Has compost with biochar added during the process added value over biochar or compost to increase disease suppression?

Adding biochar at the onset of composting has proven to be beneficial for this process, and when added to the soil, this biochar-blended (BB) compost has outperformed biochar on soil quality but had a similar effect as the compost. Because soil quality gets more and more attention as an important tool for soil health, pot trials were conducted to evaluate the effect of compost and biochar alone, and biochar-blended (BB) compost on disease suppression. In addition, it was investigated whether the disease suppression was associated with changes in soil quality (chemical, physical and biological soil properties). The two selected bio-assays were Rhizoctonia solani (basal rot) on lettuce and potato cyst nematodes (PCN) on potato. Both compost and BB compost released mineral N and thus increased lettuce and potato yield but biochar did not. None of the amendments affected the susceptibly of lettuce leaves to basal rot. Compost suppressed PCN while biochar had no effect on PCN reproduction. Moreover, BB compost reduced the suppressing effect of compost. We suggest that the inhibitory effect of biochar blended in compost might be attributed to the fungal biomass which was not increased in the BB compost-amended soil compared to compost-amended soil, and/or the absorbance of suppressive compounds by the high surface area of biochar. Interestingly, all three amendments reduced the water evaporation from the soil surface, which can have important implications for drought stress of plants.