Submitted to: European Conference on Precision Agriculture Proceedings
Publication Type: Proceedings
Publication Acceptance Date: May 15, 1997
Publication Date: N/A
Interpretive Summary: Airplane passengers can easily see variation in soils in the Southeastern Coastal Plain, especially during periods when the soil is clean after tillage. Fields throughout the region are dotted with Carolina Bays, which are shallow, circular depressions of varying sizes and debated origin. Farmers growing crops in such fields must choose seeding, fertilizer, and pesticide rates, but optimum rates are not usually the same for each soil. The emerging technology of precision agriculture allows site-specific adjustments to equipment. For example, nitrogen rate can be adjusted to match needs for a particular spot rather than applied uniformly to the whole field. In the Southeastern Coastal Plain, water stress appears to be an important cause of yield variation. Therefore, the USDA-ARS in Florence, SC, built a site-specific center pivot to adjust irrigation, fertilizer, and pesticide amounts for varying soils. Initial testing has been done on a conventional small-plot experiment, where different rates of irrigation and fertilizer were applied to each plot. The first two years of tests indicate that the machine works as planned, thus proving technical feasibility of site-specific irrigation on variable soils. Research planned with the new machine will determine the parameters that must be adjusted to overcome soil variability.
Technical Abstract: Yield maps from 1985 to present on a highly variable Coastal Plain field increasingly implicate soil water relations as the cause of spatial yield variation. Soils are sandy, often with dense horizons. Together, these factors limit water storage in the root zone, a conclusion reached through experience, observation, and process-level crop modeling. Management of water through irrigation in this region is complicated by the limited soil water storage and the significant chance of rain, which increases risk of NO3- leaching if deficit irrigation is not practiced. However, spatially variable soils mean that even careful management of water, if done uniformly across the field, will still be improperly done on a significant portion of the area. It appears that the only method to address water stress on spatially variable fields while minimizing the potential of leaching under wetter areas is by site-specific water management. Therefore, in 1995, two site-specific center pivots were built by adding custom hardware to commercial center pivots. The first machine was used to control water and fertilizer application for a replicated experiment with 144 small plots (9 m radially x 7.5 degrees [10-15 m]), which tested the hardware and software under controlled conditions. The second machine is undergoing modifications at the current time.