Soil tests do work! But some tests work beetter than others for Iowa soils. We want the best available for testing your samples. And you want to know what the soils on your farm need to give better results.
Monthey, L. G. and Cheney, H. B.
"Had Your Soil Tested?,"
Iowa Farm Science: Vol. 1
, Article 2.
Available at: https://lib.dr.iastate.edu/farmscience/vol1/iss7/2