Biochar: Improving Chemical and Physical Properties of Horticultural Substrates

Biochar, the product of thermal pyrolysis, is a carbon-rich substance with numerous horticultural uses and potential applications. Biochar has been researched extensively as a carbon biosequestration material and soil builder in landscape and agronomic areas. The potential benefits of biochar in horticultural cropping systems have not been fully investigated.  Studies were conducted to: identify potential organic materials with regional availability that could be converted into biochar; evaluate biochar materials for nutrient supplying/retention properties when amended to container substrates; determine effect on biochar incorporation on substrate pH; determine effect on substrate physical properties; and observe the effect on substrate stability over time. Biomass materials evaluated included rice hulls, wood from various sources, and switch grass.  Biochar materials were incorporated into peat and pine bark-based substrates at 5%, 10%, and 15% (by vol.) ratios.  Initial physical properties were determined and plant growth trials were conducted to evaluate plant growth and performance in all biochar substrate treatments. Regardless of material, pyrolysis time affected the biochar properties, resulting in different potential benefits when amended in peat and pine bark substrates.  Biochar had greatly increased cation exchange capacity compared to pre-pyrolysis materials. The incorporation of biochar was found to improve air-filled porosity in peat-based (greenhouse) substrates and, if processed finely (small) enough, could increase container capacities in bark-based (nursery) substrates.  Processing of materials before pyrolysis was the important step in determining particle size of the biochar, thereby changing its affect on substrate physical properties.  Biochar materials show no degradation during short term (one season) greenhouse or nursery crop production.  Research suggests that biochar can be a viable avenue for organic biomass utilization while maintaining or improving substrate chemical and physical properties. Fertility studies and long-term crop production evaluations are needed to assess the full potential of these materials in horticultural substrates.