Choice of Irrigation Timing Indicator for Narrow Row Cotton1

Abstract

AbstractThis irrigation study was undertaken to compare water use efficiencies (WUE) resulting from three methods of timing water applications on narrow‐row cotton (Gossy‐pium hirsutum L.). Irrigation timing during the 1971 and 1972 growing seasons was accomplished using the soil water potential (SWP)‐fixed level, leaf water potential (LWP)‐fixed level, and stress day index (SDI)‐vari‐able level of LWP, based on crop sensitivities, as indicators. Specific levels of each indicator were selected so that nearly identical yields would result for all three timing indicators, thus making possible the valid comparison of WUE. With the SWP indicator as a basis for comparison, higher WUE were obtained with the LWP and SDI indicators in both years. At a plant population of 150,000 plants/ha, average increases in WUE (seed cotton yield divided by irrigation plus rainfall amounts) were 17 and 38% for the LWP and SDI indicators, respectively. Average increases when WUE was calculated as yield divided by irrigation amount only were 30 and 82%, respectively. The increases in WUE were due to reductions in irrigation amounts rather than increases in yield. These results demonstrate that significant benefits in stretching irrigation water supplies are possible when using plant‐based measurements and when plant sensitivities at different growth stages are quantitatively considered in timing irrigations.