- Part of the olive mill wastewater (OMW) generated in Mediterranean countries is disposed of on soil. This can, however, result in reduction of soil quality and plant growth. The underlying fate mechanisms and their effects on plant growth are still largely unknown. Our goal was to understand degradation of OMW organic matter (OMW-OM) in soil and its effect on seed germination. We hypothesized that OMW phytotoxicity decreases with degradation of its phenolic compounents. In a 60 day incubation study, we monitored 948;13C, extractable phenolic compounds and phytotoxicity of soil and soil extracts towards Lepidium sativum. Soil respiration was 2.5 times higher for OMW treated soil with two isolated respiration maxima and indicated degradation of up to XXXOM. The development of all investigated parameters indicated four phases of OMW-OM degradation: (i) degradation of easily degradable OMW-OM and transformation of phenolic compounds, (ii) intermediate suppression of phytotoxicity (iii) degradation of phytotoxic phenolic compounds and (iv), in contrast to our hypothesis, significant physical immobilization of phytotoxic compounds. Thus, environmental conditions during and after OMW disposal on soil should favour fast degradation OM in order to minimize their physical immobilization.
