This phase of soil testing consists of the laboratory functions. It is a highly technical area where precision laboratory instruments and chemical procedures are used for soil analysis. In soil testing programs, the chemical procedures must be reliable, suitably accurate, and provide useful information. Most, but not all, laboratories are part of a quality assurance program that sends out test samples. If a laboratory produces results that vary greatly from the average, then the laboratory must investigate its procedures to make sure they are being followed correctly. Each chemical test has a different range of variability. For example, pH readings don’t vary greatly, but sulfur readings will.
Decisions must be made to determine which nutrients or soil properties should be assessed by chemical procedures. The main objective of chemical analysis is to predict sites where applying nutrients will increase yields. Zinc, copper, boron, sulfur, or chlorine analysis on all soils from Nebraska fields will not always provide information useful in deciding which fertilizer nutrients may be needed. It is reasonable not to assess all nutrients on every sample when a particular nutrient is known to be well supplied by the soil or that a specific crop does not respond to additional fertilizer application even when soil test results are low.