CHEMICAL-WEATHERING IN SOILS FROM THE GLACIAL LAKE-AGASSIZ REGION OF MANITOBA, CANADA

Recently, there has been considerable interest in categorizing the ava ilability of plant essential nutrients and selected transition metals in the soil environment so as to predict their effects on ecosystem he alth and the efficacy of potential management practices. Researchers d esire to isolate important soil properties, determinant biotic activit ies and fundamental pedogenic processes that control biogeochemical cy cling and are potentially modifiable for the goal of ecosystem sustain ability. In a relative sense, a significant portion of this scientific effort has been directed towards temperate and tropical forest ecosys tems, with relatively less attention given towards understanding the b oreal forest ecosystem. Consequently, an investigation was undertaken near Thompson, Manitoba, to: (1) determine the extent of weathering of the principal soils, (2) employ a selective-sequential chemical extra ction method to categorize the soil-chemical fractions responsible for nutrient availability, and (3) infer the importance of selected soil forming processes responsible for soil genesis and nutrient availabili ty. Preliminary findings suggest that nutrient availability is related to the nutrient concentration in the cation exchange fraction and/or to nutrients sequestered by the organic fraction. The metals in the ma nganese, noncrystalline and crystalline iron oxide fractions may be bo und so tightly to these oxides that they are largely unavailable to pl ants; however, they are largely responsible for buffering the more lab ile pools against gradually changing vegetational and climatic conditi ons.