Biochar-assisted Remediation of Contaminated Soils Under Changing Climate

Soil contamination with heavy metals like Cr, Co, Cu, Ni, Mn, Cd, Pb, and Zn is becoming a main problem across the globe especially in developed countries. Globally, it has become a serious threat to human health and ecosystem integrity. applying amendments like phosphate compounds, liming materials, clay minerals, coal fly ash, organic composts, metal oxides, and biochar to heavy metals contaminated soil is considered one of the most promising in-situ remediation techniques. Biochar has become one of the most attractive research hotspots as a result of its special properties along with its important role in the climate change, global biogeochemical cycle and environmental system.

This book will summarize recent progresses in understanding (a) metal-biochar interactions in soils, (b) potential risks associated with biochar amendment and (c) application of biochar for the remediation of HM polluted soils. In addition, research gaps and future directions in understanding biochar-metal interactions in soils will also be explored.

• Enables readers to understand the most recent developments surrounding metal-biochar interactions in soils and their impact on agricultural productivity
• Provides the latest statistics and literature review regarding the role of biochar in remediation of heavy metals polluted soils
• Examines the global status of heavy metals polluted soil

• Language: English
• Publisher: Elsevier Science
• Release date: Apr 19, 2024
• ISBN: 9780443215636

Book preview

Preface

The unwanted changes in the global climate and the environment are the main concerns of the present generation. Nothing is permanent because all these alterations are inevitable. Yet, why are we so worried by the variations happening in the global climate? The predicted rise in the occurrence of extreme climate events such as salinity, drought, temperature, and floods are threatening agricultural production and food security globally. In 2050 the population will reach nine billion, and this will a mammoth task for our fragile food production system, which is facing an enormous challenge from depleting natural resources and the cruelty of climate change calamities. It has been predicted that if our planet becomes 2.0°C warmer in average temperature, this will lead to a reduction in cereal grain production of more than 20%–40%, particularly in Asia and Africa. On one side the average temperature is rising, while on the other side we must upgrade our food system to run fast more than double—70% more food to meet the demands of the increased population. These immense tasks can be partially solved by biochar amendments because its utilization has already improved crop productivity, soil structure, storing nutrients, and water. Its application protects plants from the adverse effects of heat, drought, diseases, and pollution. Biochar provides habitat for soil microbial communities. It is imperative that long-term sustainable development strategies should be adopted by developed countries in particular and by developing countries in general. This book therefore finds various proposed solutions in tackling climate change, which are environment friendly.

Chapter 1

Biochar for soil health improvement in the present context of climate change: a reality or fantasy

Upasana Sahoo¹, Sagar Maitra¹, Akbar Hossain², D.T. Santosh³, Suprava Nath¹, Masina Sairam¹, Lalichetti Sagar¹, Jagadish Jena⁴, Sarthak Pattanayak⁵, Harun I. Gitari⁶ and Esmaeil Rezaei-Chiyaneh⁷,    ¹Department of Agronomy and Agroforestry, Centurion University of Technology and Management, Paralakhemundi, Odisha, India,    ²Division of Soil Science, Bangladesh Wheat and Maize Research Institute (BWMRI), Nashipur, Dinajpur, Bangladesh,    ³Research Centre for Smart Agriculture, Centurion University of Technology and Management, Paralakhemundi, Odisha, India,    ⁴Department of Agronomy, Faculty of Agricultural Sciences, Siksha ‘O’ Anusandhan Deemed to be University, Bhubaneswar, Odisha, India,    ⁵Krishi Vigyan Kendra, Odisha University of Agriculture and Technology, Puri, Odisha, India,    ⁶School of Agriculture and Enterprise Development, Kenyatta University, Nairobi, Kenya,    ⁷Department of Plant Production and Genetics, Faculty of Agriculture, Urmia University, Urmia, Iran

Abstract

Population across the globe is increasing at an alarming rate and is projected to reach 9.8 billion by the year 2050. At the same time, food demand for the increasing population has been increasing. Therefore it is important to increase crop yield per unit area of soil, since soil is a limited resource. As a result, the rapid human population growth coupled with increasing consumption is placing exceptional force on soils through the intensification of agricultural production. Several earlier findings already reported that the intensification of agricultural practices caused unmanageable soil degradation through loosing of soil organic matter, erosion, acidification, contamination by heavy metals, salinization, loss of genetic diversity, and also excessive use of inorganic amendments leading to the release of various greenhouse gases. The continuous degradation of soils ultimately threatens the production of food for the increasing population as well as cause environmental harm. The global society must not be shortsighted by focusing solely on the near-immediate to find a solution for improving soil fertility and productivity in intensive agricultural systems by enhancing the physio-biochemical properties of soils. Biochar, a soil amendment has already been evidenced as a potentially cost-effective and environmentally friendly carbonaceous soil resource. It is functioning over a long period for increasing soil water retention, soil aggregation, harmonizing soil pH, reducing soil bulk density, and also improving microbial activities under the changing climate. The current chapter focuses on the prospects of biochar as one of the potential cost-effective and environmentally friendly soil organic amendments in the intensive agricultural system under the changing climate.

