Comparison of porosity in a Chernozemic clay loam soil under long-term conventional tillage and no-till

Abstract

Tillage practice can alter soil structure, porosity and the size distribution of pores. Consequently, this study was conducted to compare the long-term (since 1968) effects of conventional tillage (CT) using a heavy-duty cultivator and no-till (NT) on structure and porosity of a Dark Brown Chernozem (clay loam) soil in southern Alberta. Number and porosity of total, round, intermediate and elongated pores, maximum equivalent circular diameter (MECD), and mean circularity of pore sizes 50–500 µm (P-150), 500–1000 µm (P-500) and >1000 µm (P-1000) diameter were quantified. These parameters were determined for three depths (0–10, 10–20 and 20–30 cm) and two orientations (vertical, horizontal) using UV-dye impregnated soil sections and image analysis. The surface soil (0–10 cm) of CT was dominantly granular-spongy, but for NT it was dominantly crack to massive. Since tillage treatments were not replicated, only general trends on the effect of tillage and its interaction with depth and orientation are given and probability levels are not reported. Tillage treatment had an influence on P-150 and P-500 pores but little or no influence on P-1000 pores. Mean number and porosity of total and intermediate P-500 pores, which are the most important pore size class for seedling root growth in these soils, were higher for CT than NT for the surface soil, but were higher for NT than CT for the subsoil. For example, the total porosity of P-500 pores was 2.21% for CT and 1.95% for NT at the 0- to10-cm depth, 3.80% for NT and 2.27% for CT at the 10- to 20-cm depth, and 3.18% for NT and 2.80% for CT at the 20- to 30-cm depth. These results suggested a higher potential for seedling root growth in the surface soil of CT, but a greater potential for root growth in the subsoil of NT. Key words: structure, porosity, image analysis, tillage