Glucose, alfalfa insolubles, and complete alfalfa uniformly labeled with carbon‐14 were added to an organic soil to determine under controlled conditions, if the loss of the soil due to biological decomposition could be counteracted. Carbon‐14 labeled material was used so that it could be determined whether or not there was an increase in the decomposition of the native organic matter as a result of the added material, and, if this was true, whether the soluble fraction of the added materials, or the insoluble fraction, was chiefly responsible. The materials were added, the soil incubated, and CO2 collected at intervals. The insoluble fraction of alfalfa caused a larger breakdown of native organic matter than solubles alone or complete alfalfa. It was impossible to build up the organic content of the soil, under these conditions, but the net loss of carbon was diminished by the addition of the organic materials.

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