PHYTOTOXICITY OF FRESH AND COMPOSTED WOOD WASTES APPLIED AS ORGANIC AMENDMENTS IN SOIL

A germination test with cress (Lepidium sativum L.) was carried out to evaluate the phytotoxic effects of extracts from fresh and composted tree clippings. Water-soluble extracts from unground and ground material were compared with a soil solution and distilled water in relation to their effect on germination and plant root development. Water-soluble and ethanol-soluble extracts from fresh tree clippings were strongly acidic, but they were neutral for the composted material. Greater quantities were extracted by water and alcohol from fresh material than from composted material. Water-soluble products extracted from fresh ligneous materials decreased the rate of germination of cress very significantly compared with those obtained from composted tree clippings. Grinding the clippings further reduced the germination rate, through the apparent liberation of more phytotoxic products. Composting of tree clippings significantly decreased the phytotoxicity of the organic amendment.