Many soils of the arid west have a rich active azofying flora. This is due in no small measure to their composition. They are high in calcium and magnesium carbonate and contain a good supply of available phosphorus and potassium but have a low nitrogen content. They are poor in organic carbon; hence, their native supply of energy is limited. It is well-known that a liberal supply of rapidly decaying organic matter is beneficial, and this is being supplied to some soils in the form of manures. This will increase the nitrogen content of the soil. What effect will this increase have upon the nitrogen-fixing powers of the soil? It is the province of this bulletin to consider some of the results which have been obtained in seeking an answer to this question.
Greaves, J. E. and Nelson, D. H., "Bulletin No. 185 - The Influence of Nitrogen in Soil on Azofication" (1923). UAES Bulletins. Paper 151.