Submitted to: American Society of Agricultural Engineers Meetings Papers
Publication Type: Proceedings
Publication Acceptance Date: 7/23/2003
Publication Date: 7/23/2003
Citation: WANJURA, D.F., UPCHURCH, D.R., MAHAN, J.R. CROP WATER STATUS CONTROL WITH TEMPERATURE-TIME THRESHOLD IRRIGATION. AMERICAN SOCIETY OF AGRICULTURAL ENGINEERS MEETINGS PAPERS. 2003. Paper No. 032136. Interpretive Summary: Center pivot and subsurface drip irrigation systems have gained wide acceptance because of their capability to effectively control the frequency and amount of irrigation. A dependable and useable method of timing irrigation is needed. A common sympton of plants which are water stressed is high leaf temperature. Daily cumulative time that leaf temperature remains above specific temperature thresholds (stress time) can be used to indicate the need for irrigation. A method is described for selecting specific values of stress time (time thresholds) that produce different water input levels and cotton yield. A linear relationship was identified between stress time and lint yield. Linear relationships were also established between stress time and total water or irrigation input. Then one-hour differences in stress time were found to produce sufficiently large differences in total water and irrigation input that also produced different yields. For a semi-arid environment time thresholds of 330, 390, and 450 min/day above 28 C for cotton produced significant differences in irrigation and cotton yield. A test of this procedure in the 2002 growing season used time thresholds of 330 and 450 min/day, the lint yield produced was as predicted and 84 percent of predicted, respectively. The appropriate choice of a time threshold depends on the combination of available irrigation water and the targeted yield production level.
Technical Abstract: Center pivot and subsurface drip irrigation systems can accurately apply variable quantities of irrigation. A robust irrigation timing protocol that can function in variable environments is needed to maximize crop use of available water. Canopy temperature (TC) has been successfully used to time irrigation applications for well-watered crop growing conditions. The cumulative daily time that TC exceeds a crop specific temperature threshold, designated as stress time (ST), is used to indicate the need for irrigation. The ST value that generates the irrigation signal is the time threshold (TT). Manipulation of the TT value changes irrigation frequency and seasonal irrigation quantity. A procedure is described for estimating the relationship between TT for cotton and quantity of water input. Data were analyzed from multiple studies that included a common control TT of 330 min/day above a canopy temperature threshold of 28 C as the irrigation signal criteria for well-watered cotton. Daily ST averaged over the irrigation season was correlated with cotton yield and water input. A procedure for identifying control TT to establish different crop water status levels is described. Average TT values were 408, 468, and 528 min/day, which corresponded with control TT values of 330, 390, and 450 min/day. These control TT should result in different water application amounts during the growing season and produce different cotton yields.