Physics · Biogeochemical Cycles

With reference to the nitrogen cycle, consider the following statements: I. Nitrogen constitutes a major proportion of Earth's atmosphere, but most living organisms cannot directly utilize atmospheric nitrogen. II. The largest reservoir of nitrogen in the biosphere is found in soil organic matter rather than in the atmosphere. III. Human activities such as the excessive use of nitrogen-based fertilizers have significantly altered the natural nitrogen cycle. How many of the statements given above are correct?