Biochar Application: Essential Soil Microbial Ecology

By T. Komang Ralebitso-Senior and Caroline H. Orr

Biochar Application: Essential Soil Microbial Ecology outlines the cutting-edge research on the interactions of complex microbial populations and their functional, structural, and compositional dynamics, as well as the microbial ecology of biochar application to soil, the use of different phyto-chemical analyses, possibilities for future research, and recommendations for climate change policy.

Biochar, or charcoal produced from plant matter and applied to soil, has become increasingly recognized as having the potential to address multiple contemporary concerns, such as agricultural productivity and contaminated ecosystem amelioration, primarily by removing carbon dioxide from the atmosphere and improving soil functions.

Biochar Application is the first reference to offer a complete assessment of the various impacts of biochar on soil and ecosystems, and includes chapters analyzing all aspects of biochar technology and application to soil, from ecogenomic analyses and application ratios to nutrient cycling and next generation sequencing. Written by a team of international authors with interdisciplinary knowledge of biochar, this reference will provide a platform where collaborating teams can find a common resource to establish outcomes and identify future research needs throughout the world.

• Includes multiple tables and figures per chapter to aid in analysis and understanding
• Includes a comprehensive table of the methods used within the contents, ecosystems, contaminants, future research, and application opportunities explored in the book
• Includes knowledge gaps and directions of future research to stimulate further discussion in the field and in climate change policy
• Outlines the latest research on the interactions of complex microbial populations and their functional, structural, and compositional dynamics
• Offers an assessment of the impacts of biochar on soil and ecosystems

• Language: English
• Publisher: Elsevier Science
• Release date: May 7, 2016
• ISBN: 9780128034361

T. Komang Ralebitso-Senior

T. Komang Ralebitso-Senior is a Senior Lecturer in Forensic Science in the School of Pharmacy and Biomolecular Sciences at Liverpool John Moores University, UK. She has studied at the City University of New York, the University of Natal (South Africa), and Vrije Universiteit Amsterdam. She held post-doctoral positions at the BioMEMS Laboratory of Nanyang Technological University, Singapore, and the NERC Centre for Ecology & Hydrology, Oxford. Komang is a STEM Ambassador and member of the Society for Applied Microbiology and the International Society for Microbial Ecology.

Book preview

Biochar Application

Essential Soil Microbial Ecology

Editors

T. Komang Ralebitso-Senior

Caroline H. Orr

Teesside University, Middlesbrough, United Kingdom

Table of Contents

Cover image

Title page

Copyright

Dedication

Contributors

Foreword

Acknowledgments

Chapter 1. Microbial Ecology Analysis of Biochar-Augmented Soils: Setting the Scene

Overview

Biochar

Biochar and Its Applications

Biochar as Habitat for Soil Organisms

Soil Biota Response to Biochar

Policy Guidelines and Requirements for Biochar Application

Summary

Chapter 2. Feedstock and Production Parameters: Effects on Biochar Properties and Microbial Communities

Biochar Characteristics and Key Determining Parameters

Influence of Biochar on Microbial Communities

Conclusions and Outlook

Chapter 3. Biochar Effects on Ecosystems: Insights From Lipid-Based Analysis

Background

Extracting Lipids and Production of Fatty Acid Methyl Esters

Making Sense of PLFA: Analytical Approach and Interpretation of PLFA Data

Compositional and Structural Insights From PLFA

Biochar as Habitat

Linking Who to What: Functional Insights From PLFA

Misuse of PLFA

Conclusions

Chapter 4. DGGE-Profiling of Culturable Biochar-Enriched Microbial Communities

Introduction

The Case Study

Chapter Conclusions and Future Recommendations

Chapter 5. Next-Generation Sequencing to Elucidate Biochar-Effected Microbial Community Dynamics

Introduction

Anthropogenic Biochar

Biochar and Soil Properties

The Microbial Diversity in Biochar

Biochar and the Amazonian Dark Earth: A Case Study

Future Research

Chapter 6. Examining Biochar Impacts on Soil Abiotic and Biotic Processes and Exploring the Potential for Pyrosequencing Analysis

Introduction

Abiotic Processes

Biotic Processes

Metagenomic Sequencing Technologies

Conclusions

Chapter 7. Elucidating the Impacts of Biochar Applications on Nitrogen Cycling Microbial Communities

