PHYTOTOXICITY AND FERTILIZER VALUE OF DIF FERENT ORGANIC MATERIALS

Six different organic materials, two of them with a vary evolved organ ic matter (peat and leonardite) and the other four being recently form ed (a sewage sludge, SS, a municipal solid waste, MSW, a compost from a mixture of SS and MSW and sheep manure) were characterized from a ch emical and biochemical point of view. The fitotoxicity and agronomic v alue of those materials were evaluated by both, an experiment of seed germination on aqueous extracts from the organic materials and by grow ing ryegrass on a soil treated with these materials at two different r ates. SS, sheep manure and MSW (raw materials) inhibited seed germinat ion suggesting the presence in the organic extracts of phytotoxic subs tances. A negative correlation was found between the germination index and the values of EC and the water soluble C/N ratio of the materials . In the first harvest, the high rate of the raw materials depressed y ield while the materials with a more stabilizer organic matter (peat, leonardite and compost) increased control yield. In the second harvest all the material showed, at any rate, yields higher than that of the control. The phytotoxicity observed with the raw materials disappeared or decreased some time after their addition to soil showing these mat erials a noticeable positive residual effect on the crop.