What Does the Late-Spring Soil Test Really Measure?

The late-spring test for soil nitrate has been available in Iowa for about 10 years. Guidelines for using this test clearly indicate that the test measures concentrations of nitrate in the surface foot of soil when corn plants are 6 to 12 inches tall. Ongoing discussions concerning the reliability of the soil test, however, indicate uncertainty in what should be concluded from the soil nitrate concentrations measured