The Nitrogen and Phosphorous Cycle in Soils - FSA-2148

Nitrogen exists in soils in many forms and constantly changes from one form to another. The paths that the different forms of nitrogen follow through the ecosystem are collectively called the nitrogen cycle (Figure 1). Understanding how the different pools of nitrogen interact and the processes by which these forms enter and leave the cycle is the subject of continuing study. Nitrogen is found in both inorganic and organic forms. Soil organic matter is composed primarily of amides (NH2) and accounts for more than 90 percent of the total nitrogen present in most environ­ ments. In general, nitrogen is not found associated with soil minerals, as is the case with phosphorus. Some clay minerals may tie up small amounts of nitrogen in the ammonium form (clay fixation) but not in the same magnitude as phosphorus. Organic Nitrogen