Keywords

Biochar; increasing population; intensive agriculture; soil health; changing climate; agricultural soil science; soil science; environmental pollution; agronomy discipline; environmental science; agricultural science; agronomy; climate change; plant physiology; ecology

Outline

Outline

1.1 Introduction 2

1.2 Climate change impacts on soil properties 3

1.2.1 Major components of climate change which affect soil properties 3

1.2.2 Climate change impacts on soil physical properties 4

1.2.3 Climate change impacts on soil chemical properties 5

1.2.4 Climate change impacts on soil biological properties 6

1.3 Use of biochar in agriculture 7

1.4 Role of biochar on carbon sequestration and greenhouse gas emission 9

1.4.1 Biochar as a carbon sink: mechanisms and potential for long-term carbon sequestration 9

1.4.2 Assessing the environmental benefits and sustainability of biochar as a carbon sequestration strategy 9

1.5 Biochar for soil amendment 10

1.5.1 Biochar as an amendment in soils with physical constraints 10

1.5.2 Biochar as an amendment in acid soils 10

1.5.3 Biochar as an amendment in alkaline soil 11

1.5.4 Biochar as an amendment in nutrient-deficient soil 11

1.5.5 Biochar as an amendment in salt-affected soil 11

1.5.6 Biochar as an amendment in metal-contaminated soil 12

1.6 Impacts of biochar on soil physicochemical and biological properties 13

1.6.1 Physical properties 13

1.6.2 Soil chemical properties 14

1.6.3 Biological properties 14

1.7 An insight into the use of biochar versus fantasy 15

1.8 Conclusions 16

References 16

Further reading 33

1.1 Introduction

The prime concern of present-day agriculture is the reduction of climate change (CC) impacts. In this regard, it is essential to mitigate greenhouse gasses (GHGs) emissions leading to global warming and CC (Sagar et al., 2022); however, there is no decline recorded as it was 50 Gt CO2-eq/year in 2017 (IPCC, 2018). Instead of providing much emphasis on the reduction of GHGs emission to the atmosphere through carbon, there is hardly any significant impact in this regard (Chen et al., 2022; IPCC, 2019). The carbon dioxide removal (CDR) technologies should be set perfectly for the next few decades (Tisserant and Cherubini, 2019). There are several CDR technologies, but biomass conversion into biochar is well-thought-out as an effective measure (Fuss et al., 2018; Woolf et al., 2010). Biochar is a good input considered for soil amendment (Smith, 2016). Further, biochar has the potential for CDR and it is assumed that it may reduce 0.65 and 35 Gt CO2-eq/year (Tisserant and Cherubini, 2019). The worldwide CDR potential of biochar is assessed to range from 0.65 to 35 Gt CO2-eq/year (Tisserant and Cherubini, 2019).

Biochar is a valuable input that is not only considered as a CDR technology, but it has multifaceted benefits such as influencing soil health, reducing environmental pollution (Fischer et al., 2018; Lehmann et al., 2021) and crop productivity (Jeffery et al., 2017; Cornelissen et al., 2018; Sykes et al., 2019; Vijay et al., 2021). Biochar amendment has the potential to accentuate the CO2 flux resulting in lower GHGs emission (Mukherjee and Lal, 2013; Ashiq et al., 2020). In nutrients-deficient soil, the impacts of biochar in the enhancement of crop yield are more prominent (Laghari et al., 2015; Keller et al., 2023) in comparison to fertile soils (Hussain et al., 2017). Haefele et al. (2011) recorded 16%–35% yield enhancement of crops by biochar application in Philippines and Thailand. Vaccari et al. (2011) reported up to a 30% increase in durum wheat yield by the application of woodland biochar in the Mediterranean region. Moreover, it has several benefits on soil properties and the environment, which can further be investigated. An enhanced burden on agricultural systems because of fast urbanization and increasing population has drastically influenced soil health and fertility (Asabere et al., 2018; Brevik et al., 2020). The overincreasing food need has also led to the intensive use of chemical inputs, causing significant GHGs emissions. In this context, biochar, the multifunctional carbon material, can be explored to address the issues and concerns for improving soil health with a target to mitigate the ill effects of CC (Vijay et al., 2021; Nepal et al., 2023). The chapter analyzes the myth of biochar application to crop fields for soil health improvement under the consequences of CC influencing soil health.

1.2 Climate change impacts on soil properties

The CC and agriculture are completely interrelated, and various climatic factors especially influence the soil properties and impact on several progressions and functions in soil which are related to food and nutritional security as well as agricultural sustainability. The CC refers to changes in climatic phenomena like temperature, rainfall amount, rainfall frequency, occurrence and withdrawal, fluctuations in sea levels, fluctuations in the concentration of gases in the atmosphere, etc., for more than a decade which occur due to human activities (IPCC, 2007). Among these components, some affect the soil health and its properties.

