An experiment comparing biochar effects on root, shoot, and fruit production in beans, tomatoes, and willows

Background/Question/Methods

Biochar (stable 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. However, the effects of biochar are variable across different biochar source materials, soils, plants and plant tissues, which renders it challenging to generalize and extrapolate across previous research. Our study investigated the effects of a single source of biochar (waste wood from a hazelnut orchard)on the different plant tissues (roots, shoots, and fruits) of three functionally distinct species: cherry tomatoes (Solanum lycopersicon var.), green beans (Phaseolus vulgaris var.), and hybrid willow saplings (Salix sp.). We used a constructed organic soil composed of peat moss and perlite that was fertilized and inoculated with mycorrhizae. Five biochar treatments were used: 0%, 2.5%, 7.5%, and 20% by weight, and a low inoculant treatment included at the 7.5% level. The response of tissues in different species was standardized using z-scores so that the degree of response to biochar could be directly compared among the three species.

Results/Conclusions

We found a highly significant positive relationship between the amount of biochar added to soil and total plant biomass in all three species. While no differences were evident in the response of total biomass among species, significant differences were evident in how individual tissues responded. In the tomato plants, root tissue did not increase significantly with biochar; response of root biomass in the other species was significant. The response of root:shoot ratio was also significantly different in all three species. Date of first flowering was earlier with increasing soil biochar only in beans, and percent bean germination increased significantly with biochar concentration. Control over the source of biochar and soil composition in this experiment expands evidence that biochar has different impacts on different plants and, in some cases, species-specific impacts on different plant tissues and other fertility measures. Our results were contrary to research that found inhibiting effects of biochar at levels comparable to our 20% treatment. This study was conducted in highly organic soil with hazelnut wood biochar; further research that controls soil type and biochar source are necessary to determine the extent to which these results are generalizable across sources of biochar, soil types and plants.