CHARACTERIZATION OF THE PORE-SPACE OF A C LAY SOIL - INFLUENCE OF SOIL CONSTITUENTS AND TILLAGE PRACTICES

The objective of this study was to compare the effects of three tillag e treatments and soil constituents on soil porosity characteristics. T he experiment was initiated in the fall of 1987 on a Kamouraska clay ( Orthic Humic Gleysol). Moldboard plowing, chisel plowing and no-till w ere compared during the fourth growing season of a continuous barley ( Hordeum vulgare L.) system. Surface soil samples were taken in late Ma y 1991 after seeding and at the beginning of October before primary ti llage. Soil porosity was characterized by measuring the total porosity and its textural, structural and shrinkage components. The tillage tr eatments had no significant effect on total porosity. In May, however, the structural porosity was 25% larger under moldboard plowing than u nder no-till. On average for the two sampling dates, the interclod por osity was 51% larger under moldboard plowing than under no-till. In ad dition, this component of the structural porosity increased during the growing season under all treatments. In May, the shrinkage porosity d ecreased progressively from moldboard plowing to chisel and to no-till whereas the reverse trend was observed in the fall. Textural porosity was positively correlated with clay and organic carbon contents. This study shows that tillage affects mainly the structural porosity and i n particular its interclod and shrinkage components.