Influence of Temperature on Nitrification in Soils

Abstract Nitrification of ammonium sulfate as influenced by temperature was studied in 3 Iowa soils in the laboratory and in 1 soil under field conditions over a fall and winter season. Laboratory temperatures ranged from 8° to 30° C. and soil temperature in the field varied from freezing to about 20° C. General relationships were established between temperatures and nitrification rates in given soils. Nitrification rate decreased with diminution in soil temperature; however, the relationship was not linear over the entire temperature range. At given temperatures, ammonia oxidation rates differed between soils studied, but the temperature‐nitrification rate curves for the 3 soils were similar and differed only by a constant factor. Of particular importance to this study was the influence exerted on nitrification by temperature as it decreased from optimum to critically low temperatures. Complete inhibition was not attained until soil temperatures approached the freezing point. Only slight oxidation of ammonium occurred, however, under field conditions in soils that were fertilized after soil temperatures had decreased below 50° F.