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

Wolfram Buss, Stina Jansson, Ondřej Mašek

Research output: Contribution to journalArticlepeer-review


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.
Original languageEnglish
Pages (from-to)960-967
JournalJournal of Cleaner Production
Early online date17 Oct 2018
Publication statusPublished - 1 Jan 2019

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