Phytotoxicity of olive tree leaf compost in relation to the organic acid concentration: Fid-Bau Portal

Phytotoxicity of olive tree leaf compost in relation to the organic acid concentration

Manios, V.I. / Tsikalas, P.E. / Siminis, H.I. / Verdonck, O.

AbstractOlive tree leaves are one of the most abundant organic residues on the island of Crete. The objective of this study was to investigate the changes of phytotoxicity of olive tree leaves during the composting process in piles and correlate them with the changes of organic acid concentration. For this purpose, four piles were established with urea or ammonium nitrate as the nitrogen source. The piles were turned and sampled every 8 or 10 days. The organic compounds were extracted by ether from water extracts of the olive tree leaf samples and redissolved in water. The phytotoxicity of the ethersoluble organic compounds was determined by their inhibitory effect on the germination of lettuce seeds and was compared with the phytotoxicity of pure organic acids and sterile water. It was found that the organic acid concentration increased for approximately 2 weeks during the composting process and then decreased progressively. The phytotoxicity of both the ether-soluble organic extracts and the control solutions correlated inversely with the organic acid concentrations. However, it was higher in the olive tree leaf extracts than in the control solutions of pure formic, acetic, benzoic, salicylic, or tannic acid. These findings indicate that the phytotoxity consists of organic acids different from the control acids tested and/or other organic compounds.