Abstract Little information is available on the short-term effects or cropping on soil organic-matter content or composition. The carbohydrate composition of a clay soil and of its particle size fractions after 2 yr of cropping to barley and alfalfa was determined and compared to a fallow (bare soil) control. Larger amounts of carbohydrates were found in the whole soil under barley and alfalfa than under fallow. While only small effects of cropping were detected in the silt or clay fractions, cropping to barley and alfalfa resulted in larger C (24–60%), N (36–45%) and carbohydrate (46–83%) contents in the sand fraction compared to the fallow control. This suggests that differences observed in the whole soil can be specifically attributed to differences found in the sand fraction. Differences in composition and origin of the carbohydrates in the whole soil and in its size fractions were small between cropping treatments.