Studies of Spatial Patterns of Soil Redistribution In Two Small Agricultural Fields

Studies of the redistribution patterns of soil within a field or watershed are limited. Our studies focus on understanding patterns of soil movement and redeposition within two small agricultural fields (12-15 ha) in the Des Moines lobe till plain of Iowa. Our studies investigated the relationship between soil redistribution, soil organic carbon (SOC), and geomorphology in these agricultural fields. Cesium-137 was used to estimate soil redistribution patterns. Soil redistribution was related to landscape position and shape. Soil loss increased as gradient slope increased. Soils on concave slopes showed deposition and higher SOC than soils on convex slopes. These data suggest that soil redistribution patterns and topographic patterns can be used to help understand soil and SOC redistribution patterns on agricultural landscapes. The strong significant relationships between the patterns of soil and SOC redistribution in these agricultural fields suggest that they are moving along similar physical pathways. This study also indicates that landscape geomorphology is a key factor for understanding soil and SOC movement and redistribution within a field or watershed. It is often assumed that eroding soils results in soil losses from agricultural fields; however, our studies indicate that most of the eroding soils are subsequent redeposited within same field. An important implication of this study is that sediment yield from a field may have little to do with actual rates of soil erosion (soil redistribution) patterns occurring within the field. Our studies indicate that even though the net soil loss from the fields was negligible, there was soil erosion over much of the fields. Hillslopes have been eroding over the past 40 years and have been redeposited in low areas.