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Cultivation Effects on Carbohydrate Contents of Soil and Soil Fractions

Queensland Wheat Res. Inst., P.O. Box 5282, Toowoomba 4350, Australia

*Corresponding author.

ABSTRACT

The distribution of monosaccharides in the acid hydrolysate of soil fractions and whole soils subjected to variable periods of cultivation (0–45 yr) were studied because carbohydrates constitute a substantial proporation of soil organic matter and affect soil aggregation, both of which are affected by cultivation. Monosaccharides in soil acid hydrolysates were analyzed as their alditol acetates by an improved procedure using 1-methylimidazole as acetylation catalyst. Carbohydrate constituted from 8 to 16% of soil organic matter in virgin soils and generally increased with the clay content (18–78% clay). Of this, 27 to 43% of carbohydrate was present in the light fraction (<2 Mg m^–3), which also contained proportionally more carbohydrate-C than did total organic matter. Upon cultivation, the light fraction declined rapidly, resulting in substantial loss of carbohydrate, especially in clayey soils. In these soils, carbohydrate losses also occurred from sand-size and silt-size fractions but clay-size carbohydrates were less affected. Glucose and galactose were normally the predominant monosaccharides in the acid hydrolysates of the soils and soil fractions. The effects of cultivation on the net amounts of carbohydrate-C in the various fractions and the whole soil in the three soil series studied, were generally similar to those on the total organic C, showing thereby that carbohydrate fraction of the soil organic matter was no more liable than the total organic C.

Contribution from Queensland Wheat Res. Inst. Toowoomba, Australia.

Received for publication November 24, 1987.