Submitted to: 2003 Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/6/2003
Publication Date: 1/10/2003
Citation: WANJURA, D.F., UPCHURCH, D.R., LASCANO, R.J. SUBSURFACE DRIP IRRIGATION OF COTTON USING TIME THRESHOLDS. PROCEEDINGS OF 2003 BELTWIDE COTTON CONFERENCE. 2003. P. 554-562. Interpretive Summary: The BIOTIC method for timing irrigation applications has been demonstrated to be useful in managing surface applied irrigation with the capability of producing different soil water regimes for crop production. A critical component in the method is the time threshold which determines the level of crop water stress and issues the irrigation signal. The increasing use of subsurface drip irrigation (SDI) creates the potential for higher crop yields and greater efficiency of water use. A study was conducted using SDI and a range of time thresholds with cotton for the purpose of estimating the time threshold values that best match the range of available water supplies produced from irrigation wells. A long term objective is to conduct multi-year studies to determine the stability of soil water levels established by different time thresholds. Time thresholds of 2.5 and 5.5 hours produced cotton yields of 1420 and 1390 lbs. lint per acre compared to 910 for at time threshold of 7.5 hours. Irrigation applied was 15.7, 12.3, and 7.9 inches; respectively, for 2.5 hr, 5.5 hr, and 7.5 hr time thresholds. The 5.5 hr time threshold produced the most optimum water level of the three time thresholds by producing 98 % of maximum yield with 21 % less irrigation.
Technical Abstract: Technical Abstract Subsurface drip irrigation systems have high initial cost, which must be recovered through some combination of higher water use efficiency and yield to increase net return. Canopy temperature (TC) was used in a field study to measure stress time (ST) in cotton, which is the daily accumulation of time when TC > 28 °C. Three levels of ST, 2.5 hr, 5.5 hr, and 7.5 hr, were used as irrigation signal criteria and referred to as time thresholds (TT). The purpose of the study was to measure the effect of different time thresholds values on the quantity of irrigation applied and their effect on lint yield and efficiency of water use. Daily irrigation decisions were made and 5 mm quantities were applied in response to each irrigation signal. During the entire irrigation period, the 2.5 hr TT treatment received 78 (82% of days) irrigation signals, the 5.5 hr TT generated 60 (63%) irrigation signals, and the 7.5 hr TT had 35 (37%) irrigation signals. For days when an irrigation signal occurred, average daily ST was 353 (5.9 hr), 418 (7.0 hr), and 485 (8.1 hr) min. for 2.5 hr, 5.5 hr, and 7.5 hr TT, respectively. Total irrigation applied during the growing season was 398, 313, and 201 mm, respectively to 2.5, 5.5, and 7.5 hr TT treatments. Total water applied to the treatments was 577, 492, and 380 mm through the completion of crop maturity. Highest lint yields of 1588 kg ha-1 and 1555 kg ha-1 produced by the 2.5 hr and 5.5 hr treatments, were not statistically different, and both were higher than the 1018 kg ha-1 yield from the 7.5 hr TT. Dryland yield was 307 kg lint ha-1. Irrigation water use efficiency was 50 and 51 kg lint ha-1 cm-1, respectively, for 5.5 hr TT and 7.5 hr TT, and both were higher than the 40 kg lint ha-1 cm-1 measured from 2.5 hr TT. Total water use efficiency was highest for the 5.5 hr TT (32 kg lint ha-1 cm-1) and slightly less for the 2.5 hr TT (28 kg lint ha-1 cm-1) and 7.5 hr TT (27 kg lint ha-1 cm-1). The 5.5 hr TT produced the most favorable results when measured by the combined standards of yield and efficient use of water.