Submitted to: American Society of Agricultural Engineers Meetings Papers
Publication Type: Proceedings
Publication Acceptance Date: August 31, 1997
Publication Date: N/A
Interpretive Summary: The site-specific application of irrigation water and fertilizer should offer opportunities to conserve water, to reduce the chance of either drought or flooding stress, and to reduce leaching of fertilizer or pesticides below the field in the areas subject to such losses. A center pivot irrigation system was modified to permit a range of water and chemical application rates to areas about the size of a 2-car garage. The water application system consisted of multiple segments 9.1 m long, each with three manifolds. Each manifold is controlled separately, allowing up to eight separate water application depths for any given speed of the system. The system is controlled by a computer using specialized software and soil, crop, and cultural information stored in a database. While the modified irrigation system was being developed and improved, it was used to apply water and nitrogen to a corn-soybean field experiment with regular plot boundaries in 1995 and 1996. Treatments in the experiment included irrigation, deep tillage, nitrogen application, and crop rotation. Irrigation increased corn yield over rainfall only both years and increased soybean yield one year. Yields for crop rotation and deep tillage were not different. Deep tillage increased corn yield with irrigation but not with rainfall only. The irrigation control system was improved and its reliability increased during the experiment.
Technical Abstract: Research suggests spatial variability in yield for the southeastern Coastal Plain may be caused primarily by water relations. This causes difficulties in scheduling irrigation for conventional center pivots. Thus, we designed and constructed a site-specific center pivot irrigation system that could independently apply variable rates of water and chemicals to 100-m**2 areas within the irrigation system. A commercial center pivot was modified by adding three 9.1-m manifolds in 13 segments along the truss. Manifolds and nozzles were sized to provide 0 to 7x the minimum rate, which was 12.7 mm in 1.8-mm increments, when traveling at half speed. A computer-controlled management system obtained the position from the center pivot controller and switched on the appropriate valves to obtain the application rate for a specific area. During 1995 and 1996, the system was used for water and nitrogen applications in a fixed-boundary ycorn-soybean field experiment with irrigation, deep tillage, nitrogen, and crop rotation treatments. Irrigation increased corn yield over rainfall only in both years and increased soybean yield one year. Yields for crop rotation, nitrogen application, and deep tillage were not different. Deep tillage increased corn yield with irrigation but not with rainfall only. The modified center pivot system applied water and nutrient satisfactorily to individual plots and system performance and reliability improved during the two-year period.