STORAGE OF CARBON, NITROGEN AND PHOSPHORUS IN CULTIVATED AND ADJACENTFORESTED SOILS OF ONTARIO

The amounts of C, N, and P stored in soils represent the balance betwe en inputs and outputs of these elements to and from terrestrial ecosys tems, Soil management and unintentional perturbation of element cycles (e.g., inputs of pollutants) may profoundly influence soil organic ma tter and associated nutrients, Reliable information on changes in C, N , and P stored in soils is essential to prevent ecosystem degradation, Agricultural land in Ontario is managed intensively, but quantitative information about the influence of management on element storage is l acking, Our main objectives were to quantify the masses of soil C, N, and P stored in soils from the agricultural regions of Ontario and to assess the impacts of agriculture by comparing soils under cropland an d adjacent forests or woodlots. These assessments are valid to the ext ent that adjacent forests are appropriate 'ecological references', suc h that differences between soils under cropland and forest represent t he cumulative effects of clearing and subsequent agricultural manageme nt, Mass of C, N, and P per unit area stored in surface and subsurface layers of cropland and adjacent forests was measured for 15 sites, Th e influence of two or more cropping practices was assessed at six of t he sites. Compared with the forest soil, the surface layers of the cul tivated soils (averaged for the 15 sites) had 34% less C, 19% less N, and 24% more P,Decreases in C storage were attributed to reduced C inp uts and enhanced rates of plant litter decay. Changes in N storage wer e dependent on management of N fertility, and cultivation-induced narr owing of C/N ratios indicated preferential maintenance of N relative t o C storage, Increases in P storage were attributed to fertilization,T hese quantitative comparisons indicated that decreases in C storage we re less severe than frequently suspected and that the increases in P s torage may have an equally important influence on ecosystem function.