EVALUATION OF PORES UNDER DIFFERENT MANAGEMENT-SYSTEMS BY IMAGE-ANALYSIS OF CLAY SOILS IN SASKATCHEWAN, CANADA

The influence of tillage operations on soil porosity is not yet completely understood and requires further attention. Image analysis was used to evaluate the impact of deep ripping and paraplowing on soil porosity in two lacustrine soils in Saskatchewan. Large undisturbed soil samples (25 x 20 x 15 cm) were collected after harvest, and dried by the acetone immersion technique to avoid shrinkage. Four thin sections of 11 x 8 cm were prepared from each sample and video images were acquired from the thin sections, using a Contron IBAS image analysis system. Total porosity > 50-mu-m of the soils from the control parcels was high and appeared to be adequate for normal crop growth. Increased amounts of clay likely increase the percent of soil porosity by a natural swell-shrink process. Deep ripping increased the porosity of soils in the surface horizon, whereas the influence of paraplowing was evident at 30 to 60 cm depth. The increase occurred as pores with a shape factor (SF) < 0.2 and a width > 2 mm. Thus, the two tillage methods used in this study caused an increase in large planar voids. In general, tillage has little influence on non-planar voids (SF > 0.2) as they occur in the aggregates and they are not destroyed by cultivation. Despite the increase in porosity at the Lucky Lake site by deep tillage, no increase could be found in crop production in this region, suggesting that this tillage operation is not needed in the dry Chernozemic soil. Considering their dynamics, pores should be measured more frequently and over a long time, so that a clearer picture could be obtained for better management of soils.