TOPSOIL DEPTH AND DESURFACING EFFECTS ON PROPERTIES AND PRODUCTIVITY OF A TYPIC ARGIUSTOLL

Information from desurfacing studies has been used to develop simulation models for assessing soil erosion-productivity relationships. No attempt has been made, however, to directly compare the effect of desurfacing on soil properties and crop production with differences in topsoil depth arising from erosion or slower soil development. The objectives of this study were to determine the effects of topsoil depth on soil properties and continuous corn (Zea mays L.) yield for both a desurfaced summit and adjacent eroded backslope sites on a Beadle clay loam (fine, montmorillonitic, mesic Typic Argiustoll). Field studies were conducted for a 5-yr period. Plots were established on a backslope position consisting of three topsoil-depth classes (E1, E2, and E3). Plots were also established on an adjacent summit position consisting of three desurfaced classes (0, 30, and 45 cm of topsoil were removed in 1965). Prediction equations were developed from 16 variables. The selected equation, with three variables, explained 49% of the variability in grain yield. Depth to middle of the Bk horizon was the most important of the independent variables, explaining 23% of the yield variability, followed by soil water use, and the interaction of water use with depth to middle of the Bk. The equations for the desurfaced summit and eroded backslope plots were significantly different. A reduction in topsoil depth reduced yield more on the desurfaced summit compared with the eroded backslope. This effect was primarily a result of disproportionately higher yield potentials for the summit control plots due to landscape position and soil formation.