Plant response to topsoil thickness on an eroded loess soil

Topsoil was added to an exposed C horizon of a loess soil in northeastern Nebraska in thicknesses of 0, 100, and 200 mm. The field was planted to dryland corn the first year, oats the second year, and corn the third and fourth years. Corn grain yield was significantly greater on the 100-mm and 200-mm topsoil treatments than with no topsoil; 200 mm of topsoil was required to increase oat grain yield. Total dry-matter production of oats generally was greater with the 100-mm and 200-mm treatments than with no topsoil on four sampling dates during the growing season. Yield of corn and subsequent oat grain was not affected by adding 112 kg/ha of N over the base application of 34, 10, 10, and 7 kg/ha of N, P, K, and S, respectively, prior to the first corn crop. N concentrations in the oat plant and grain were not affected by topsoil thickness. Results indicate there are characteristics of topsoil beneficial to plant growth that, once gone, cannot be readily replaced simply by adding fertilizer.