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Equations for Following Nutrient Transformations in Soil, Utilizing Tracer Data: II.¹

ABSTRACT

Theoretical equations are derived for calculating mobilization and immobilization rates, from observable data, in a tagged atom system of available and unavailable (mobile and immobile) plant nutrients undergoing simultaneous interchange in soil. The equations are needed since the rates, at least by present methods, cannot be measured directly. The theory is more general than that developed by the authors previously, no restrictions now being placed on the relative amounts of the available and unavailable material. Two cases are considered: (1) the mobilization rate m and the immobilization rate i are constant; (2) m is proportional to the amount of unavailable material and i is proportional to the amount of available material, the assumption in case 2 being that of mass action. Certain experimental data are analyzed and it is found, for these data, that the theory for case 2 is in good agreement with the experiments. It is pointed out that the theory for case 1 should be applicable in some other instances, especially if the time intervals in question are small.

¹ Journal Paper No. J-2605 of the Iowa Agr. Exp. Sta., Ames, Iowa, Projects 998 and 1070. Contribution of Agronomy Department. Presented before Division III of the Soil Science Society of America, Saint Paul, Minn., Nov. 10, 1954.

² Professor of Soils and Physics, and Associate Professor of Soils, respectively.

Received for publication October 22, 1954.