1. Experiments have been made to determine the effect of treating alkaline soils with manganese sulphate on the quantities of manganese which can be extracted by N-ammonium acetate.
2. Two soils of known total and ‘extractable’ manganese content were treated with manganese sulphate solution in the laboratory and re-analysed after definite time intervals. In the first of these, a calcareous soil from the College Farm, the extractable manganese decreased for 14 days after treatment, after which time manganese was again liberated, presumably due to a waterlogging effect. The extractable manganese in the second soil, a slightly alkaline soil with a high organic matter content, increased appreciably after treatment and remained at this level for the duration of the experiment.
3. An experiment conducted in the field on a highly calcareous soil showed that the extractable manganese content down to a depth of 12 in., had fallen to its original level only 7 days after treatment. This behaviour is in agreement with the observations of other workers that there is little residual effect from manganese sulphate treatment for subsequent crops. The desirability of performing similar experiments on other soils is suggested.
4. The effect of waterlogging and steam sterilization was to increase the quantities of extractable manganese in the soils examined.
The authors wish to express their grateful thanks to Mr B. S. Furneaux, M.Sc, for the descriptions of the soils investigated, and to Dr N. H. Pizer for his valuable suggestions in the preparation of this paper. They are also indebted to Mr J. Hargrave of the Agricultural Institute, Kirton, Lines, for providing the Bourne Fen soil, and to Mr J. Tinsley, B.Sc., for pH and organic matter determinations.