Changes in soil morphology on a chronosequence of no-till agricultural soils
Soil scientists, particularly pedologists, have begun to realize that important information on soil processes lies 'within' genetic soil horizons. Short-term changes in soil morphology are evaluated in this thesis through utilizing relatively new techniques. Sampling bulk soil in fine increments (i.e. 1 cm thick layers) with soil depth, 137Cs as a marker of short-term changes, and the image analysis of the soil micromorphology on thin sections were techniques employed to assess the recent soil genesis along a chronosequence of no-till soils in southern Ontario. It was determined that earthworms, the lack of organic matter incorporation, and physical disruption by annual tillage were important factors influencing the morphology of the soils after 11 years of no-till conservation management. Earthworm populations were much greater in the no-till soils and this had a major influence on aggregation, incorporation of surface-applied organic matter and soil porosity. Soil organic matter increased in the top 5 cm of the soil profile as the number of years in no-till increased. The no-till soils had greater horizontally-oriented elongated macropores in the top 5 to 15 cm of the soil profile relative to soils in conventional tillage due to the lack of tillage and exposure to annual freeze-thaw processes. Rounded macropores increased with the number of years in no-till as these pores are maintained each year due to the lack of tillage and greater faunal activity in the no-till soils. Micromorphological evidence indicated surface crust formation in some of the conventionally-tilled soils. Other micromorphological evidence showed that the top 3 cm of soils in no-till for 11 years were similar to those in a never-cultivated woodlot soil. This research concluded that major morphological changes occur in top 30 cm of soils as they are converted to no-till from conventional tillage practice.