What can I test soil for?

The routine soil testing program for laboratories using the Wisconsin soil test recommendation program includes soil pH, organic matter content, lime requirement (buffer pH), and extractable phosphorus (P) and potassium (K). In addition, special tests may be requested for nitrate-nitrogen, calcium, magnesium, sulfur, boron, manganese, and zinc. Soil tests for copper, iron, molybdenum, and chlorine have not been calibrated to crop response in Wisconsin; these nutrients are rarely deficient in Wisconsin soils. 

Several other tests can be performed on request. These tests include physical analysis for particle size distribution (% sand, % silt, % clay), exchangeable sodium, soluble salts, total nitrogen, inorganic nitrogen, total organic carbon, and heavy metals (arsenic, cadmium, chromium, cobalt, copper, iron, lead, manganese, molybdenum, nickel, selenium, zinc). 

Where can I test soils in Wisconsin?

In Wisconsin, a soil testing laboratory must be certified by the Wisconsin Department of Agriculture, Trade, and Consumer Protection (WDATCP) if results are to be used in nutrient management planning or related to any government cost-sharing program.

A current list of the Wisconsin certified laboratories can be found here.

Table 3.1 briefly describes the procedures used for each soil test performed at University of Wisconsin laboratories and other WDATCP-approved laboratories. 

Table 3.1 – Analytical procedures for soil tests performed at University of Wisconsin laboratories and Wisconsin DATCP-approved private laboratories

How to account for soil test result variability

To maintain certification in Wisconsin, a WDATCP-certified laboratory is required to meet specific analytical quality standards. However, with any soil test there is a level of inherent variability that can be expected both within a lab and between certified laboratories. The variability within a lab should be lower than between labs.

In general, soil pH and Sikora buffer pH results should be within 0.2 pH units when the results of two laboratories are compared. Soil test levels for P and K should be within 10% of the “true value.” For example, a soil with 20 ppm P should test in the range of 18–22 ppm when run by different certified labs, and a soil with 100 ppm K should test in the range of 90–110 ppm.