The accuracy of a soil test result can be affected by both the laboratory analysis and the quality of the soil sample. A soil sample that is not representative of the corresponding field area will likely be misleading and cause inappropriate fertilizer application rates. Therefore, it is essential that each field be sampled using procedures that represent the majority of the soils in the field. Preferably, areas with significant variations in soil texture, color, topography, and cropping and fertilization history should be sampled and fertilized separately from the rest of the field.

For specific details on soil sampling, please see University of Wisconsin Extension publication A2100 - "Sampling Soils for Testing".

Pre-season soil tests provide critical information to determine the amount of residual nutrients available. In-season soil analysis is an additional tool to monitor nutrient availability and complement petiole analysis. Crop consultants have found in-season soil tests can predict potentially limiting soil nutrients which can be adjusted prior to significant drop in petiole concentrations (Lang and Stevens, 1997).