Unexplored potential of novel biochar-ash composites for use as organo-mineral fertilizers

Abstract

Application of wood ash on forest and agricultural soils can provide nutrients and increase soil pH, however, it changes the soil chemistry rapidly and temporarily, often resulting in reduced plant growth and potassium leaching. Biochar from woody materials are nutrient poor and need nutrient enhancement prior to soil application. In this study, spruce residues were mixed with spruce/pine ash in different ratios (0-50%) to produce biochar-ash composites at 450°C. The biochar yield (ash-free basis) increased by 80-90% with the addition of 50% ash due to catalytic biochar formation. Consequently, nearly half the amount of wood is needed to produce the same amount of (ash-free) biochar. Mineral release was moderated in the composites compared to pure ash, demonstrated by a lower electric conductivity and % available K content (a factor of 2.5-4.4 lower than in wood ash). Furthermore, the % available chromium content, which is a key potentially toxic element in wood ash, decreased by a factor of 50-160. Soil application of biochar-ash composites decreases the risk of Cr toxicity, salinity stress and leaching of K in soil substantially compared to ash application. Biochar-ash composites are a novel product with vast unexplored potential for use in forestry and agriculture.

How biochar works, and when it doesn't: A review of mechanisms controlling soil and plant responses to biochar

“…Controlled release biochar‐fertilizer combinations can be produced from low‐nutrient biomass mixed with mineral or organic nutrients before pyrolysis and/or organic nutrients after pyrolysis, or by composting to enrich with nutrients (Buss et al, 2019, 2020; Dong et al, 2019; Hagemann, Joseph, et al, 2017; Schmidt et al, 2015) and these can be effective at low application rates when applied in a band near the seed/plant (Qian et al, 2014; Schmidt et al, 2015; Yao et al, 2015; Zheng et al, 2017).…”

Ash from Jerusalem artichoke and biopreparations enhance the growth and physiological activity of sorghum and limit environmental pollution by decreasing artificial fertilization needs

“…This ash may contain toxic substances absorbed by the trees during their long period of growth (Santalla et al, 2011;Vassiliev et al, 2013). Buss et al (2019) indicated that the application of wood ash could provide nutrients and increase the pH of forest soil and it could also temporarily change its chemistry within a relatively short period of time. Jagodzinski et al (2018) demonstrated the positive effect of ash from burnt wood on Lemna minor L. development, whereas Romanowska-Duda et al (2019c) showed the stimulating influence of sorghum ash on the development and physiological activity of Lemnaceae.…”

Enhancing Natural Cycles in Agro-Ecosystems to Boost Plant Carbon Capture and Soil Storage

“…A significant part of basalt comprises alkali and earth alkaline metals (Table 2) that also have the potential to catalyse biochar formation. Therefore we expect a similar effect by incorporating basalt into the biomass before pyrolysis, which in addition increases the nutrient content of biochar, providing further benefits for plant growth and carbon sequestration 63,82 .…”

“…Biochar and basalt application mainly affects the CEC in acidic soils through an increase in soil pH, although the direct provision of negatively charged surface sites may also have a positive influence [58][59][60] . Enrichment of biomass with inorganic nutrients before pyrolysis or application of biochar with nutrient-rich organic or inorganic materials offers slow-nutrient release potential that provides synergistic improvements on plant growth 46,[61][62][63][64] .…”