The effect of erosion, tillage, and winter cover crops on soil aggregate stability

This study was conducted to compare the effects of varying degree of erosion, tillage, and winter cover crops on soil structural stability. The study comparing degree of erosion was conducted at two field locations in Fayette County, TN, on a Memphis silt loam (fine-silty, mixed, thermic, Typic Hapludalfs) and a Grenada silt loam (fine-silty, mixed, thermic, Glossic Fragiudalfs). The comparison of tillage methods and cover crops was conducted at the West Tennessee Experiment Station, Jackson, TN, on a Lexington silt loam (fine-silty, mixed, thermic, Typic Paleudalfs). Soil samples were collected from four erosion phases at each site in Fayette County; slightly, moderately, severely, and very severely eroded. Tillage and winter cover crops effects on aggregate stability were determined by sampling long-term no-till and conventionally tilled corn, soybean, and cotton plots at the West Tennessee Experiment Station. To estimate the effects of cultivation and subsequent erosion on soil aggregate stability, the aggregate stability data from the erosion study, and the tillage and cover crop studies were contrasted with aggregate stability data from simulated tilled plots (mulch removed) from a virgin site located on a Grenada silt loam in Crocket County, TN. Aggregate stability of both the Memphis and Grenada sites was significantly different from the virgin site. The surface (0- to 2.5-cm) mean weight diameter for slightly eroded Memphis and Grenada was 0.258 and 0.957, respectively, compared to 1.059 for the virgin site. At the lower depth of both the Grenada and Memphis sites, aggregate stabilities are about the same among erosion phases. The differences in aggregate stability between Grenada and Memphis soil when compared to the virgin site resulted in part from the effect of erosion on soil surface properties. The soils from these two sites are high in silt, therefore highly erodible. The aggregates break down readily when wetted, and the particles are easily detached and transported. No-tillage produced significantly larger aggregates than the conventionally tilled plots. This significant difference is attributed to the loss of organic matter and disturbance of soil physical properties as a result of conventional tillage practices. Differences between the uneroded, cultivated and virgin site is partially due to loss of organic matter as a result of cultivation, as well as erosion.