Introduction

The Microbial Nitrogen Cycle

Biochar’s Physicochemical Properties Affecting Soil Microbial Nitrogen Transformations

Biochar Effects on Soil Microbial Nitrogen Cycling

Knowledge Gaps and Future Research

Global Impact of Biochar on Soil Nitrogen Cycling

Chapter 8. Microbial Ecology of the Rhizosphere and Its Response to Biochar Augmentation

Introduction

An Illustrative Study

Conclusion

Chapter 9. Potential Application of Biochar for Bioremediation of Contaminated Systems

Introduction

Environmental Application of Biochar in Heavy Metal-Contaminated Systems

Environmental Application of Biochar in Systems Impacted by Organic Pollutants

Environmental Application of Biochar to Groundwater Systems

Recommendations for Further Research

Chapter 10. Interactions of Biochar and Biological Degradation of Aromatic Hydrocarbons in Contaminated Soil

Introduction

PAH Degradation

Biochar and Atrazine Interactions

Conclusions, Outlook, and Future Research Needs

Chapter 11. A Critical Analysis of Meso- and Macrofauna Effects Following Biochar Supplementation

Role of Fauna in Soil Ecosystem Structure and Function

Fauna Effects on Biochar: Bioturbation and Persistence

Biochar Effects on Soil Fauna

Interactions Between Biochar and Fauna

Chapter 12. Summation of the Microbial Ecology of Biochar Application

Book Rationale

Methodological State of the Art

Book/Knowledge Paucities and Recommendations for Future Work

Summary

Index

Copyright

Elsevier

Radarweg 29, PO Box 211, 1000 AE Amsterdam, Netherlands

The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, UK

50 Hampshire Street, 5th Floor, Cambridge, MA 02139, USA

Copyright © 2016 Elsevier Inc. All rights reserved.

No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions.

This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein).

Notices

Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary.

Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility.

To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein.

British Library Cataloguing-in-Publication Data

A catalogue record for this book is available from the British Library

Library of Congress Cataloging-in-Publication Data

A catalog record for this book is available from the Library of Congress

ISBN: 978-0-12-803433-0

For information on all Elsevier publications visit our website at https://www.elsevier.com/

Publisher: Candice Janco

Editorial Project Manager: Marisa LaFleur

Production Project Manager: Vijayaraj Purushothaman

Designer: Matthew Limbert

Typeset by TNQ Books and Journals

Dedication

To our families

Contributors

P. Barakoti,     Teesside University, Middlesbrough, United Kingdom

A.O. Bayode,     Teesside University, Middlesbrough, United Kingdom

S. Behrens,     University of Minnesota, Minneapolis, MN, United States and BioTechonology Institute, St. Paul, MN, United States

F.S. Cannavan,     University of São Paulo, Piracicaba, São Paulo, Brazil

T.R. Cavagnaro,     The Waite Research Institute, The University of Adelaide, SA, Australia

R. Chintala,     Nutrient Management & Stewardship, Innovation Center for U.S. Dairy, Rosemont, IL, United States

L.F. de Souza,     University of São Paulo, Piracicaba, São Paulo, Brazil

X. Domene

Autonomous University of Barcelona, Bellaterra, Barcelona, Spain

Centre for Ecological Research and Forestry Applications (CREAF), Bellaterra, Barcelona, Spain

C.J. Ennis,     Teesside University, Middlesbrough, United Kingdom

A.-M. Fortuna,     North Dakota State University, Fargo, ND, United States

M.G. Germano

University of São Paulo, Piracicaba, São Paulo, Brazil

Brazilian Agricultural Research Corporation, Embrapa Soybean, Londrina, Paraná, Brazil

