Farmers growing corn and soybeans in northwest Iowa have to consider the cost of ag lime when liming their soils. This is because of high limestone costs and the fact that the soils in northwest Iowa have high pH subsoil. The high pH subsoil moderates the negative effect of acid surface soils. 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 between no-till systems, ridge-till systems, and conventional tillage systems may affect the amount of limestone needed to correct the soil pH and crop yields.