Increasing stress is being placed on the environment by man's activities including those of changing land usage for increased food production and the release of carbon dioxide due to fossil fuel combustion. Further stresses may occur if agricultural practice is modified by using plant products for liquid fuels. Rational management of these activities can only occur if there is a thorough under standing of the biogeochemical cycles of the major plant nutrients, carbon, nitrogen, sulfur and phosphorus. A vital part of this understanding concerns the interactions between these cycles, where in...