Biochar and compost amendments promote yield in specialty crops

There is growing evidence for the positive impact of compost and biochar as soil amendments. However, the effect observed has varied widely, depending on the crop species and the particular biochar formulation. Few studies have evaluated more than one crop × biochar-based amendment combination.

To further address this question, we conducted a series of experiments with several crop species grown in the greenhouse and/or in the field, comparing the impact on crop yield and quality of several biochar-based soil amendments, including raw biochar, co-composted biochar, and biochar admixed with compost, using more than one compost type.

The incorporation of compost, co-composted biochar, and a combination of compost and biochar led to an enhancement in the productivity of sweet basil and strawberries. The effects differed according to the type of compost, biochar, and crop. Two basil cultivars and three composts amended with biochar were used in a greenhouse study. Specific combinations of particularly co-composted biochar led to increased biomass output compared to controls. The same amendments to the soil did not markedly influence the phytochemical content of sweet basil cultivated in either field or greenhouse, suggesting that the quality of the final product was unaffected. Co-composted biochar led to biomass increases for both basil cultivars in a field-based experiment, but the increases were not identical, suggesting a genetic component to the plant's response to the soil amendments. A strawberry experiment conducted in the greenhouse found that the average mass of single berries from plants grown with commercially produced compost plus 10% biochar was higher compared to several other treatments, particularly when it was co-composted. In a potato-based experiment, preliminary field trial data showed that co-compost amendments were the only amendment that increased potato crop production, but this was demonstrated only in fertilized split-plots.

Additional experiments will need to be conducted to evaluate the mechanisms responsible for the observed enhancement in yield for these various crop × biochar-based amendment combinations.