The Impact of Sewage-Sludge- and Olive-Mill-Waste-Derived Biochar Amendments to Tomato Cultivation

This study elucidated the impact of sewage-sludge (SS) and olive-mill-waste (OMW) biochar amendments to soil using tomatoes as a test crop. Four treatments were evaluated: the "control" with no biochar amendment, two SS biochar treatments with the addition of 10 t/ha and 25 t/ha, respectively, and an OMW biochar treatment with the addition of 25 t/ha. Higher yields were observed in both SS biochar treatments, providing evidence that biochar acts as a plant bio-stimulant. Biochar application had positive impacts on carbon sequestration and soil structure. The uptake of heavy metals by all plant parts was very low, indicating that biochar is an appropriate product for land application. Biochar dose and type induced changes in the composition due to the different unique species and biodiversity of microbial communities. Venn diagrams revealed that the majority of the identified taxa were shared among the treatments, and only a small proportion of them were unique in bulk soil between treatments. In the rhizosphere, the OMW-biochar-treated plants showed a higher number of unique taxa. Microbiota structure plays a major role in the stimulation of plant growth; however, further research is needed to understand the impact of these shifts in the functioning of agroecosystems.