Saturated Hydraulic Conductivity and Porosity within Macroaggregates Modified by Tillage

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 ( K s ) 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 K s. 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 K s within macroaggregates, of the same size fraction, from both the Hoytville silty clay loam and Wooster silt loam soil types. Values for K s of NF aggregates, 5.0 × 10 −5 cm s −1 , were reduced 50‐fold by long‐term CT treatments of the Hoytville series. The K s values through Wooster aggregates from NF, 16.0 × 10 −5 cm s −1 , were reduced 80‐fold by long‐term CT treatments. The K s values through NF and NT aggregates were positively correlated with their intraaggregate porosities ( R 2 = 0.84 for NF and R 2 = 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.