The use of GPS allows soil sample sites to be accurately located within a field and fertility levels mapped. This technology also allows yield samples to be taken from accurately located positions and then compared to soil test results. Using this technology, producers can pinpoint locations of significant soil variability. Researchers have reported that a constant rate of nitrogen application based on a composite sample of a field resulted in over fertilization of areas with high levels of nitrogen and under fertilization of areas with low levels of available nitrogen. Variable fertilizer levels in potato fields affect quality as well as yields.
Excessive nitrogen reduces the dry matter of potatoes and processing quality.
Variability of dry matter is a concern to potato processors who strive for maximum uniformity of product to meet the needs of global markets. The project also evaluated the usefulness of GPS as a tool for intensive grid sampling. The field was selected because of its variability in topography and soil types. The east half of the quarter-section pivot was planted to potatoes. A 40-acre portion in the north part of the potato field was selected for the demonstration.