Comparison of Morphology and Porosity of a Soil Under Conventional and Zero Tillage

Effects of tillage on soil morphology and porosity were investigated in plots planted to corn (Zea mays L.) for seven consecutive years. Micromorphometric analyses indicated that Ap horizons of no-till plots had approximately half the macroporosity (pores ≥ 200 μm equivalent circular diameter) of those of conventionally tilled plots. Loss of macroporosity was characterized by a decrease in mean pore size and a tendency for pores to become elongated, less tortuous, and oriented parallel to the soil surface. Obvious zoological activity, which consisted mainly of burrowing earthworms, resulted in two to nine times more bioporosity in a no-till pedon than in a conventionally tilled pedon. Earthworm activity also contributed to the formation of 5-cm-thick B & A horizon and a more uniform distribution of organic carbon than in the conventionally tilled pedon. These differences in morphology are reflected in the classification under Soil Taxonomy but not under the Canadian System. We speculate that zoological activity may serve to counteract the reduction in macroporosity in the Ap of the no-till pedon. Key words: Bioporosity, earthworms, micromorphometric analysis, zoological activity