Soil Water Hysteresis in Water-Stable Microaggregates as Affected by Organic Matter

Interaction of water and organic matter (OM) in pores affects the capacity for long-term C sequestration and water retention in soils. This study investigated the effects of the amount and distribution of OM in microstructures on water retention in soil microaggregates. The focus of the study was on the hysteretic soil water characteristic (i.e., the difference between the main drying and wetting curves), which has been largely ignored in previous studies on water-OM relations. The main drying and wetting branches of the water retention curve were measured using a water activity meter on water-stable microaggregates (53-250 μm), which were collected from surface soils (0-15 cm) subject to different management practices: tallgrass prairie restoration on a Mollisol, and tillage with and without N fertilization on an Alfisol. The results show that the presence of OM in