Pyrolysis temperature has greater effects on carbon and nitrogen biogeochemistry than biochar feedstock when applied to a red pine forest soil

Authors: TOCZYDLOWSKI, ALAN - University Of Minnesota; SLESAK, ROBERT - Us Forest Service (FS); Venterea, Rodney - Rod; Spokas, Kurt

Submitted to: Forest Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/16/2023
Publication Date: 2/27/2023
Citation: Toczydlowski, A., Slesak, R., Venterea, R.T., Spokas, K.A. 2023. Pyrolysis temperature has greater effects on carbon and nitrogen biogeochemistry than biochar feedstock when applied to a red pine forest soil. Forest Ecology and Management. 534. Article 120881. https://doi.org/10.1016/j.foreco.2023.120881.
DOI: https://doi.org/10.1016/j.foreco.2023.120881

Interpretive Summary: Biochar is produced from burning wood or other organic material under low-oxygen conditions, in a process referred to as pyrolysis. When used as a soil amendment, biochar may improve soil properties and plant growth. However, most studies investigating biochar effects on soil nutrient cycling have been done in row-crops, with less information available in forest systems. Because biochar could be produced from large quantities of residual woody biomass that is typically unmerchantable due to its size or quality, there is an interest in the potential for biochar to improve forest soil health. In this study, we applied biochars created from black ash or balsam fir woody feedstock pyrolyzed at 350°C or 450°C to a nutrient-poor forest soil in a laboratory incubation. We measured gaseous and leachate fluxes to assess the influence of biochar on carbon (C) and nitrogen (N) cycling. We found a clear response to pyrolysis temperature with the lower temperature (350°C) biochar causing greater carbon dioxide (CO2) fluxes and leaching of dissolved N and organic C compared to unamended soil. In contrast, the higher temperature (450°C) biochar appeared to retain more N than the lower temperature biochar but had little impact on CO2 fluxes. The black ash feedstock also had greater C leaching than balsam fir. These results will be useful to scientists and land managers in evaluating the potential impacts of biochar amendment as a means of conserving nutrients in forest soils while protecting water and air quality.

Technical Abstract: The majority of studies evaluating effects of biochar on soil properties and plant responses have focused on agricultural soils, with limited focus on forested settings. There is increasing interest in applying biochar in forests because of the perceived benefits to soils and productivity, and because biochar could be produced from large quantities of residual woody biomass that is typically unmerchantable because of its size or quality. To test if findings from agricultural soils are applicable to forest soils, we applied biochars created from black ash or balsam fir woody feedstock pyrolyzed at 350°C or 450°C to a nutrient-poor forest soil in a laboratory incubation. To assess the influence of biochar on carbon (C) and nitrogen (N) cycling, we measured fluxes of carbon dioxide (CO2) and nitrous oxide (N2O), leaching of dissolved inorganic and total N and organic C, and post-incubation C and N soil chemistry. We found mixed effects, but a generally clear response to pyrolysis temperature. The lower temperature, 350°C biochar generally increased CO2 fluxes and had greater N and dissolved organic C leaching while the higher temperature, 450°C biochar seemed to adsorb and hold onto N and had little impact on CO2 fluxes. The black ash feedstock had greater C leaching than balsam fir, but responses were similar across all other metrics suggesting that woody feedstocks produce biochar with similar properties.