Phytotoxicity of organic amendments on activities of select soil enzymes
Madejón, Engracia | Burgos, Pilar | Murillo Carpio, José Manuel | Cabrera, Francisco
Three organic materials, a municipal solid waste compost (MWC), a paper sludge (PS) and an agroforest compost (AC), were tested to relate their stability to the corresponding soil enzyme activity resulting from their application. PS and AC were stable materials, free of phytotoxic substances, although AC presented direct toxicity due to its high salinity and inhibited seed germination. The presence of heavy metal does not seem playing an important role in the phytotoxicity of the tested materials since, the highest values of germination index were obtained with PS material despite its high heavy metals concentration. However, MWC presented a low level of maturity affecting negatively seed germination, and indicating an inaccurate composting process. The application of the three organic materials to a sandy soil (at a rate equivalent to about 50,000 kg ha-1) increased soil enzyme activities (dehydrogenase, β-glucosidase, urease and benzoylargininamide hydrolyzing (BAA)) with respect to the control (soil without organic matter application) during one month of incubation. The positive effect of the organic materials on enzyme activities was more pronounced in the case of the MWC, a fresh organic residue having low organic matter stability. It suggested that the presence of phytotoxic substances did not affect negatively soil enzyme activities. Probably, molecules or promoters released by decomposing organic compounds which affect negatively seed germination, enhance enzyme activities.
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