Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 5, 1997
Publication Date: N/A
Interpretive Summary: Patches of sandy or clayey soils can cause big differences in crop yield from area to area in the same field. These differences are the reason for current interest in precision farming, in which fertilizer, pesticides, plant population, or irrigation is customized for the soil at a specific place in the field rather than applied uniformly over the entire field. The site-specific application of irrigation water 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 sensitive areas. A center pivot irrigation system was modified to permit a range of water and chemical application rates to areas about 10 m on a side. The water application system consisted of multiple segments 9.1 m long, each with three manifolds. Each manifold was controlled separately, allowing up to eight separate water application depths for any given speed of the system. A computer controls the system using specialized software and soil, crop, and cultural information stored in a database. The modified system successfully applied water and nitrogen to a field experiment in 1995. Future work will include improved system reliability and installation of both a pesticide application system and sensors for measurement of crop status. A second center pivot will also be modified to allow variable applications to highly-variable soils with irregular boundaries.
Technical Abstract: Spatial yields since 1985 in a corn-wheat-soybean rotation at Florence, SC show little correlation of yield data with expected yields for soil map units. Research suggests spatial variability in yield for the SE 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-sq m areas within the irrigation system. A commercial center pivot was modified by adding three 9.1-m manifolds in 13 segments along the truss. Nozzles were spaced 1.5 m (5 ft) apart along each manifold, and both manifolds and nozzles were sized to provide 1x, 2x, and 4x of a minimum application rate at a given tower speed. All combinations of the three manifolds provided up to 7x the minimum rate, which was 12.5 mm, when traveling at half speed. A programmable controller installed on the moving portion of the center pivot obtained the position from the center pivot controller and opened the appropriate valves to obtain the application rate for a specific area. During 1995, the system operated acceptably for a fixed-boundary field experiment. Experience gained with this system will be used to modify a second commercial center pivot for site-specific water, nutrient, and pesticide management on a site with soil variation (irregular boundaries) typical of Coastal Plain fields.