Using a GPS when fertilizing the fields

By Gary Sliworksy
OMAFRA Rep.

For the past several decades, most producers have applied fertilizer based on a specific crop yield goal for each field, but today some farmers are varying the amount of fertilizer applied across their fields.
Producers now can use the global positioning system (GPS), coupled with other technologies, to refine their crop fertility practices. Instead of applying a uniform fertilizer rate throughout a field, producers are experimenting with spatial management practices by varying yield goals within fields using GPS and variable-rate application equipment.
These farmers are attempting to make more efficient use of the fertilizer applied to each field by dividing fields into management zones. However, producers have to decide which factors to use in developing variable rates.
Traditional fertilizer recommendations are based on analysis of a composite soil sample taken from several locations across the field. Producers experimenting with varying the fertilizer application are incorporating information from a variety of sources.
Management zones are made using geographic information system (GIS) computer programs to combine information from soil survey maps, GPS-marked soil tests, variable soil properties across a field, the previous year’s satellite imagery, aerial photographs and crop yield data. The zones are assigned yield goals. Farmers can refine their fertilizer recommendations by soil testing each zone.
One of the problems facing producers who want to use spatial management practices in crop production is how to combine information to develop management zones, and then make variable-rate application maps (often called prescription maps) that can be used in their fertilizer application controllers. This process requires a computer GIS program and the skills to use it. Some fertilizer supply companies sell this service on a per-acre basis.
Several GIS computer programs are available to make variable-rate application maps, including general GIS programs such as ArcView, MapInfo and Farm Works. Most of the major agricultural equipment companies sell GIS programs.
Not all GIS programs are capable of handling image data or able to export maps to use in variable-rate application equipment, so it is important to evaluate GIS software before purchasing it.