MINERALIZATION AND IMMOBILIZATION OF SOIL AND FERTILIZER NITROGEN WITH NITRIFICATION INHIBITORS AND SOLVENTS

Rates of transformations of fertilizer N and soil N were measured in three soils labelled with ((NH4)2SO4)-N-15 in laboratory experiments of short duration (7 days). The effects of three nitrification inhibitors (N-Serve 24E, 2-ethynyl pyridine, ATC) applied to three soils in aqueous solution or emulsion, or of three solvents (water, ethanol, acetone) applied to one soil with or without an aqueous solution of N-Serve TG, on rates of nitrification, N immobilization and N mineralization were measured. Nitrification inhibitors had little or no effect on N transformation rates apart from nitrification. N immobilization rates (fertilizer or gross) and N mineralization rates (net or gross) were either not affected or only slightly affected by addition of the three inhibitors at 15-mu-g g-1 soil. Organic solvents inhibited nitrification and more N was immobilized and less N was mineralized in the presence of organic solvents, resulting in reduced net N mineralization or net N immobilization. The effects of organic solvents on N transformation rates were temporary and were due to the addition of an energy source rather than to inhibition of nitrification. The work reported here indicates that nitrification inhibitors, or organic solvents used to dissolve inhibitors which are sparingly soluble in water, have only transient effects on biological transformations of N in soils in the absence of growing plants.