After the removal of light fraction from soils under old pasture and under continuous fallow-wheat rotation, carbohydrates were extracted using IN HC1 followed by 0.5N NaOH and finally an acidic acetylation procedure, or by a single extraction with 0.2N NaOH only. The sequential extraction procedure removed 70-80 % of the carbohydrate from the soil under both agronomic systems. 0.2N NaOH removed a larger proportion of the carbohydrates from soil under fallow-wheat rotation (43-52%) than from soil under old pasture (35-38%). The composition of the carbohydrates in a given extract from the soil under pasture or fallow-wheat was similar. This similarity extended even to the neutral sugar composition of fractions obtained by gel filtration of the purified extracts. Generally, low molecular weight materials were rich in amino acids and compounds such as glucose, ribose, and glycerol. Polymers of molecular weight 4000-100,000 contained relatively high proportions of uronic acids and amino acids. Least amino acids were present in materials of molecular weight greater than 100,000 which contained appreciable quantities of deoxyhexoses (up to 20% of the total neutral sugars) indicative of their microbial origin. Against this background of similarity, certain differences between the carbohydrates from soils under pasture and fallow-wheat rotation were apparent. 1N HCl extracts contained more high molecular weight material from the old pasture soils than from the cultivated soil. The composition of these extracts indicated that they comprised the easily extractable recently synthesized microbial polysaccharides. The proportion of such polymers was lower in the cropped soil. A higher proportion of materials of small size was present in soils under a wheat crop. Maximum amounts of these compounds were present during periods of maximum plant and microbial activity. Extracts from soils under fallow-wheat rotation contained a higher proportion of uronic and amino acids and less ribose, arabinose, and deoxysugars than the extracts from soils under pasture. Based on relative deoxysugar contents it was calculated that the pasture soil contains about four times as much microbial polysaccharide as the soil under fallow-wheat.
Methods for extracting polysaccharides from soil have been evaluated with respect to yield and polymer degradation. Maximum extraction with a single non-degradative treatment was obtained by shaking soil with 0.5N NaOH for 16 hr at 20�C. Pretreatment of the soil with cold dilute hydrochloric and hydrofluoric acids raised the extraction efficiency to over 40% of the total soil carbohydrate. The carbohydrates removed by 0.5N NaOH at 20�C and by hot water and other lower-yielding reagents were of comparable molecular size. Hot 0.5N NaOH treatment and acidic acetylation both removed more carbohydrate than cold 0.5N NaOH but caused considerable degradation. About 80% of the carbohydrate was removed from a range of soils by extracting first with 1N HCl, followed by 0.5N NaOH, and finally acetic anhydride containing 2.5 % conc. H2SO4. Humic materials were removed from the 0.5N NaOH by passing the extract upwards through a column of Dowex 50 (H+). Other coloured materials were adsorbed from the effluent by a water-insoluble cross-linked polyvinyl-pyrrolidone, and final purification and desalting were achieved by gel filtration. The 'purified' polysaccharide contained neutral sugars 55%, hexosamines 6%, uronic acids 10% (minimal value), amino acids 6 %, nitrogen 2.1%, and ash 1.8%. At least 10 neutral sugars, 2 hexosamines, 2 uronic acids, and 16 amino acids were present. The polysaccharides had a wide molecular weight distribution.
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