Y. Gong,     Nankai University, Tianjin, China

R. Gurav,     Nankai University, Tianjin, China

N. Hagemann,     University of Tüebingen, Tüebingen, Germany

J. Harter,     University of Tüebingen, Tüebingen, Germany

H. Lyu,     Nankai University, Tianjin, China

F.M. Nakamura,     University of São Paulo, Piracicaba, São Paulo, Brazil

E.-L. Ng,     Future Soils Laboratory, Melbourne, VIC, Australia

C.H. Orr,     Teesside University, Middlesbrough, United Kingdom

J. Pickering,     Teesside University, Middlesbrough, United Kingdom

S. Prior,     Teesside University, Middlesbrough, United Kingdom

T. Komang Ralebitso-Senior,     Teesside University, Middlesbrough, United Kingdom

T.E. Schumacher,     South Dakota State University, Brookings, SD, United States

G. Soja,     AIT Austrian Institute of Technology GmbH, Tulln, Austria

C. Steiner,     University of Kassel, Witzenhausen, Germany

S. Subramanian,     South Dakota State University, Brookings, SD, United States

J. Tang,     Nankai University, Tianjin, China

S.M. Tsai,     University of São Paulo, Piracicaba, São Paulo, Brazil

Foreword

Biochar is charcoal made from biomass and used as a soil amendment. In late 2014, Elsevier asked me to review a book proposal on biochar by Komang Ralebitso-Senior and Caroline Orr. I had been aware of the potential of biochar to improve agricultural productivity, clean up contaminated land, and promote carbon sequestration to reduce the impact of climate change. As always my advice to investigators was to provide evidence in support of the claims. It seemed to me that a lot had already been written, but few books covered in depth the hard scientific evidence backing the case for biochar use. My dialogue with the authors on their proposal suggested that they had the capacity to produce just the type of book needed for scientists to evaluate the evidence base for the biological activity. If it passed that test, and field trials were positive, then policymakers would be in a better place to recommend various biochar formulations as a means to protect the planet and promote food security. Komang and Caroline have been up to the challenge of producing such a book, and the scientific and agricultural communities now have a very useful volume to consider the evidence.

I have spent a career in research largely trying to establish evidence that might be useful to develop policy for public and environmental good. This is in contrast to curiosity–driven activity, which might also be termed blue sky research. The reality is that innovation, which is the process of translating an idea or invention into goods or services for the public good or for which people will pay commercially, is critical in both paths. As Coordinator of the OECD Co-operative Research Programme for Biological Resource Management for Agricultural Sustainability from 1989 to 2006, I was continually inviting topics for bi-national research collaboration and international workshops. Always the challenge was to select innovative ideas, often applying the latest technologies from widely varying topics. For example, these ranged from the use of earth observation in precision agriculture, to the use of the latest DNA/RNA probes to identify relevant biological activity in soil. Many were in the context of climate change, which is having so much impact on the planet, its biota, and its people. Biochar is a potentially innovative topic and product, and can be investigated using innovative technologies such as DNA/RNA probes.

Innovation can be clouded by false claims. While working in the United States and in other countries such as India, I became aware of the snake oil salesman who would try to peddle microbial inoculants to improve agricultural production. Most could be dismissed because of lack of evidence but occasionally evidence was produced for the value of a preparation. These included rhizobia to stimulate nitrogen fixation in legumes, and bacteria and fungi that can control pests and diseases, some of the inoculants having been genetically modified. Most importantly, however, molecular markers became increasingly the system of choice to identify establishment and effectiveness. Caroline and Komang’s book effectively collates some of the latest scientific investigations, including molecular markers, on biochar action in the environment and will provoke much discussion; I hope it is read widely.

Jim Lynch, OBE,     Distinguished Professor of Life Sciences, University of Surrey

Acknowledgments

First, we would like to acknowledge those who contributed directly to this manuscript: the teams of authors who helped to make our idea a reality and added to the strength of the book; and Professor Jim Lynch, who gave us his time to discuss the need for a policy statement and then agreed generously to write the Foreword.

Several anonymous reviewers endorsed our book proposal and informed some of our decisions, helping to shape the book into its current form. We were also helped by researchers who could not contribute to the manuscript, but pointed us in the direction of people who could.

We are grateful to Elsevier for giving us this opportunity to showcase our analysis of state-of-the-art biochar research, its future direction, and policy requirements. In particular, Marisa LaFleur is acknowledged gratefully for her friendly, task-oriented, and supportive professionalism.

Throughout the process we have been supported by our colleagues at Teesside University who: allowed us to pick their brains on the publishing process and shared their experiences of its inherent joys and pitfalls; made time to help develop our blog video clip; and, generally, provided us with a Go for it! attitude.

