Organic matter is an essential component of soil. It increases the ability of the soil to provide the proper conditions to grow agricultural crops and to resist processes such as soil erosion. Soil organic matter is composed of many different components, the most important being various forms of carbon and nitrogen. The decomposition of the organic carbon and nitrogen in soil releases nutrients to growing crops. Knowledge of how this decomposition occurs will help farmers predict how much fertilizer is needed and not over apply fertilizer which may cause environmental problems. Thus, understanding the nature of soil carbon and nitrogen is very important and an area of active research. Part of that research is directed at obtaining estimates of how much soil organic carbon is presently in many of our soils and to set up permanent sampling locations so that the amounts of soil carbon can be monitored with time. This gives us an indication of the 'State' of the soil resource and whether our current farming management is ensuring that the resource is sustainable. This study used different methods to characterize the different forms of soil organic C and N, at a large number of southern Ontario sites where significant amounts of other information had already been collected. The similarities of the different methods and the influence of other soil properties such as the amount of sand content were determined. A chemical extraction method for predicting the amount of nitrogen which might be released by the biological breakdown of soil organic matter was developed. It gave very similar estimates to a long term (22 weeks) incubation method which measures the release of nitrogen during biological decomposition. The quick extractant method may be a good soil test for farmers to use in making decisions on the amount of fertilizer nitrogen to apply. In addition, the study characterized in detail the seasonal changes in soil organic C and the amount of variability within the monitoring area at any time, for 3 different fields. This allows the accuracy of the estimate of soil organic C to be determined and thus, the accuracy of any future estimates of how much change has occurred. At these sites, the amount of soil that has been lost or gained from soil erosion was the main factor in determining the amount of soil carbon present and also the amount of crop yield that was obtained. An easily measured soil erosion tracer, 137-cesium, was used to determine the amount of soil loss or gain at a site and was recommended as a useful indicator for determining the 'State' of the soil resource. Finally, all measurement were included in an electronic database with geographic locations so that the information can be used for future studies examining how the soil resource is changing.