thermal Interactive Console (BIOTIC) method for timing irrigation has the capability of controlling different soil water regimes for cotton production using measured canopy temperature. An essential component in the method is a temperature-based index identified as stress time (ST) that monitors the water stress level of the crop and produces the signal to irrigate. Stress time is the daily accumulation of time while the crop's canopy temperature is warmer than the optimum temperature of the crop. A 2-year study with cotton used subsurface drip irrigation and specific ST levels to determine when irrigation was applied. Stress times between 5.5 and 8.5 hours/day were evaluated. The specific ST levels were highly correlated with amount of irrigation and yield in each year. In addition average ST during the irrigation period had a single common relationship for estimating cotton yield for the combined years. These results indicate the consistency of ST for controlling multiple irrigation regimes under the different growing environments present between years.
Technical Abstract: Subsurface drip irrigated cotton was controlled by the BIOTIC (Biologically Identified Optimal Thermal Interactive Console) irrigation timing protocol in 2003 and 2004. Specific amounts of daily stress time, referred to as time thresholds (TT) established different irrigation levels in cotton. Stress time (ST) occurred whenever canopy temperature was above 28°C. In the two-year study TT from 5.5 hr to 8.5 hr in 1-hr increments automatically controlled irrigation levels, which ranged from well-watered to significant deficit irrigation. Irrigation decisions were made daily and 5-mm irrigation was applied in response to irrigation signals in all time thresholds. The study's primary objective was to compare irrigation levels produced by the range of TT within years and the consistency of irrigation control of each TT between years. The year 2003 began with a dry soil profile and 2004 was wet. Rainfall during the irrigation period (DOY 187 to DOY 243) was 18 mm in 2003 and 95 mm in 2004. Heat units from May through October were 2512 in 2003 compared with 2250 DD60s in 2004. The relative amounts of irrigation applied by the different TT were consistent between years averaging 100%, 84%, 56%, and 23%, respectively for 5.5 hr TT, 6.5 hr TT, 7.5 hr TT, and 8.5 hr TT. In each year TT exhibited separate linear relationships with number of irrigation events, and lint yield. Slopes of the linear regressions between TT and number of irrigation events were '10.2 and '8.7 irrigations per 1 hr change in TT in 2003 and 2004, respectively. The slope coefficients in regression equations between TT and lint yield estimated that lint yield declined at the same rate of 202 kg lint ha-1 per 1-hr increase in TT value in each year. ST for each TT treatment were calculated for three groups of days during the irrigation period: (a) all days, (b) days when irrigation signals occurred, and (c) days without irrigation signals. Average daily ST for each group of days exhibited significant common linear relationships with lint yield for the combined years. Specific ST values provided daily control over different irrigation regimes and average ST during the entire irrigation period was correlated with lint yield. These applications of ST show this simple index to be a useful indicator of crop water status.