This chapter describes ecological factors that affect agronomic performance and the environmental effectiveness of Conservation tillage (CT) in the United States Corn Belt. Agricultural sustainability of CT systems is assessed in terms of productivity and soil and environmental quality. The response of CT measured in terms of the criteria outlined above depends on several factors, including soil type, terrain characteristics, internal drainage, past land use history, climatic conditions during the growing season, and management systems used. The magnitude and the nature of tillage-induced alterations in these properties depend on antecedent conditions, inherent characteristics of soil, management systems, and climatic and ecological environments. Tillage systems' effects on soil temperature regime have been studied for several sites within the Corn Belt. Fertilization of most agronomic crops is generally restricted to the major nutrients of nitrogen, phosphorus and potassium and to the addition of limestone for correction of low soil pH. Soil densification and deterioration in soil tilth decrease the volume of macropores.