Submitted to: Irrigation Association Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 11/15/2008
Publication Date: 11/30/2008
Citation: OShaughnessy, S.A., Evett, S.R., Colaizzi, P.D., Howell, T.A. 2008. Soil water measurement and thermal indices for center pivot irrigation scheduling. International Irrigation Association Conference, November 2-4, 2008, Anaheim, California. 2008 CDROM Interpretive Summary: Well-timed and adequate irrigation is necessary for successful crop production. However, scheduling irrigations at the proper time is not easy. Many farmers manage large fields or a number of different fields. In the Texas High Plains, the majority of irrigated crops are watered with center pivot systems. If a farmer can rely on a method to schedule irrigations only when the crop needs the water, it may help them to produce a good crop with less water or decide what crops to plant with the amount of water they have available. Two methods of triggering an irrigation were inspected, one using canopy temperature read from infrared thermometers and the other using canopy temperature and data from a weather station. Neither of these methods is without problems, but studying different methods of using information from the plants and the weather will help to improve the efficiency of water applied to a crop and may save a farmer valuable time.
Technical Abstract: In this two-year study, the relationship between irrigation scheduling using soil water measurements, and two thermal indices was investigated. One-half of a three-span center pivot irrigated field was planted to cotton in circular rows and irrigated with LEPA (low energy, precision application) drag socks in furrow dikes. Infrared thermometers (IRTs), used to measure crop canopy temperature, were mounted on the center pivot spans. Replicated treatments established radially from the pivot point, received four amounts of water, 100%, 67%, 33% and 0%, where 0% was dryland (Dry) and the 100% amount was based on either soil water replenishment to field capacity (manually initiated) or on the automatic irrigation protocol called the Time Temperature Threshold (TTT) method. Three sectors (blocks) of radial plots were irrigated on odd-numbered days of year (DOY) based on neutron moisture meter (NMM) soil water measurements in a 1.5-m profile, while three sectors were irrigated automatically on even-numbered days based on the TTT method. Average cotton lint-yields, dryland, and water use efficiencies for 2007 were not significantly different between the automatic and manual blocks. Averaged paired yields for each irrigation level were only significantly different between manual and automatic blocks in the 67% treatment. A post analysis of the daily theoretical CWSI was performed and compared to a predetermined TTT index for each day during the period of automatic irrigation scheduling, showing that 92% of the automatic irrigation triggers occurred when the TTT index > 450 minutes and the theoretical CWSI was > = 0.5 for the two growing seasons. Combining the theoretical CWSI with a TTT index may improve automatic irrigation scheduling. Yield data for 2008 were not yet available.