This book has also happened as a result of contributions from our student researchers Abayomi Olaifa, Pratima Rai, Daniel Dancsics, Emma Phillips, Stephen Anderson, Shaun Prior, Christopher Schroeter, Sean Lindsay, Joe Russell, Jodie Harris, and Paul Wilkinson. Their enthusiasm for our biochar research has helped focus our minds and kept the wheels going. Furthermore, their research would not have been possible without funding from the Teesside University Research Fund, Department for Learning Development Students as Researchers, and Society for Applied Microbiology Students into Work schemes.

Of course, there are many people who supported us academically before we had the idea for this book but whose encouragement has helped shape our careers. Specifically, Komang would like to thank Professor Eric Senior, Professor Henk van Verseveld (RIP), and Dr Wilfred Röling (RIP). Caroline would like to thank Professor Stephen Cummings, Dr Julia Cooper, Professor Jennifer Ames, Dr Lynn Dover, and Dr Andrew Nelson.

Thankfully, there is more to our lives than being academics and we are lucky enough to be surrounded by many fantastic people who remind us of, and nurture, this balance when we need it. We will never be able to communicate fully our gratitude to you, our family and friends, for your support this year, and always especially our parents: Malebitso and Alex (RIP), Jean and Michael.

Our final acknowledgment is reserved for our husbands, Eric Senior (and Our Two Ks) and Mark Dunkley. Thank you, mainly, for tolerating us, particularly when we come home late, get distracted with emails at weekends and holidays, and expect you to act as sounding boards during moments of ranting. Your unconditional love and support helps make us what and who we are.

Chapter 1

Microbial Ecology Analysis of Biochar-Augmented Soils

Setting the Scene

T. Komang Ralebitso-Senior,  and C.H. Orr     Teesside University, Middlesbrough, United Kingdom

Abstract

Biochar has a recognized potential to address multiple contemporary concerns by effecting efficient carbon sequestration, enhanced agricultural productivity, and improved environmental restoration/reclamation. For contaminated land the high surface area and cation exchange capacity enable sorption of both organic and inorganic molecules/pollutants and so reduce their mobility and increase their bioavailability. As most environmental biotechnologies are underpinned by complex interacting microbial populations (multispecies gene pools), there is a need for specific focus on their functional, structural, and compositional dynamics following biochar application. Emerging research, which employs microbial ecology tools, such as culture-based analysis, community fingerprinting, quantitative or real-time polymerase chain reaction, and next-generation sequencing, has increased our understanding of the responses of microbial communities in soil ecosystems following addition of different biochars, re feedstock and production conditions, on a range of sites subjected to various application regimes/ratios. Therefore the principal objective of this book is to showcase the seminal and cutting-edge studies on the (molecular) microbial ecology of historical and contemporary biochar applications to soil. This introduction, specifically, aims to link the subsequent chapters to ensure coherence, logical progression, and continuity. Therefore the narrative considers the effects of biochar on microbial and mesofaunal populations in pristine, agronomic, and contaminated sites as determined by phenotypic, phylogenetic, and functional analyses that target whole communities and their different biomolecules. The chapter also attempts to set the scene for biochar policy and legislation requirements toward efficient and consistent control and management of its intended and unintended impacts on ecosystem services both in the short and long term.

Keywords

Agriculture; Bioremediation; Carbon sequestration; Microbial ecology; Policy; Soil biodiversity

Outline

Overview 2

Biochar 2

Terra Preta 4

Contemporary Biochar and Physico-/Biochemical Characteristics 4

Biochar and Its Applications 5

Climate Change Mitigation 5

Agriculture 7

Bioremediation 15

Biochar as Habitat for Soil Organisms 16

Soil Biota Response to Biochar 19

Microfauna 19

Meso-/Macrofauna 23

Policy Guidelines and Requirements for Biochar Application 24

Summary 31

References 32

Overview

Surpassing energy production and water provision, carbon sequestration, to slow the momentum of inimical climate change, is now the single greatest challenge facing the scientific community. Of the various sequestration options, charcoal production, to stabilize photosynthetically fixed carbon, and its subsequent application to soil (biochar), is destined to make a significant contribution particularly with its additionalities of waste reduction and energy production. Together with carbon sequestration, significant economic benefits can be gained through ecosystem restoration, including contaminated land remediation and improved plant productivity, by enhanced fertilizer efficacy, with small farmers in developing countries set to benefit most from this climate-smart agriculture (Cernansky, 2015).

