Anion Leaching in Two Kentucky Soils under Conventional Tillage and a Killed‐sod Mulch1

Abstract

This study was established to determine the reasons for the larger losses of nitrogen under corn grown in killed sod as compared to conventionally tilled corn. No crop was grown. Two soils, Maury silt loam, a well‐drained soil with rapid permeability and Lowell silty clay loam, a well‐drained soil with slow permeability, were used. Chloride was used as a tracer for nitrate since it is little affected biologically. Soils were sampled by hand using a soil tube periodically to a depth of 90 cm in 15 cm increments so that both nitrate and chloride could be determined. Differences between distributions of nitrate and chloride were ascribed to mineralization and/or denitrification.On the Maury silt loam (Typic Paleudalfs, fine, mixed, mesic), no evidence of denitrification was found. Mineralization of nitrate was high and no leaching of chloride or nitrate occurred under conventional tillage during the growing season. Under the killed sod, mineralization was lower and leaching was appreciable during the growing season. During the following winter, leaching was similar on both tillage treatments, but because of the differences in leaching during the growing season, essentially all of the chloride and nitrate were removed from the 90 cm profile under the killed sod and only about half from conventionally tilled soil by the following April.On Lowell silty clay loam (Typic Hapudalfs, fine, mixed, mesic) there was similar behavior during the growing season except that some leaching occurred even on the conventionally tilled soil and denitrification apparently occurred under both tillage treatments at the depth where organic matter was highest.The results suggest that, during the growing season, nitrate losses by leaching and a lower rate of mineralization are responsible for the lower yields of corn observed with low nitrogen rates under a killed‐sod mulch. Rates of nitrate and chloride movement during the winter were about the same under both conventional tillage and killedsod mulch.