CARBON, NITROGEN, SULPHUR, AND PHOSPHORUS IN SOME SCOTTISH SOILS

Summary An examination has been made of carbon, nitrogen, sulphur, and phosphorus relationships in ten surface soils from each of five parent‐material groups (calcareous, granite, slate, Old Red Sandstone, basic igneous) in North Scotland. Except that the calcareous soils contain about 40 per cent. less organic carbon, there are no significant differences in the mean contents of total nitrogen and organic carbon. These are highly correlated, but the C: N ratio varies inversely with the base status of the parent material, ranging from 11·3 in the calcareous group to 17·0 for the granite soils. The total sulphur content is very similar for the four non‐calcareous groups, but much higher in the calcareous soils, due to the presence of varying amounts of water‐insoluble sulphate, closely related to the calcium carbonate content. Small proportions of this sulphate may be combined with barium and strontium, but most of it is probably present as a co‐crystallized impurity in the calcium carbonate. There is a close overall relationship between total sulphur, nitrogen, and organic carbon in the non‐calcareous soils and a similar relationship for nonsulphate sulphur in the calcareous group, giving a mean C:N:S ratio of 140 : 10: 1·4 for the five groups. This is similar to ratios from other countries, indicating the general importance of sulphur in soil organic matter. The organic phosphorus is highest in the basic igneous group and lowest in the calcareous soils, where it comprises 40 per cent. of the total phosphorus compared with 52‐61 per cent. in the non‐calcareous groups. The proportion of organic phosphorus to the other elements is about 50 per cent. less in the calcareous group, the mean C: N: S: P ratio being 113:10:1·3 :1·3, compared with 147: 10:1·4: 2·5 for the non‐calcareous soils. Probably due partly to varying accumulation of inositol phosphates and other resistant forms, the correlations of organic phosphorus with carbon and nitrogen are much lower than for sulphur, and it appears to be a less integral part of the organic matter.