The effect of storing soils at −20° on their subsequent ability to mineralise nitrogen on incubation differs according to the soil, because significantly more mineral‐N (ammonium‐and nitrate‐N) and nitrate‐N was produced by three of four soils tested. These increases, apparently induced by freezing and thawing, may have been partly related to the moisture and carbon contents of the soils. Samples stored for different periods up to 6–9 months differed little in their rates of mineralisation. Experiments with added ammonium‐N suggested, however, that numbers of nitrifying organisms decreased after 6 months storage.

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