Experimental addition of olive mill waste compost in an old agroecosystem: identifying main shortterm vegetation responses

Olive mill wastewater (OMW) is the main residual product of olive processing and its disposal can represent a relevant environmental issue in Mediterranean countries. OMW is characterised by high pollutant load, salinity and phytotoxic levels of polyphenols, but also by a high amount of organic compounds and plant mineral nutrients. In this perspective, a technology named MATReFO was developed, with a final dry product easy to transport for commercial use. Here, we assessed the short-term effects of OMW and MATReFO applications on spontaneous vegetation in an old agroecosystem. Following a randomized block design soil was amended with different quantities of OMW or MATReFO and vegetation was sampled for 4 years after the treatments. Multivariate and univariate analyses of plant data showed that: (1) only high volume of MATReFO affected spontaneous vegetation, whereas OMW and low volume mixture addition did not determine significant effects; (2) plant species composition and abundance varied significantly among years and exhibited considerable variation over the study period, particularly with high volume of MATReFO; (3) vegetation dynamic had already undergone first steps of natural succession in control and almost all treatments. Our results revealed no negative effects of olive mill waste compost addition in plant community assemblage, since vegetation changes can be mainly related to the abandonment of soil tillage. Therefore, we can assert that OMW and MATReFO can be discharged in abandoned agroecosystems without short-term effects on natural vegetation.