Biochar and Other Amendments to Enhance Tree Seedling Growth for Mine Revegetation

Biochar is the carbon-rich material remaining after pyrolysis (heating in a low oxygen atmosphere) of organic feedstocks. As a soil amendment, biochar has the potential to sequester heavy metals, improve soil water-holding capacity, and increase nutrient retention, thereby enhancing soil conditions to benefit plant growth. Thus, biochar can enhance the establishment and growth of plants for mine site revegetation. This was a preliminary greenhouse pot screening study with different amendments, to determine effects on soil and plants before initiating a full-scale on-site revegetation study. We evaluated the potential for biochar, along with agricultural lime and nutrient sources (biosolids or mineral fertilizer), to enhance the survival and growth of Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] seedlings in mine spoils from the Formosa mine Superfund site in southern Oregon. We made biochar by high temperature gasification of conifer softwoods, and applied it at 2.5% by weight to the spoil soil. The soil had an extremely low pH (~2.6). Addition of 0.5% or 1.0% lime (w/w) raised soil pH to 5.8 and 7.2, respectively. Increasing the soil pH and was necessary for seedling survival and growth, and decreased concentrations of heavy metals (e.g., Al and Cu) in the soil leachate. However, a high level of added nutrients (2%, vs. 0.5% or 0.25% w/w of biosolids or fertilizer) inhibited plant growth, especially at the higher pH. The addition of biochar enhanced seedling survival, root growth, water usage, and new tissue potassium concentration, at least in part by reducing the detrimental effects of high nutrients. This study indicates that biochar, along with lime and nutrients, can enhance early seedling growth in mine affected soils by improving soil physical and chemical characteristics.

Impact/Purpose

Past mining activities in the United States have left a legacy of heavy metal contaminated soils, which need to be cleaned up to allow for healthy plants on the site, and to prevent water and soil pollution. The EPA has regulatory authority, especially under Comprehensive Environmental Response, Compensation, and Liability Act (Superfund) to oversee cleanup of these sites; and responsibility to regions, states and local communities under the Office of Research and Development’s Safe and Healthy Community Research Program to develop new techniques to assist in this cleanup. Of special concern to EPA’s Region 10 is the Formosa mine superfund site in south-central Oregon, which has a large area of degraded soils where it is difficult to establish vegetation. This research was designed to determine if a newly developed technique, addition of biochar to soils, could assist revegetation efforts. Biochar is the carbon-rich material remaining heating of waste organic materials in a no, or low oxygen atmosphere, which has been shown to improve soil chemistry such as acidity (pH), tie up contaminants such as heavy metals, and improve soil characteristics favorable to plants such as water-holding capacity and fertility. We evaluated the potential for biochar made from conifers, along with agricultural lime and nutrient sources (biosolids or mineral fertilizer), to enhance the survival and growth of Douglas seedlings in mine spoils from the Formosa mine site. This study was a preliminary greenhouse screening of plants and a variety of combinations of amendments before initiating a full-scale on-site revegetation study. The soil had an extremely low pH (2.6), and addition of 0.5% or 1.0% lime raised pH to 5.8 and 7.2, respectively. The increase in pH decreased concentrations of heavy metals (e.g., Al and Cu) in the soil leachate, and was necessary for seedling survival and growth. However, a high level of added nutrients (2%, vs. 0.5% or 0.25%) inhibited plant growth, especially at the higher pH. Addition of biochar enhanced seedling survival, root growth, water usage, and new growth K concentration, at least in part by reducing the detrimental effects of high nutrients. This study demonstrated that biochar, along with lime and nutrients, can enhance early seedling growth in mine affected soils by improving soil physical and chemical characteristics, providing immediately useful information to alleviate a soil pollution problem in Region 10. More broadly, the study illustrated the potential for techniques developed under ORD’s biochar research program to enhance plant growth by improving soil chemistry, thus increasing the potential for success of vegetation reestablishment to degraded soils across the United States.

Citation

Olszyk, D., Mark G Johnson, M. Bollman, T. Shiroyama, J. Novak, AND D. Watts. Biochar and Other Amendments to Enhance Tree Seedling Growth for Mine Revegetation. Annual Meeting of society Entoxicology and chemistry, Toronto, Ontario, CANADA, November 04 - 07, 2019.