Management-induced aggregation and organic carbon concentrations in the surface layer of a Torrertic Paleustoll

Abstract

Soil organic carbon concentrations (OCCs) decline when semiarid grasslands are brought under cultivation. As a result, soil aggregate size and stability may decline, which, with the decreases in OCC, may degrade soil quality and reduce crop yields. Effects of cropping systems, crop or field conditions, and tillage methods on dry and water-stable aggregation and OCCs in the surface layer of a Torrertic Paleustoll (Pullman clay loam) were determined. Samples were obtained from the 0–3-cm depth in plots of four dryland studies and three non-replicated field areas. Areas sampled ranged from those cropped to winter wheat ( Triticum aestivum L.) and grain sorghum ( Sorghum bicolor (L.) Moench) for over 20 years to grasslands converted to cropland in 1994. In general, soil aggregates were smaller and OCCs were greater with no-tillage (NT) than with stubble mulch tillage (SMT) on areas cropped for over 20 years. On areas recently converted to cropland, aggregates were larger and OCCs were greater with NT than with other tillage methods. The 0.42–0.84- and 0.84–2.0-mm dry aggregates were among those most stable when sieved in water. The results indicate practices that maintain soil OCCs at the higher levels and promote development of dry aggregates in the 0.42–2.0-mm size range are important for production sustainability of Torrertic Paleustolls such as Pullman clay loam and similar soils.