Brief and vigorous N ₂ O production by soil at spring thaw

SUMMARY In an acid sandy loam soil (pH 3.8), field production of N 2 O was two orders of magnitude higher at thaw in the spring than at any time during the rest of the year. Soil thaw in midwinter did not result in any increase in N 2 O flux. Soil water content remained at, or above field capacity during measurements; nitrate was added in excess. This effect could be reproduced in the laboratory: thawing soil cores at controlled temperature, nitrate and moisture yielded a large flush of N 2 O compared to an unfrozen control. The results indicate the importance of microbial N 2 O production during thaw for total annual N 2 O‐emission.