These differences are the reason for current interest in site-specific crop management, 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. Most development in the site-specific farming area has been for spreading fertilizer. 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 the areas subject to such losses. The system is controlled by a computer using specialized software and soil, crop, and cultural information stored in a database. The modified application system has been used to apply water and nitrogen to a field experiment with fixed, regular plot boundaries since 1995.
Preliminary measurements show acceptable water and nutrient application uniformity.
Current work includes improvements to make the system to make it more reliable and to accommodate irregular-shaped areas of variation. A second center pivot will be modified to allow variable applications to highly-variable soils with irregular boundaries. The schematic diagram illustrates a technique for implementing variable rate control on irregular-shaped areas using the control units available on the modified center pivots.