Effect of Added Salts on Nitrogen Release and Nitrate Levels in Forest Soils of the Washington Coastal Area

The release and mineralization of N was studied in incubated samples of 10 forested soils from the Washington Coast which had been treated with a variety of salts. Salts were added in solution at 0.005, 0.05, and 0.2 M concentrations and the samples were incubated at 27C for 7, 14, and 21 days. Release of NH 4 ‐N plus NO 3 ‐N increased with increase in the duration of incubation and concentration. The lowest concentration of salt increased N release over that from distilled water. The order of the effect of salts on release of N was AlCl 3 > CaCl 2 > KCl > K 2 SO 4 > K 2 CO 3 > K 2 HPO 4 . At the lowest concentration, salts had little effect on nitrate levels, but at higher concentrations, nitrification was reduced in all soils by chloride salts. Nitrification was also reduced by K 2 SO 4 but the reduction was evident only at the highest concentration. In contrast, nitrification was increased in the majority of these soils by K 2 CO 3 at the two higher concentrations and by K 2 HPO 4 at the highest concentration. Of the four soils in which nitrification was not increased, three had the highest nitrification capability of all soils studied, as evidenced by the high levels of nitrate produced when incubated with water. Implications of the study concern the influence of fertilizers, lime, and ash from burning on availability of native soil N and formation of nitrate, and the effect in these soils of different N fertilizers on mineralization of soil N and nitrate levels.