Farmers growing corn and soybean in northwest Iowa have to consider the cost of ag lime when liming their soils. This is because of high limestone cost and the fact that the soils in northwest Iowa have high pH subsoil. The high pH subsoil moderates the potential negative effect on crop production from acid surface soil. Another factor that must be considered is the variable mixing of limestone into the soil with different tillage systems. The different amounts of soil mixing among no-tillage systems, ridge-tillage systems, and full-width tillage systems may affect the amount of limestone needed to correct soil pH and liming effect on crop yield.