TILLAGE-INDUCED AND TRAFFIC-INDUCED CHANGES IN MACROPOROSITY AND MACROPORE CONTINUITY - AIR PERMEABILITY ASSESSMENT

Quantitative analysis of macropore geometry in undisturbed soils has been hindered by difficulties in creating conditions where macropore measurements can be separated from matrix pore measurements. Such analysis is important, however, for evaluating tillage management effects on both root growth and solute movement. Inferences regarding management effects on macroporosity were made possible by combining the use of improved air-permeability techniques with two recently developed methods to analyze air-permeability (K(a)) data, using undisturbed soil samples from a tillage study. Log10 K(a) values exhibited a near-normal distribution. In wheel-traffic interrows (Wh), macropore air permeability was significantly less under conventional-tillage corn (CT) than no-tillage corn (NT) and no-tillage alfalfa (ALF). Tillage differences were usually not significant in non-wheel-traffic interrows (NWh). Wheel traffic significantly decreased air permeability for CT, but not for NT or ALF. The two methods of analyzing air-permeability data yielded similar inferences regarding macropore geometry. Conventional tillage decreased bulk density (increasing total porosity) for NWh only, but seemed to decrease the stability, number, and continuity of macropores relative to NT and ALF. Macroporosity and macropore geometric factors were affected little by traffic for NT and ALF, but traffic significantly affected CT macropores in this study where samples were taken approximately 1 mo after corn planting.