Most soils contain sufficient nutrients for normal plant growth, with the exception of nitrogen, phosphorus and potassium. These elements are used by plants in the largest quantities and the amounts of these in the soil govern its productivity. Soil organic matter is of prime importance for it is the matrix which holds the nitrogen and modifies the structure, temperature, and water-holding capacity of the soil. The organic matter is the very life of the soil, for it is in and on it that bacteria work and by so doing determine the kind and speed of reactions which occur. It is the bacterial activities in the soil that determine the available plant food. Probably most Utah soils contain sufficient potassium, consequently the problem of Utah soil fertility resolves itself into maintaining an optimum concentration of nitrogen, phosphorus, and organic matter. The present work represents a study of the phosphorus, nitrogen, and organic matter in the soil and the speed with which they are being removed by plants, erosion and leaching.
Greaves, J. E. and Hirst, C. T., "Bulletin No. 310 - The Influence of Cropping on the Nitrogen, Phosphorus and Organic Matter of the Soil Under Irrigation Farming" (1943). UAES Bulletins. Paper 272.