Biochar has positive but distinct impacts on root, shoot, and fruit production in beans, tomatoes, and willows

Biochar, a stable type of charcoal produced through anaerobic combustion of biomass, provides a mechanism of concurrently sequestering carbon and increasing soil fertility and food production. Positive relationships have been documented between biochar concentration in soil and plant growth and fertility. However, the effects of biochar are variable across different biochar source materials, soils, environments, plants, and plant tissues. This makes it challenging to compare and generalize findings across previous research. Our study investigated the effects of a single source of biochar (waste wood from a local hazelnut orchard), in a constructed organic soil inoculated with mycorrhizae, on the different plant tissues (roots, shoots, and fruits) of three functionally dis-tinct species: cherry tomatoes (Solanum lycopersicon var.), green beans (Phaseolus vulgaris var.), and willow saplings (Salix sp.). This experiment took place over the summer of 2021 and extended through the summer of 2022 for willows. Five levels of biochar amendment were assessed: a 0% control, 3%, 9%, and 26% by dry weight. A low inoculant treatment was also included at the 9% level. Plants were grown in fabric pots, rotated weekly, fertilized, and irrigated. We found a highly significant positive relationship between the amount of biochar added to the soil and total plant biomass in all species, with no significant difference in total biomass response among species. Fruit production increased with increased biochar addition in both beans and tomatoes. Tomatoes exhibited significant differences in response among plant tissues; in tomatoes fruit production and shoot biomass increased significantly with biochar, but root tissue did not. Bean germination suc-cess increased significantly with biochar concentration. Date of first flowering was earlier with increasing soil biochar in beans but not in tomatoes. Control over both sources of biochar and soil composition in this experiment enables us to conclude that biochar addition can have different impacts on different plants and, in some cases, species-specific impacts on different plant tissues and other measures of fertility. Our results are contrary to prior research that found inhibiting effects of biochar at levels comparable to our 26% treatment. Small differences in soil chemistry among treatments lead us to conclude that microbial interaction with biochar is an important factor explaining the positive impacts of soil biochar on plant fertility. It is important to note that our study was conducted in a highly organic soil with hazelnut wood biochar; further research that controls for soil type and biochar source is necessary to determine the extent to which findings of this study apply to other biochar sources in other soil types and for other species of plants