Soil water content and freezing temperature affect freeze–thaw related N2O production in organic soil

Abstract

An organic agricultural soil was exposed to freeze–thaw cycles (FTC) using either intact soil cores or cores packed with homogenized soil. The cores were first exposed to two mild FTCs (–1.5 °C/+4 °C) with soil water content being 56–85% of the water-filled pore space (WFPS). Both intact and packed soil cores showed high N2O emissions when the soil was thawing and had high WFPS. The second freeze–thaw cycle induced lower N2O emission than the first. After the mild FTCs, a deep frost (–15 °C) was applied. This greatly increased the N2O emissions when the soil was thawing. Freezing–thawing had a smaller effect on CO2 than on N2O release. The results show that both soil moisture and the severity of frost modify the N2O burst after thawing, and N2O release (denitrification) was favoured more by FTC than heterotrophic microbial activity (CO2 production) in general. The possible reason for this difference is discussed.