Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/15/2012
Publication Date: 5/15/2012
Citation: O'Shaughnessy, S.A., Evett, S.R., Colaizzi, P.D., Howell, T.A. 2012. Grain sorghum response to irrigation scheduling with the time-temperature threshold method and deficit irrigation levels. Transactions of the ASABE. 55(2):451-461. Interpretive Summary: Site-specific irrigation management can possibly increase crop water productivity by providing only the necessary amount of water that a crop needs during critical growth stages. In the Texas Panhandle region, grain sorghum is an important crop. Typically, both late and early maturing varieties are cultivated and irrigated at a deficit level. Plant-feedback or canopy temperature can be used to help schedule irrigations with reduced management time. In this two-year study, the Time Temperature Threshold (TTT) method was used to automate irrigation control of grain sorghum. Yields from the automatic treatment plots were compared to those that were irrigated based on crop water use, measured weekly with the neutron probe. Four deficit levels of irrigation were applied (80, 55, 30, and 0 percent of soil water depletion to field capacity) to evaluate the maximum crop water use efficiency. Sorghum canopy temperatures were remotely monitored by wireless infrared thermometers located on a pivot lateral. As the pivot moved, canopy temperatures and the geo-spatial location of the pivot lateral were recorded. If the average canopy temperature of sorghum plants located in the well-irrigated automatic plots was greater than an established set point for more than 315 minutes during a 24 hour period of time, an irrigation signal was generated. Irrigation amounts in the Manual plots were based on weekly neutron probe readings. The amount was divided into three irrigations and delivered on odd days of the year during the week. Grain yields from the automatic controlled irrigation plots were similar to those produced in the manual plots for three of the four irrigation treatment levels (80, 55, and 0) during 2009. Yields were similar or better than those in for all four treatment levels in 2010. This indicates that sorghum is responsive to the TTT method of irrigation scheduling. The greatest water use efficiency was realized in the 55% treatment for both years for both the automatic and manual methods of irrigation control.
Technical Abstract: Studies using the Time Temperature Threshold (TTT) method for irrigation scheduling have been documented for cotton, corn, and soybean. However, there are limited studies of the irrigation management of grain sorghum (Sorghum bicolor, L.) with this plant-feedback system. In this two-year study, the TTT method was investigated as an automatic irrigation control algorithm for a late maturing grain sorghum hybrid (Pioneer 84G62) grown in 2009, and an early maturing hybrid (Moench, NC+ 5C35) grown in 2010. The method was evaluated by comparing crop evapotranspiration (ETc), yield response, water use efficiency (WUE), and irrigation water use efficiency (IWUE) between automatic and manual control methods of irrigation scheduling at different deficit irrigation treatments (i.e., 80%, 55%, 30% and 0% of full replenishment of soil water depletion to 1.5 m depth). In 2009, the two irrigation control methods produced similar average dry grain yields in the 80%, 55%, and 0% treatment plots. Mean crop WUE was not significantly different between irrigation methods at any treatment level. In 2010, mean values of biomass and dry grain yields, ETc, and WUE from the automatic irrigation control plots were greater than or equivalent to those from the manual treatment plots when compared across the same irrigation level. Crop production functions were linear in 2009 for both methods of irrigation and curvilinear in 2010 as dry grain yields began to plateau between water application amounts delivered from irrigation treatments at the 55% and 80% levels. Results from this study indicate that both late and early maturing hybrids of grain sorghum are responsive to the TTT method of irrigation scheduling. Irrigation management with this algorithm can produce biomass, grain yields, and WUE levels that are similar to those managed with an accurate scientific irrigation scheduling method using the neutron probe.