Effects of agriculture on the classification of Black soils in the Midwestern United States

Abstract

Veenstra, J. J. and Burras, C. L. 2012. Effects of agriculture on the classification of Black soils in the Midwestern United States. Can. J. Soil Sci. 92: 403–411. Soil surveys are generally treated as static documents. Many soil survey users assume that pedon data generated 30 to 50 yr ago still represents today's soil, as short-term changes in soil properties are perceived to be limited to the soil surface and thus pedologically insignificant. In this study, we re-sampled and re-analyzed 82 pedons with historical descriptions and laboratory data in Iowa, United States, to evaluate changes in soil profile properties and taxonomic classification after approximately 50 yr of agricultural land use. Using historical and current data, we classified sampled pedons using Canadian Soil Taxonomy, US Soil Taxonomy and the Food and Agriculture Association World Reference Base (FAO-WRB). Our results show that soil characteristics have changed significantly enough to change the classification. In each taxonomic system, the classification of 60% or more of the sampled pedons differed from the original. Classification of 15 to 32% of the sampled pedons changed at the Order (or equivalent) level with 11 to 33% of the pedons originally classified as Black soils – Mollisols, Chernozems or Phaeozems – no longer classified as Black soils. The change in soil classification over such a short-time period challenges the validity and usefulness of treating existing soil maps as static documents as well as traditional soil classification hierarchies.