Effects of cultivation and erosion on soils of four toposequences in the Canadian prairies

This study evaluates the effects of cultivation and topography on soil properties. Four toposequences (one uncultivated and three cultivated since 1910, 1930 and 1961) were sampled and their horizon depths, bulk densities, soil losses, organic carbon (C), total nitrogen (N), and total phosphorus (P) contents compared. Thin sola and A horizons with relatively high bulk densities and low amounts of organic matter, total N and total P at upper slope positions on cultivated fields indicated maximum erosional activity. Organic matter, total N and total P contents were increased in areas of deposition at lower landscape positions, whereas the thickness of the sola and A horizons increased and bulk density decreased. Substantial reductions in N, in excess of the amount removed by grain and straw, occurred with continuing cultivation. Lower slopes lost less N on a percent basis but absolute losses were greater than on upper slopes. Long term P fertilization maintained total P in the A Horizon of cultivated toposequences at levels similar to the thicker A horizon of the Native toposequence. Losses of P from non-eroded sites were comparatively less than losses of C or N. If the cultivated toposequence as a whole is considered, the largest C losses were due to mineralization in lower slope areas and were more than double the amounts lost by erosion at upper slope areas. In upper slope areas mineralization accounted for the largest portion of total C lost in the early years of cultivation, whereas erosion accounted for the largest portion in later years.