Assessment of Biochar Potential to Neutralize the Effect of Olive Mill Wastewater on Plant Growth in Alkaline Sand

The biotic-abiotic interactions are particularly challenging in alkaline conditions. Growth of plants is an ultimate indicator of such interactions. The on-land disposal of olive mill wastewater (OMW) negatively affects plant growth due to its high phytotoxic organic polyphenol content. Our previous study has shown that phenols may be successfully sorbed on biochar-one of the most promoted soil amendments. A greenhouse experiment was conducted to determine the combined and separate effect of OMW (applied at 50, 100 and 200 m(3) ha(-1)) and pinewood biochar (applied at 0.5, 2.5 and 5%) on the growth of wheat and green beans in an alkaline sand. Results showed that increasing OMW rate significantly suppressed wheat growth especially the above ground phytometrics, and that biochar addition did not significantly mitigate this effect. This was mainly attributed to unsuitable high pH growing conditions of the wheat, which was enhanced by application of OMW and biochar. In contrast, the lowest OMW only and 5% biochar only treatments positively affected bean phytometrics, though not statistically significant. A significant positive interaction was obtained in the bean total biomass when 2.5 and 5% biochar was applied on soil that received 100 m(3) ha(-1) OMW. Findings showed that pinewood biochar application at 2.5 and 5% enhanced tolerance of beans to OMW applied at 100 and 200 m(3) ha(-1) likely due to not only reduction of phenol toxicity but also due to increased available soil P and K.