THE EFFECT OF CHARCOAL ON THE GROWTH OF LEGUMINOUS PLANTS IN SAND CULTURE

Abstract

The addition of small proportions (0.5‐2.0 %) of activated charcoal to the rooting medium of inoculated peas in nitrogen‐free sand culture resulted in marked increases in dry weight of the plants and in nitrogen fixation. Wood charcoal in larger proportions had a similar effect, while animal charcoal severely inhibited growth. The number of nodules was greatly reduced in the presence of activated charcoal, but such nodules as formed were much larger and the nodule tissues per unit weight were more active in nitrogen fixation. Activated charcoal also led to an increase in dry weight of non‐inoculated peas supplied with inorganic combined nitrogen. It is tentatively suggested that these favourable effects arise from the adsorption by the charcoal of harmful excretions from roots or micro‐organisms or of excess nutrients, and from the maintenance of a more favourable pH in the rooting medium. The examination of barley intersown with the peas, and the results of Kjeldahl analyses on the rooting media, provided no evidence that the enhanced fixation in the presence of activated charcoal was attended by any considerable excretion of fixed nitrogen.