EFFECTS OF FREEZING AND THAWING ON SOME CHEMICAL PROPERTIES OF THREE SOILS

The effect of continuous freezing at −15 C and alternate freezing and thawing on some chemical properties of three Saskatchewan soils was determined. The results are based on soils treated while moist with methyl bromide and freeze-dried following the frost treatments. The freezing effects were obtained by comparisons with air-dried control samples. Alternate freezing and thawing resulted in a large increase in exchangeable NH 4 -N and a small but significant decrease in exchangeable K; there was no effect on cation exchange capacity or exchangeable Ca ++ and Mg ++ . Freezing and thawing did not affect NO 3 -N content. Dilute NaHCO 3 -extractable N and water-soluble carbohydrates, as indices of available N, increased sharply after continuous freezing, but alternate freezing and thawing gave a further increase in NaHCO 3 -extractable N only in one soil. There was an increase in NaHCO 3 -extractable P after continuous freezing and a further significant increase following alternate freezing and thawing. The large increase in exchangeable NH 4 -N as a result of alternate freezing and thawing was not reflected in an increase in N uptake by barley seedlings grown on the frost treated soils. Generally there was good agreement between N uptake and available N results. The uptake of P by the barley seedlings did not reflect the increase in NaHCO 3 -extractable P as a result of the frost treatments.