Denitrification and ammonification at low soil temperatures

Abstract

A laboratory study was conducted to determine the effects of temperatures from −2 to 25 °C on denitrification and ammonification in anaerobic soil treated with alfalfa or glucose. Organic C substrate as alfalfa or glucose increased denitrification rates at all temperatures within this range and lowered the threshold temperature at which denitrification occurred. The threshold temperature for denitrification was as low as −2 °C in unfrozen (supercooled) soil in contrast to most other studies where the threshold temperature was reported to be at or above 0 °C. When soil was frozen at −2 °C, the denitrification rate was much lower than in unfrozen soil at the same temperature. A square root model was employed which showed that the square root of the denitrification rate was linearly related to temperature from −2 to 25 °C. The maximum amount of [Formula: see text] produced during the incubation periods generally decreased from −2 to 25 °C and was greatest when glucose and especially alfalfa were added. The rate of ammonification increased with addition of alfalfa but the quantities of [Formula: see text] produced generally decreased from 25 to −2 °C. Key words: Threshold temperature, frozen vs. unfrozen soil, nitrite production, square root model