Much of the research surrounding agricultural biochar application is still in its infancy and further experimentation is needed to solidify management recommendations, especially in terms of isolating soil and environmental interactions (Gelardi & Parikh 2021). Encouraging use also relies on developing the economic case for biochar, part of which may come from payments for the carbon it stores, but part of which may rely on other co-benefits. As one of those benefits, what about utilizing biochar to help manage nutrients?
To answer these broader scale questions, foundational research is quickly progressing to prove biochar as a filter for nutrients in soils and wastewater while removing carbon biomass from the waste streams and atmosphere.
What is Biochar?
Biochar is the product of heating forms of biomass to a certain temperature threshold under low-oxygen conditions, a process called pyrolysis (Amonette et al 2021). Biomass can include anything from lumber waste to grasses and manures, and the feedstock that is used help determine the characteristics of the resulting biochar product. The characteristics of chars are also impacted by the conditions under which they are made, including whether they have been treated before or after being made.
The Benefit of Biochar Adsorption
One of biochar’s most impressive features? Biochar contains numerous rings of highly stable carbon with “sticky” edges- meaning that different nutrients and metals are likely to be held and released by biochar edge sites (Figure 1). You might have heard of using activated charcoal in human cases of overdoses or poisoning, and biochar can act in a similar fashion within the soil and even in stormwater. These edge sites can pick up contaminants and hold them, which can be hugely beneficial in soil remediation from heavy metals. The question that remains, however, is whether biochar can act as a sponge for excess nutrients that are prone to leaching through the soil and contaminating waterways, and whether such a strategy could be feasible at scale.
Take phosphorous as an example. Phosphorous is essential to plant growth and is one of the most frequently utilized amendments for field crops- and extremely prevalent in dairy manure. While utilizing manure as a crop fertilizer provides a circular flow of nutrients back into the environment, the levels of nutrients present don’t always match the crop uptake in exact proportions. Manure as an amendment must be monitored carefully to avoid excess nutrients being released into the surrounding environment. Certain soil types, timing of applications, and runoff events can contribute to phosphates leaching into groundwater and surface water supplies. Excess phosphorus in water systems can cause algal blooms and subsequent eutrophication, where there is limited oxygen left for organisms within freshwater sources. Providing a material “trap” for these excess nutrients would reduce negative impact on the surrounding environment- especially water sources.
Managing these anion levels from amendments is a major research question to protect both natural resources and agricultural production, which is where biochar comes back into the picture. While biochar is not intrinsically suited to hold anions, they can be chemically modified to adsorb phosphates and other nutrients of interest through a method called “doping”.
Through work supported by WSU and WSDA Applied Bioenergy Research Program, WSU researchers Michael Ayiana, Aidan Garcia, Sohrab Haghighi Mood, Jean-Sabin McEwen, and Manuel Garcia-Perez are studying ways to dope biochar with a nitrogen-metal combination (N-Ca-, N-Fe-, and N-Mg-), in an effort to trap phosphates. While adding metal initially sounds off-putting, these metal elements — calcium, iron, and magnesium — are often essential plant micronutrients and are naturally occurring within soils.
Currently, their research shows that biochar doping with a nitrogen-metal combination creates phthalocyanine-like structures (figure 2). While the centers of the resulting compounds are highly stable and unlikely to pick up phosphate, the resulting edges of these compounds are well-suited to adsorb excess phosphate. The resulting doped biochars can potentially be used as a filter at two ends- within the processing of manure into an amendment to prevent the overapplication of phosphorous, and as a soil amendment to prevent further leaching. If successful, this could be another tool in the management of wastewater and other potential pollution sources to protect the downstream environment.
The potential for biochar as a remediation tool beyond its current uses is a big step forward not only for the environmental benefits, but also as another tool in the toolbox for agricultural sustainability. Keep watching for continued developments on the biochar front and more from the Applied Bioenergy Research Program.
Ayiania, M., A. Garcia, S. Haghighi Mood, J.S. McEwen, and M. Garcia-Perez. 2022. Novel Amorphous Carbons for the Adsorption of Phosphate: Part I. Elucidation of Chemical Structure of N-Metal-Doped Chars. ACS Omega 2022 7 (17), 14490-14504. Open Access Online Version
Amonette, J.E., J.G. Archuleta, M.R. Fuchs, K.M. Hills, G.G. Yorgey, G. Flora, J. Hunt, H.-S. Han, B.T. Jobson, T.R. Miles, D.S. Page-Dumroese, S. Thompson, K.M. Trippe, K. Wilson, R. Baltar, K. Carloni, C. Christoforou, D.P. Collins, J. Dooley, D. Drinkard, M. Garcia-Pérez, G. Glass, K. Hoffman-Krull, M. Kauffman, D.A. Laird, W. Lei, J. Miedema, J. O’Donnell, A. Kiser, B. Pecha, C. Rodriguez-Franco, G.E. Scheve, C. Sprenger, B. Springsteen, and E. Wheeler. 2021. Biomass to Biochar: Maximizing the Carbon Value. Report by Center for Sustaining Agriculture and Natural Resources, Washington State University, Pullman WA. Biomass to Biochar
Gelardi, D.L.; Parikh, S.J. Soils and Beyond: Optimizing Sustainability Opportunities for Biochar. Sustainability 2021, 13, 10079. Online Version
Smith MW, Dallmeyer I, Johnson TJ, Brauer CS, McEwen JS, Espinal JF, Garcia-Perez M: Structural analysis of char by Raman Spectroscopy: Improving band assignments through computational calculations from first principles. Carbon, 100, 2016, 678-692.
This is part of a series of posts highlighting work by Washington State University researchers through the Applied Bioenergy Research Program of the Agricultural Research Center at Washington State University, College of Agricultural, Human, and Natural Resource Sciences.