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Department of Crop and Soil Sciences, Michigan State University, East Lansing, MI 48824
* Corresponding author (smucker{at}msu.edu).
Greater knowledge of intraaggregate porosity modifications by tillage conveys new information for identifying additional hydrologic, ion retention, and aggregate stability responses to specific management practices. Macroaggregates, 2 to 4, 4 to 6.3, and 6.3 to 9.5 mm across, were separated into multiple concentric layers and their porosities were determined. Saturated hydraulic conductivity (Ks) of multiple aggregate fractions from two soil types subjected to conventional tillage (CT), no tillage (NT), and native forest (NF) soils were measured individually to identify the effects of tillage on aggregate structure, porosity, and Ks. Intraaggregate porosities were the highest in NF aggregates. Greater porosities were identified in exterior layers of soil aggregates from all treatments. Lowest intraaggregate porosities were observed in the central regions of CT aggregates. Soil aggregates, 6.3 to 9.5 mm across, had the greatest total porosities, averaging 37.5% for both soil types. Long-term CT reduced intraaggregate porosities and Ks within macroaggregates, of the same size fraction, from both the Hoytville silty clay loam and Wooster silt loam soil types. Values for Ks of NF aggregates, 5.0 x 10–5 cm s–1, were reduced 50-fold by long-term CT treatments of the Hoytville series. The Ks values through Wooster aggregates from NF, 16.0 x 10–5 cm s–1, were reduced 80-fold by long-term CT treatments. The Ks values through NF and NT aggregates were positively correlated with their intraaggregate porosities (R2 = 0.84 for NF and R2 = 0.45 for NT at P < 0.005). Additional studies are needed to identify rates at which pore geometries within macroaggregates are degraded by CT or improved by NT.
Abbreviations: CT, conventional tillage • Ks, saturated hydraulic conductivity • NF, native forest • NT, no tillage
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