Back to Contents4.1 Previous Work
Traditional methods of fertilizer and chemical application tend to treat all areas of a field similarly, regardless of any variation that may occur within that field. With the traditional approach, soil cores are obtained at random throughout a field to form a composite. These samples are sent to a laboratory for chemical analysis, and a single nutrient recommendation is made for each field. Nutrients (nitrogen, phosphorus and/or potassium) are then applied in a broadcast fashion to the entire field. Prior to the development of precision agriculture, within field variability was accepted as a factor over which a producer had little control. In fact, this variability was used to justify increased recommended fertilizer application rates to insure crop yield was not limited. Anderson and Bullock (1998) suggest that variable-rate nutrient application is more likely to be useful in fields with areas of low soil fertility.
Searcy (1995) defined site-specific crop management as "the use of local soil and crop parameters to make precise application of production inputs to small areas with similar characteristics." In the concept of site-specific management, spatial variability occurs across the relevant parameters including soil type, fertility, slope and microclimate etc., which affect crop production. Today, production inputs (fertilizer or seed) can be varied as a function of location in a field using Variable-Rate Technologies (VRT). Site-specific management is a comprehensive program that utilizes a combination of intensive soil sampling, digital field maps, computers, GPS, and variable rate applications.