Submitted to: Decennial National Irrigation Symposium
Publication Type: Proceedings
Publication Acceptance Date: 9/17/2010
Publication Date: 12/5/2010
Citation: Thompson, A.L., Sudduth, K.A., Henggeler, J.C., Vories, E.D., Rackers, A.D. 2010. Variable Rate Irrigation Management for Humid Climates Using a Conventional Center Pivot System. Decennial National Irrigation Symposium, December 5-8, 2010, Phoenix, Arizona. IRR10-9849. Interpretive Summary: Soil textural variability within irrigated fields diminishes the effectiveness of conventional, single-rate irrigation with respect to uniformity, scheduling, and water use efficiency. This may contribute to a lack of interest or commitment by producers to irrigation scheduling even though, in general, irrigation scheduling has shown a significant increase in gross profits. Commercial center pivot irrigation systems that can address texture variability by applying water at a spatially-variable rate are available but expensive. As a lower-cost alternative, the rotational speed of a conventional center pivot irrigation system with a computer control panel can be changed depending on azimuth to spatially vary application depth in wedge-shaped sectors. Such an approach can address some, but not all, of the texture variability present depending on its spatial pattern. In this study, we implemented such sector-based control for corn production on a field in Southeast Missouri where the texture varied from under 20% to over 90% sand. We found that applying 0.6 in. of water per irrigation was the most efficient overall, while 1.2 in. of water per irrigation was better for areas with lower sand content. These results showed the benefit of varying irrigation amount based on soil texture and encourage development of methods for sector-based variable-rate irrigation using conventional center pivot systems. If such methods are proven, they may result in water savings and increased profits for crop producers.
Technical Abstract: This study investigates suitability of a standard commercial center pivot system for variable-rate water application under Mid-South conditions. The objective was to determine if field variability data can be applied to conventional moving sprinkler systems to optimize irrigation management on non-uniform soils. Data were collected using a three tower pivot with overhead spray nozzles located at the University of Missouri Delta Center. Treatments include rainfed and irrigation sets of 8 to 46 mm in approximately 8 mm increments with total annual irrigation depth less than 190 mm. Irrigation scheduling was based on the Arkansas Scheduler method. Corn yields and IWUE are presented for all treatments for the first year of study. Soil texture varied from less than 20% to greater than 90% sand in the same field. Data were analyzed using Proc-GLM for yield by treatment and texture based on over 2400 averaged yield monitor observations. Although rainfall was timely throughout the growing season, irrigated yields were significantly greater than rainfed (Pr >95%) for all treatments. Average yields were greatest for soils with percent sand between 46 and 62% with lowest average yields for soil textures greater than 74% sand. The greatest average yield over all texture classes was for an application depth per set of 15 mm. Increased irrigation depth per set (31 mm and greater) favored heavier textured soils (i.e. low sand content). Soil textures on either extreme were more problematic for irrigation scheduling, with the highest sand content being the most sensitive.