Hydric soil indicators in mollisol landscapes

Mollisols are mineral soils that usually develop under prairie vegetation. They are characterized by relatively thick, dark surface horizons resulting from an increased organic matter content (McDaniel et al. 2011), which can present problems for hydric soil identification due to the lack of visible iron-based redoximorphic features (Chapters 7 and 8) in the upper part of the soil profile. This chapter discusses some of the potential problems encountered when delineating hydric soils in Mollisol landscapes and describes specific hydric soil indicators developed for use in delineating hydric Mollisols. The thick accumulations of organic matter associated with Mollisols are primarily due to the prairie grass vegetation, which has a dense fibrous root system. The roots, which proliferate in the soil even to depths of 75 cm or greater, have a high rate of annual turnover (Dahlman and Kucera 1965). Because a significant portion of the vegetation biomass is within the soil, root exudates and root turnover readily contribute substantial organic matter to the upper portions of these soils. When the grassland vegetation is disturbed by grazing or fire, the copious, fibrous roots of prairie grasses and the roots of leguminous forbs create abundant “ligno-protein” molecules of soil organic matter that resist oxidation and solution (Hole and Nielsen 1970). The presence of abundant Ca stabilizes organic matter and darkens the soil, creating the characteristic deep black soil characteristic of grassland soils (Mollisols) in temperate regions worldwide. Mollisols, however, can also form under forest vegetation. These soils usually are associated with wetter soil environments CONTENTS