The importance of harnessing carbon can be gauged readily by recognizing that between the 1850s and 2000 carbon loss from the soil organic pool totaled 78  ±  12 gigatonnes (Gt) while natural fire biochar redressed the balance by 35% at most.

According to the UK Environment Agency, contaminated land accounts for >57,000  ha in England and Wales alone while the African continent is blighted by 63  million hectares. Current bioremediation strategies, such as land-farming/pump-and-treat/semipermeable and permeable reactive barriers, can be enhanced considerably by biochar as a vehicle for biosupplementation, biostimulation, and bioaugmentation. With the unprecedented global interest in the use of biochar as an environmental management tool, this book aims to showcase the cutting-edge studies and findings on the (molecular) microbial ecology of historical and contemporary biochar applications to soil.

Biochar

Biochar, sometimes termed pyrochar, is the carbon-rich, solid by-product obtained from the carbonization of biomass, such as wood, manure, or leaves, heated to temperatures between 300°C and 1000°C under low (preferably zero) oxygen concentration. This process is known as pyrolysis (Lehmann, 2007; Lehmann and Joseph, 2009; Verheijen et al., 2010), which, typically, gives three products: liquid (bio-oil); solid (biochar); and gas (syngas) with the yield of each varying dramatically depending on the pyrolysis process (slow, fast, and flash) and conditions (ie, feedstock, temperature, pressure, time, heating, and rate) (Fig. 1.1). In particular, biochar production has been reported to decrease with increasing temperature (IEA, 2007 cited in Spokas et al., 2009).

Figure 1.1  Summary of thermal conversion processes in relation to common feedstocks, typical products, and potential applications ( Sohi et al., 2010 ).

Hydrochar differs from typical biochars as it is produced by liquefaction or hydrothermal carbonization, which results in an increased H/C ratio and decreased aromaticity (Lehman and Joseph, 2015). Furthermore, selections of feedstock and pyrolysis conditions have been considered as prime determinants of biochar properties and thus its efficacy in a wide range of contexts and/or ecosystems. Consequently, biochars vary widely and profoundly not only in their nutrient contents and pH but also in their organochemical and physical properties (Lehmann et al., 2011; Novak et al., 2009). Therefore it is crucial to consider the intended application prior to production to determine feedstock selection and pyrolysis protocol to produce bespoke biochar to address specific environmental concerns (Novak et al., 2009). According to Lehmann and Joseph (2009), the term biochar should not to be confused with agrichar as the latter could be derived from charred plastics or nonbiological materials. Also, although the production of biochar often mirrors that of charcoal, it is distinguished from it by its intended use in soil treatment, carbon storage, or filtration of percolating soil water (Lehmann and Joseph, 2009).

Biochar addition may affect soil biological community composition, as demonstrated for the biochar-rich Terra Preta soils in the Amazon (Grossman et al., 2010), and has been shown to increase soil microbial biomass (Liang et al., 2010, cited in Lehmann et al., 2011). Independent of possible microbial abundance increases, the net effects on soil physical properties depend on the interactions of the biochar with the physicochemical characteristics of the soil and other determinant factors such as the local climatic conditions and the biochar application regime (Verheijen et al., 2010). Also, parallel with soil enrichment, biochar may pose a direct risk to soil fauna and flora (Lehmann et al., 2011).

Terra Preta

The application of biochar to improve agricultural soils is not novel since it has been practiced for centuries. Terra Preta—Brazilian oxisols, anthropogenically modified by the inhabitants of the Amazonia region, also known as "Terra Preta de Indio,"—contains a high concentration of charcoal presumably through deliberate application by pre-Columbians and Amerindians (Kim et al., 2007) rather than the incidental presence of charred remains from forest clearing and burning (Novak et al., 2009; Verheijen et al., 2010). These anthrosols have been reported to persist over many centuries despite the prevailing humid tropical conditions and rapid mineralization rates (Lehmann et al., 2002), showing enhanced nutrient concentrations compared to surrounding soils. They have also been characterized to support a wider genetic agrobiodiversity relative to other soil types in the region (Atkinson et al., 2010).

