The way forward in biochar research: targeting trade‐offs between the potential wins

Abstract

Biochar application to soil is currently widely advocated for a variety of reasons related to sustainability. Typically, soil amelioration with biochar is presented as a multiple-'win' strategy, although it is also associated with potential risks such as environmental contamination. The most often claimed benefits of biochar (i.e. the 'wins') include (i) carbon sequestration; (ii) soil fertility enhancement; (iii) biofuel/bioenergy production; (iv) pollutant immobilization; and (v) waste disposal. However, the vast majority of studies ignore possible trade-offs between them. For example, there is an obvious trade-off between maximizing biofuel production and maximizing biochar production. Also, relatively little attention has been paid to mechanisms, as opposed to systems impacts, behind observed biochar effects, often leaving open the question as to whether they reflect truly unique properties of biochar as opposed to being simply the short-term consequences of a fertilization or liming effect. Here, we provide an outline for the future of soil biochar research. We first identify possible trade-offs between the potential benefits. Second, to be able to better understand and quantify these trade-offs, we propose guidelines for robust experimental design and selection of appropriate controls that allow both mechanistic and systems assessment of biochar effects and trade-offs between the wins. Third, we offer a conceptual framework to guide future experiments and suggest guidelines for the standardized reporting of biochar experiments to allow effective between-site comparisons to quantify trade-offs. Such a mechanistic and systems framework is required to allow effective comparisons between experiments, across scales and locations, to guide policy and recommendations concerning biochar application to soil.

Substitution of peat moss with softwood biochar for soil-free marigold growth

“…The neutral to alkaline pH of BCs and their liming potential (Glaser et al 2002;Hass et al, 2012;Van Zwieten et al, 2010) means that BC substitution for peat can increase pH beyond optimum for plant growth in potting media (Fryda and Visser, 2015;Steiner and Harttung, 2014;Vaughn et al, 2013). Explicit evaluation of BC effects on substrate pH and plant performance provides a basis to improve design of BC-based substrates and inform trade-offs in this application of BC (Jeffery et al, 2015).…”

Fourfold Increase in Pumpkin Yield in Response to Low-Dosage Root Zone Application of Urine-Enhanced Biochar to a Fertile Tropical Soil

“…While most biochar applications described so far consisted of homogenous spreading and ploughing over the whole field plot, conservative farming practices propose to apply soil amendments in a more concentrated fashion and close to the roots, e.g., in the hoe basins or rip lines where cultivation occurs [33][34][35]. Blackwell et al [36] tested banded biochar application on dry land wheat production and concluded that the banding application of biochar at low application rates of 1 t·ha…”

Biochar for Soil Improvement: Evaluation of Biochar from Gasification and Slow Pyrolysis

“…The filtering and adsorption qualifications are likely to involve different pore sizes and pore distributions than the water holding capacity where water must also be released again. As stated by Jeffery et al [47] not all functionalities can be obtained at the same time and choices have to be made for different benefits.…”