The consequences of homogenous treatments of agricutlural fields is investigated and quantified for several farm scale test sites throughout Alberta. A series of integrated data collection systems using GPS to locate and map information such as salinity and yield are discussed in stages of design, software, hardware and implementation. Results from the spatial data analysis produced a prescription map describing the fertilizer inputs for specified regions of the field. To fulfill the variable input requirements, a real time differential GPS system integrated with a variable rate air seeder was designed and implemented at each of the test sites. The theory and preformance of the GPS equipment and techniques used to verify the accuracy and repeatability of the derived positions are discussed and results from analysis software developed are presented.