These soils have attracted considerable interest with an extensive literature providing results on long-term carbon sequestration and microbial activity. The rich soils improve crop growth and are high in nutrients such as phosphorus and calcium (Warnock et al., 2007). Comparing microorganisms from Terra Preta fields to normal soils has facilitated diversity and abundance (Grossman et al., 2010) study although microbial community identification presents challenges with approximately only, as yet, 5% being cultured. In a study by Kim et al. (2007) a taxonomic cluster analysis was used to show the differences between two locations of Terra Preta and a preserved forest. The clusters highlighted site differences as well as species abundance changes with depth and distance. Both Kim et al. (2007) and Grossman et al. (2010) reported the dominance of Verrucomicrobium sp., Proteobacteria, and Acidobacterium sp. in the carbon-supplemented soil. In response to these results, Zhou et al. (2009) produced a table of microorganisms identified in Karst Forest by restriction fragment length polymorphism (RFLP) analysis and showed the widespread occurrence of these species.

Contemporary Biochar and Physico-/Biochemical Characteristics

It is well established that the substrates and pyrolysis parameters for producing different biochars determine their physico- and biochemical properties and thus their effects on the indigenous microbial populations (see also Chapter 2). Also the effects will be site and application ratio specific.

Feedstock determines the final chemical composition while process temperature, in particular, determines the surface area, pore size/volume/distribution, sorption, and partitioning of the biochar. Some of the substrates, production conditions, and properties of the generated biochars have been summarized in Table 2.1.

Generally, high-temperature pyrolysis (>550°C) produces biochars with high surface areas (>400  m²  g−¹) (Downie et al., 2011; Keiluweit et al., 2010), increased aromaticity and therefore high recalcitrance (Singh and Cowie, 2008), and good adsorption properties (Lima and Marshall, 2005; Mizuta et al., 2004). In contrast, low-temperature pyrolysis produces higher yields but the products are, potentially, more phytotoxic although they may improve soil fertility because of the stability of the aromatic backbone and increased functional groups, which provide sites for nutrient exchange (Gai et al., 2014; Joseph et al., 2010). Together with temperature, pyrolysis time is an important variable since the two determine cation exchange capacity as has been deliberated widely in the literature (eg, Lee et al., 2010).

Although generally accepted, the underpinning mechanisms of the different responses of biochar application relative to feedstock, production parameters/conditions, receiving ecosystem, methods of physicochemical, biochemical, and microbial ecology analyses, and measurement of plant biomass, yield, or output, are yet to be elucidated fully.

Biochar and Its Applications

Together with the rapidly growing population, an increasing number of global threats, such as food security because of declining agricultural production, periodic fuel crises, water scarcity, and climate change, have motivated biochar applications with several ongoing research initiatives seeking solutions for immediate implementation. Magnitude and urgency dictate multi-/cross-disciplinary efforts of numerous technologies and approaches.

Climate Change Mitigation

The increasing atmospheric concentrations of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) are of major concern when considering future climates. For all three, cycling, production, consumption, or storage are linked substantially with soils (Gärdenäs et al., 2010). Anthropogenic activities (eg, fossil fuel emission, industry) and natural phenomena (such as carbon cycle, organic matter mineralization) are the major contributors of these biogenic greenhouse gases and are considered to be the main influence on radiative forcing and perturbation of global climate.

Annually, plants are thought to harness 15–20 times the volume of CO2 emitted by fossil fuel, although about half of this is returned immediately to the atmosphere through respiration with approximately 60  Gt retained in new plant growth (about 45% (w/w) of planet biomass is carbon) (Sohi and Shackley, 2010). It has been estimated that globally, soils hold more organic carbon (1–100  Gt) than the atmosphere (750  Gt) and the terrestrial biosphere (560  Gt). Additionally, the flux of CO2 from soil to the atmosphere has been reported to be in the region of 60  Gt  C  year−¹, which results mainly through microbial respiration because of soil organic matter mineralization (Verheijen et al., 2010). Therefore a net sink of atmospheric CO2 was a principal consideration for combining pyrolysis with soil biochar application to retain photosynthetically fixed CO2 (Lehmann, 2007).

