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

We synthesized 20 years of research to explain the interrelated processes that determine soil and plant responses to biochar. The properties of biochar and its effects within agricultural ecosystems largely depend on feedstock and pyrolysis conditions. We describe three stages of reactions of biochar in soil: dissolution (1–3 weeks); reactive surface development (1–6 months); and aging (beyond 6 months). As biochar ages, it is incorporated into soil aggregates, protecting the biochar carbon and promoting the stabilization of rhizodeposits and microbial products. Biochar carbon persists in soil for hundreds to thousands of years. By increasing pH, porosity, and water availability, biochars can create favorable conditions for root development and microbial functions. Biochars can catalyze biotic and abiotic reactions, particularly in the rhizosphere, that increase nutrient supply and uptake by plants, reduce phytotoxins, stimulate plant development, and increase resilience to disease and environmental stressors. Meta-analyses found that, on average, biochars increase P availability by a factor of 4.6; decrease plant tissue concentration of heavy metals by 17%–39%; build soil organic carbon through negative priming by 3.8% (range −21% to +20%); and reduce non-CO2 greenhouse gas emissions from soil by 12%–50%. Meta-analyses show average crop yield increases of 10%–42% with biochar addition, with greatest increases in low-nutrient P-sorbing acidic soils (common in the tropics), and in sandy soils in drylands due to increase in nutrient retention and water holding capacity. Studies report a wide range of plant responses to biochars due to the diversity of biochars and contexts in which biochars have been applied. Crop yields increase strongly if site-specific soil constraints and nutrient and water limitations are mitigated by appropriate biochar formulations. Biochars can be tailored to address site constraints through feedstock selection, by modifying pyrolysis conditions, through pre- or post-production treatments, or co-application with organic or mineral fertilizers. We demonstrate how, when used wisely, biochar mitigates climate change and supports food security and the circular economy. © 2021 The Authors. GCB Bioenergy published by John Wiley & Sons Ltd.

Joseph S.1, 2, 3, 4 , Cowie A.L.3, 5 , Van Zwieten L. , Bolan N.7, 8, 9 , Budai A.10 , Buss W.11 , Cayuela M.L.12 , Graber E.R.13 , Ippolito J.A.14 , Kuzyakov Y. 15, 16, 17 , Luo Y.18 , Ok Y.S.19 , Palansooriya K.N.19 , Shepherd J.20 , Stephens S.21 , Weng Z.22, 23 , Lehmann J.24
Blackwell Publishing Ltd
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  • 1 School of Materials Science and Engineering, University of NSW, Kensington, NSW, Australia
  • 2 Institute of Resources, Ecosystem and Environment of Agriculture, and Center of Biochar and Green Agriculture, Nanjing Agricultural University, Nanjing, China
  • 3 School of Environmental and Rural Science, University of New England, Armidale, NSW, Australia
  • 4 ISEM and School of Physics, University of Wollongong, Wollongong, NSW, Australia
  • 5 New South Wales Department of Primary Industries, Armidale, Parramatta, NSW, Australia
  • 6 New South Wales Department of Primary Industries, Wollongbar, NSW, Australia
  • 7 Cooperative Research Centre for High Performance Soil (Soil CRC), Callaghan, NSW, Australia
  • 8 School of Agriculture and Environment, The University of Western Australia, Perth, WA, Australia
  • 9 School of Engineering, College of Engineering, Science and Environment, Callaghan, NSW, Australia
  • 10 Norwegian Institute of Bioeconomy Research, Division of Environmental and Natural Resources, Ås, Norway
  • 11 Research School of Biology, Australian National University, Canberra, ACT, Australia
  • 12 Department of Soil and Water Conservation and Waste Management, CEBAS-CSIC, Murcia, Spain
  • 13 Institute of Soil, Water and Environmental Sciences, The Volcani Center, Agricultural Research Organization, Rishon LeTzion, Israel
  • 14 Department of Soil and Crop Sciences, Colorado State University, Fort Collins, CO, United States
  • 15 Department of Soil Science of Temperate Ecosystems, Dept. of Agricultural Soil Science, University of Göttingen, Göttingen, Germany
  • 16 Agro-Technological Institute, RUDN University, Moscow, Russian Federation
  • 17 Institute of Environmental Sciences, Kazan Federal University, Kazan, Russian Federation
  • 18 Institute of Soil and Water Resources and Environmental Science, Zhejiang Provincial Key Laboratory of Agricultural Resources and Environment, Zhejiang University, Hangzhou, China
  • 19 Korea Biochar Research Center, APRU Sustainable Waste Management Program & Division of Environmental Science and Ecological Engineering, Korea University, Seoul, South Korea
  • 20 University of Edinburgh School of Geosciences, Edinburgh, United Kingdom
  • 21 New South Wales Department of Primary Industries, Parramatta, NSW, Australia
  • 22 School of Agriculture and Food Sciences, The University of Queensland, St. Lucia, QLD, Australia
  • 23 Department of Animal, Plant & Soil Sciences, Centre for AgriBioscience, La Trobe University, Melbourne, VIC, Australia
  • 24 Soil and Crop Sciences, School of Integrative Plant Science, Cornell University, Ithaca, NY, United States
carbon sequestration; GHG mitigation; heavy metals; priming effect; resilience; rhizosphere processes; soil carbon
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