Conventional vs. Variable Rate


In the fall 2014, MKC pulled a typical composite sample on a field for a grower. After reviewing the soil test results with an MKC field marketer, the grower decided to pursue a grid sample on the field. The composite sample showed a pH of 5.2 but the grid samples revealed the pH was anywhere from 5.0 to 7.9. The composite sample showed a phosphorus level of 24ppm while the grids revealed it to be anywhere from 17 to 60ppm. These sample results display the common variability on most fields that are far from the ideal pH range of 6.5 and 30-35ppm phosphorus for most crops.

On the lime alone, comparing the recommendations between the composite sample and the grid sample would have resulted in only 3% of the acres receiving the correct application rate of lime. The grid results also showed 11 acres of the field did not need lime applied which saved the grower $1,105.50. Ultimately, the savings paid for the grid sample testing. Similar savings and results were found with the VRT phosphorus application.