Biochar, returned to the soil, conveys both quality benefits and, potentially, carbon sequestration (Lehmann, 2007; Spokas et al., 2009). It has been estimated that about half of plant biomass carbon can be converted through pyrolysis into chemical forms that are biologically and chemically recalcitrant. Feedstock and pyrolysis temperature can, however, determine carbon retention (Lehmann, 2007). Consequently, carbon, trapped as biochar, increases its recalcitrance and has the potential to exist for hundreds to thousands of years or possibly longer (Spokas et al., 2009; Verheijen et al., 2010), thus increasing carbon input relative to microbial respiration output and thus climate change mitigation (Steinbeiss et al., 2009; Verheijen et al., 2010).

Several investigations have indicated that biochar additions not only lead to a net sequestration of CO2 but also may decrease emissions of CH4 and N2O (Lehmann, 2007; Sohi and Shackley, 2010). Although the atmospheric concentrations of CH4 (1.74–1.87  ppm) and N2O (321–322  ppb) are substantially lower than that of CO2 (385  ppm), their impacts on global warming on a mass basis are approximately 25 and 298 times greater, respectively, over a 100-year timeframe (US EPA, 2011 cited in Liebig et al., 2012). In a study by Rondon et al. (2005) it was observed that emission of N2O from soybean plots was reduced by 50% and CH4 was suppressed fully following acidic soil biochar supplementation (20  mg  ha−¹) in the Eastern Colombian Plains (Spokas et al., 2009). Similarly, Yanai et al. (2007) observed an 85% reduction in N2O production of rewetted soils with 10  wt% biochar compared to control soils possibly because of lower nitrification resulting from the higher C:N ratio or lower carbon quality (Lehmann, 2007). More work is, however, required to determine the effects of biochar on the soil nitrogen cycle and the associated greenhouse gas emissions.

The microbial ecology of biochar application in the context of climate change potential is explored in Chapters 7, 8, and 11 with a focus on greenhouse gas emissions or mitigation caused by soil application. In general the contradictory findings on whether biochar augmentation contributes to or alleviates NOx gas production in agricultural contexts highlight the need for further global studies. To date, most published literature on this has focused on biochemical analyses with microecophysiology-based studies as indicated in Table 1.1.

Agriculture

There is real potential for biochar to close an agronomic circle through enhanced yields (microbial stimulation in the rhizosphere), reduced energy outputs (less fertilizer application), minimized carbon emissions (carbon sequestration), and decreased irrigation demands (improved soil moisture-holding capacity). The partial and/or full realization of these must be informed by elucidating, critically, the basic tenets of how soil microbial communities respond to biochar augmentation.

Biochar has been considered as a potential approach to develop more sustainable agricultural systems, together with addressing global food security and reducing greenhouse gas emissions as major concerns in agricultural management (H functional groups that can serve as nutrient exchange sites after oxidation (Novak et al., 2009).

The central quality of biochar that makes it attractive as a soil supplement is its highly porous structure, which varies from <0.9  nm in nanopores to >50  nm in macropores, which improves water retention and increases soil surface area (Atkinson et al., 2010; Sohi et al., 2009). The study by Liang et al. (2006) on sandy soil biochar inclusion demonstrated specific surface area increase (×4.8) relative to adjacent soil. Typically, sandy soils have a limited specific surface area (0.01–0.1  m²  g−¹) compared to clayey soils (5–750  m²  g−¹) so their water and nutrient retention capacities are low (Atkinson et al., 2010). A crucial factor here is the ability of biochar to adsorb (and transport) nutrients, which are retained commonly in soil by adsorption to minerals and organic matter (Lehmann, 2007). As with biochar, the cation exchange capacity (CEC) of soil increases in proportion to the amount of organic matter. Since biochar has a higher surface area, greater negative surface charge, and greater charge density than other soil organic matter, it has the capacity to adsorb cations to a greater extent. The potential CEC of biochar has also been recorded to increase with increased temperature (Lehmann, 2007). Additionally, biochar has shown to contribute directly to nutrient adsorption, thereby decreasing nutrient leaching and, consequently, increasing nutrient use efficiency with resultant higher crop yield.

Table 1.1

Examples of microbial ecology techniques used to study biochar-impacted ecosystems as of January 2016