Measurement of the polysaccharide content of soils

Abstract

The polysaccharide content of two soils, measured by precipitating and weighing the microbial gums from the fulvic acid fraction of soil organic matter, and by colorimetric analyses using anthrone, was increased appreciably during the incubation of samples with straw. Applications of nitrogen and phosphorus altered only slightly the amount of polysaccharides present. The polysaccharide content of the amended soils increased rapidly during the first week of incubation and then levelled off. Peptization of the soil with dilute alkali prior to acid hydrolysis substantially increased the carbohydrates measured with anthrone. The anthrone reagent which measures primarily hexoses indicated a soil carbohydrate content of 10–15 per cent occurring in a range of Saskatchewan soils. Thirty-five per cent more carbohydrate carbon was found using the less specific phenol-sulphuric acid reagent. The acetone precipitated fraction from the fulvic acids accounted for only 10 per cent of the soil carbohydrates and contained a large proportion of ash and other non-carbohydrate materials. The total acid-soluble base-soluble fraction, fulvic acids, contained 15–25 per cent; the remainder was distributed in the alkali insoluble humin — 55–70 per cent and the humic acid fraction 4–12 per cent.