Biochar is a stable form of carbon produced by burning organic matter (usually wood) under low oxygen conditions. It can be used as a soil amendment to increase the fertilizer holding capacity in soils, making the fertilizers slowly available to the plants and preventing them from leaching into the ground water. It can also help to increase water retention in sandy soils to reduce leaching and provide more water to plants for a longer time. In addition, biochar has been shown to suppress soilborne pathogens and increase populations of beneficial soil microorganisms, making it a potentially great amendment to Florida’s sandy soils. Mixing biochar with compost increased plant productivity even more than the combination of biochar and mineral fertilizers in past research.
Blueberries are usually grown in Florida with pine bark fines added to the soil to increase the organic matter and lower soil pH needed for good blueberry growth. Pine bark fines will decompose with time, requiring replenishing every few years. Biochar is an option that may be used to replace some of the pine bark fines with a more stable, longer lasting soil amendment.
Researchers in Oregon tested potted blueberries grown in unamended sandy loam soil and soil amended with 10 or 20% by volume of biochar. The researchers also inoculated half the plants with Phytophthora cinnamomi, a common root rot organism, to see if biochar helped to overcome the soilborne pathogen. After 12 weeks, plants were evaluated for leaf area, root and top dry weight, and the soil was analyzed for microbial, chemical and physical characteristics.
Plants fertigated with a complete nutrient solution had the highest biomass and leaf area with soil amended with 20% biochar. Biochar improved soil aggregation and increased root colonization by ericoid mycorrhizal fungi by 54% to 94% compared to unamended soil with ≤ 10% colonization. Phytophthora infected plants were stunted with root rot, and soil amendments did not make a difference. From this experiment biochar looks promising to increase ericoid mycorrhizal fungi and reduce fertilizer needs but does not help to reduce Phytophthora root rot. Although biochar had an initial high pH, it did not impact the already low pH of the soil.
Amending Sandy Soil with Biochar Promotes Plant Growth and Root Colonization by Mycorrhizal Fungi in Highbush Blueberry. 2020. B.K. Sales, D.R. Bryla, K.M. Trippe, J.E. Weiland, C.F. Scagel, B.C. Strik, D.M. Sullivan. HortScience 55(3):353-361.