Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/12/2006
Publication Date: 4/5/2007
Citation: Blanco-Canqui, H., Lal, R., Shipitalo, M.J. 2007. Aggregate disintegration and wettability for long-term management systems in the Northern Appalachians. Soil Science Society of America Journal. 71(3):759-765. Interpretive Summary: When soil aggregates are stronger and less wettable the soil is less prone to erosion. Crop production practices such as reduced tillage and addition of crop residues and animal manures can increase aggregate strength and reduce wettability by increasing soil organic matter content. In this study, we measured aggregate strength and wettability for one soil type under a variety of long-term soil management practices to determine their affect on these properties. We also measured soil organic matter content, penetration resistance, and shear strength to determine if these properties could be used to predict aggregate strength, wettability, and resistance to erosion. We found that soil under forest vegetation had the strongest, least wettable, aggregates while soil that was moldboard plowed had the weakest, most wettable, aggregates. Of the crop production practices investigated, the strongest, least erodible, aggregates were noted when corn was produced using no-till and animal manure was added on an annual basis. Soil penetration resistance and shear strength are easy to measure and were mathematically related to aggregate strength and soil erosion and may be useful in predicting these properties in other soil types. Farmers can conserve soil and improve soil quality by adopting no-till crop production practices, especially if animal manure is used as a soil amendment.
Technical Abstract: Assessment of structural properties of discrete soil aggregates is fundamental to understanding soil erosional processes. Management-induced changes in soil organic carbon (SOC) concentration may significantly alter aggregate properties. Thus, the detachment and wetting characteristics of individual aggregates were determined for a Rayne silt loam (fine-loamy, mixed, mesic Typic Hapludult) under contrasting scenarios of long-term (>22 yr) moldboard plow (MP), no-till with (NTm) and without manure (NT), pasture, and forest systems in the northern Appalachian region. Relationships of aggregate detachment with other soil properties such as aggregate density, cone index (CI), shear strength (SHEAR), and SOC concentration were also studied. Aggregate detachment was assessed based on the kinetic energy (KE) of simulated raindrops required to detach 1- to 8-mm aggregates at -0.01, -0.1, -1, and -154 MPa potentials. Management affected the aggregate resistance to the erosive energy of raindrops (P<0.01). Aggregates from forest soils required the highest KE (>50 ergs) for disruption and those from MP soils required the lowest (<19 ergs). At the -0.01 MPa potential, the KE needed to disintegrate aggregates in NTm was about 3 times higher than that for the NT, indicating that manuring improved aggregate stability. Water drop penetration time (WDPT) showed that aggregates from agricultural practices had a very low water repellency (WDPT<10s), but those from forest management had some water repellency (WDPT>10s) in the 0- to 20-cm soil depth. About 91% of the variability in soil loss was explained by aggregate detachment and 58% by aggregate wetting. The SOC concentration explained 48% of the variability in detachment and 86% of wetting of aggregates. The CI and SHEAR were potential predictors of aggregate detachment, explaining about 81% of its variability. Long-term management altered aggregate detachment, but its effects on aggregate wetting within agricultural practices were small.