Biochar coating potential to suppress storage diseases in carrots and potatoes (CHARCOAT)

Can biochar coating decrease diseases severity during potato and carrot storage? Biochar is a carbon rich material used to improve soils’ quality. Recently, biochar has also been found to suppress plant diseases caused by foliar and soil borne pathogens. Here, we tested if biochar coating could reduce storage diseases of carrots and potatoes. During storage, potatoes and carrots are vulnerable to different microorganisms that can cause a variety of post-harvest diseases. The losses due to storage diseases could reach up to 40 % of volume of the harvested carrot and potato. To test the potential of biochar as a disease suppressor, we performed laboratory, middle- and large-scales trials. In the laboratory, we studied the best way to apply biochar as a coating for carrots and potatoes. Further, in a middle scale facility, we tested the effectiveness of biochar coating to diminish disease incidence under stressed environmental conditions. After gathering knowledge about biochar use and its potential to control storage diseases, we ran a trial in commercial potato store. Finally, we performed a germination test with coated potatoes in soils infected with potato soilborne diseases. Furthermore, we discussed the bottlenecks and environmental-social impacts on of using biochar coating in the potato industry. Initial studies in laboratory demonstrated that biochar needs to be crushed to a particle size <700 µm to stick to the surface of potatoes. Without mechanical treatment, only 4 % of the biochar particles passed this mesh size in a sieving test. The adhering biochar was not lost during storage and was easily removed by washing. Somewhat higher weight loss of non-coated potatoes during storage (at 22°C) may indicate that the coating had a kind of insulation effect. A pilot study of carrots stored at about 8°C demonstrated the well-known fact that industrial washing of carrots makes them susceptible to fouling. Coating washed carrots with biochar was quite efficient to avoid fouling, but not as efficient as not washing them. Coating of unwashed carrots did not decrease the weight loss of carrots during storage or increase the number of edible carrots after about 3 months of storage. In the industrial scale trial, we observed that after 6 months of storage, potatoes coated with biochar had a significant lower proliferation of potato diseases, increasing in 10 % the total amount of the Quality 1 potatoes when compared to the un-coated potatoes. However, in our germination experiment we did not see a clear effect of biochar coating in the germination of potatoes in soils with potentially infected with diseases. For practical application of biochar in vegetable industry, many challenges need to be addressed. The use of biochar as fine particles increases the amount of dust which may imply a risk of explosion, and which has consequences for both environment and human health and may also affect water quality. StandardBio biochar contains a low concentration of polycyclic aromatic hydrocarbon (PAH), 1.2 mg of total PAH /kg of dry biochar. This value is at least three times lower than the limit values stipulated for sustainable production of biochar of the European biochar certificate. However, the concentration of PAH can change according to the applied substrate to make the biochar, and production conditions during pyrolysis. Thus, package plants planning to apply biochar for storage purpose need to have a careful plan for the use of biochar.