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Title: MECHANICAL PROPERTIES AND ORGANIC CARBON OF SOIL AGGREGATES IN THE NORTHERN APPALACHIANS

Author
item BLANCO-CANQUI, H - OHIO STATE UNIV.
item LAL, R - OHIO STATE UNIV.
item Owens, Lloyd
item POST, W - OAK RIDGE NATIONAL LAB
item IZAURRALDE, R - UNIV. OF MARYLAND

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/18/2005
Publication Date: 9/12/2005
Citation: Blanco-Canqui, H., Lal, R., Owens, L.B., Post, W.M., Izaurralde, R.C. 2005. Mechanical properties and organic carbon of soil aggregates in the Northern Appalachians. Soil Science Society of America Journal. 69:1472-1481.

Interpretive Summary: Soil is comprised of small particles and aggregates of small particles. The properties and behavior of the 'macro-scale' soil depends on the properties of these individual aggregates, i.e. 'micro-scale'. Processes that are most vital to root penetration and growth, seedling emergence, water and air flow, and biological activity occur at a micro-scale soil structural level. Frequently soil properties are determined for the macro-scale, and little is know about micro-scale soil properties. The purpose of this study was to determine how long-term (greater than 15 years) management practices influence these properties. Included in the management practices that were evaluated were conventional tillage, chisel plow, no-till with manure, no-till without manure, and forest. Aggregates from the forest had the lowest tensile strength and the highest organic carbon. Aggregates from the conventional tillage and chisel plow had the highest tensile strength and the lowest organic carbon. Manure applications had a positive impact on properties of soil aggregates such as increasing organic carbon content and improving soil moisture retention. Excessive tillage and rapid post-tillage consolidation had negative impacts such as low organic carbon content and high tensile strength. Higher soil organic carbon reduced aggregate bulk density. Long-term land use and management practices caused significant changes in the properties of soil properties, beginning at the micro-scale. These results are important to other scientists and management planners in helping them to understand how selected management practices may enhance soil properties and subsequent plant growth.

Technical Abstract: Aggregate properties determine the macro-scale structural condition of the soil. However, soil properties are ordinarily measured on bulk soil rather than on discrete aggregates, and thus data on aggregate properties are limited. This study assessed the mechanical properties of soil aggregates and their relationships with soil organic carbon (SOC) content for long-term (>15 yr) conventional tillage (CT), chisel plow (CP), disk with manure (DM), no-till with manure (NTM), no-till without manure (NT), pasture, and forest management practices in the North Appalachian region. Tensile strength (TS), aggregate bulk density, soil moisture retention (SMR), and SOC content were determined on soil aggregates (1-8 mm) for 0-10, 10-20, and 20-30 cm depths. Aggregates from forest had the lowest TS (63 kPa) and aggregate bulk density (0.99 Mg m-3) and the highest SOC content (70 g kg-1), whereas the CT and CP treatments had the highest TS (~358 kPa) and the lowest SOC content (14 g kg-1) for 0-10 cm (P<0.01). The TS and SMR (0 to -333 kPa) in NTM were about 1.8 times higher than the average of CT and CP. The SOC content for NTM was 3.4 times higher than the average of CT and CP and 2.2 times higher than that for NT. The aggregate bulk density was 1.35 Mg m-3 in NTM and ~1.61 Mg m-3 in CT and CP. Manuring had a positive and excessive tillage negative impact on properties of soil aggregates. Mean aggregate bulk density was significantly higher than the density of bulk soil. Increase in SOC content reduced aggregate bulk density and TS and increased SMR (0 to -10 kPa). The log-transformed TS (LogTS) increased with increasing aggregate bulk density and decreased with increasing aggregate size. Size, SOC content, and aggregate bulk density explained about 84% of the variability of LogTS of aggregates using pedotransfer functions (PTFs). Long-term land use and management practices caused significant changes in the properties of soil properties.