1.2.1 Major components of climate change which affect soil properties

The following subsections present the important abiotic factors affecting soil properties.

1.2.1.1 Carbon dioxide

The CO2 concentration increased from 386 to 389 ppm in 2009, which was 38% higher than the preindustrial levels (270 ppm). The atmospheric carbon dioxide also gets affected due to the decreasing carbon sinks and continuous growth of emissions (Butler and Montzka, 2019).

1.2.1.2 N deposition

There was a wide variation in N2O content in the atmosphere which was 322 ppm in 2009 and reached 600 ppm in 2018 (Anjali and Dhananjaya, 2019).

1.2.1.3 Temperature

Global temperatures can increase from 1.1°C to 6.4°C during the present time which can lead to an increase in the temperature of the earth due to the infrared radiation passing through the atmosphere (IPCC, 2007).

1.2.1.4 Rainfall

An increase in global temperature makes the atmosphere warmer and thus, leads to an increase in water vapors in the atmosphere by decreasing the soil moisture content by 4% per degree Fahrenheit increase in temperature (IPCC, 2007).

1.2.2 Climate change impacts on soil physical properties

Soil physical properties are one of the important factors that need a greater focus with the advancements in agriculture and crop production. The composition and concentration of soil also get disturbed by the alterations in soil organic carbon accumulation, soil penetration potential, mobility of gases, water and nutrients, certain microbial activities, and ultimately, crop yield (Rimal and Lal, 2009; Horel et al., 2015; Abdul et al., 2021a,b; Abid et al., 2021; Adnan et al., 2020; Adnan et al., 2018a,b, 2019; Ahmad et al., 2019, 2022; Akbar et al., 2020; Akram et al., 2018a,b; Ali et al.2022).

1.2.2.1 Soil texture

Soil texture is a consistent characteristic of soil; however, due to aberrations in climatic aberrations, the sensitivity of the soil and the textural features get influenced. The shrinking and swelling of soil are directly related to the number of wetting and dry cycles, and this creates crakes in soil. The loosening of the soil due to the loss of textural properties increases the water flow speed which ultimately decreases the filtering capacity of the soil leading to the draining of nutrients from the soil profile. The intensive precipitation followed by frequent droughts is a regular occurrence; then the texture of the soil gets majorly disturbed, leading to the loss of intrinsic properties of soil (Bormann, 2012; Al-Zahrani et al., 2022; Amanullah et al., 2021; Amanullah, 2017; Amanullah, 2018a,b; Amanullah et al., 2020; Amir et al.2020; Amjad et al., 2020, 2021).

1.2.2.2 Soil structure

The mechanical disturbances in the soil impact the holding capacity between soil particles and soil aggregates, which ultimately affects the soil structure. The change in quantity and pattern and intensity of rainfall with varying temperature imbalances, the soil structure makes it rigid and tough for the cultivation of crops. Severe rain and runoff influence soil structure (Varallyay, 2010), as the aggregates are destructed (Singh et al., 2011; Anam et al.2021; Arif et al., 2020; Ashfaq et al., 2021). The agronomic practices adopted under changing climatic conditions may affect the biological activity and microbial functions leading to damage to soil structure (Singh et al., 2011; Athar et al., 2021; Atif et al., 2021; Aziz et al., 2017a,b).

1.2.2.3 Bulk density

The soil texture and composition of soil organic matter (SOM) are reliant on and they majorly influence the bulk density. The reduction of SOM content because of enhanced atmospheric and soil temperature or soil loss increases the bulk density. This increase in bulk density creates compaction in soil and decreases porosity and restricts root growth (Davidson and Janssens, 2006; Singh et al., 2011; Baseer et al., 2019; Bayram et al., 2020; Bukhari et al., 2021). Bulk density also gets affected by the temperature regimes and moisture changes due to climatic aberrations. The alterations in bulk density influence the hydrological properties leading to decreased microbial activity.

1.2.2.4 Soil water availability

The availability of soil water is vital for the flourishing of plants and it is dependent on soil processes (Jarvis, 2007; Chang et al., 2021; Chao et al., 2022; Chen et al., 2021; Deepranjan et al., 2021; Depeng et al., 2018; EL Sabagh et al., 2022; Emre et al., 2021). The soil water availability is influenced by rainfall patterns and the quantity of dry spells influencing water retention and infiltration rate enabling the proper functioning of the soil ecosystem (Singh et al., 2011).

1.2.3 Climate change impacts on soil chemical properties

The chemical body of any soil type represents the quality of soil, thereby predicting yield and directing the crop management operations. The different factors, namely, soil pH, cation exchange capacity (CEC), soil salinity, and nutrient availability influence the chemical properties of the soil; however, with climatic aberrations, the chemical properties get severely impacted (Ghulam et al., 2021; Gopakumar et al., 2020; Guofu et al., 2021; Habib et al., 2017; Hafeez et al., 2021; Hafiz et al., 2018, 2020a,b; Hafiz et al., 2016, 2019).

1.2.3.1 Soil pH

Soil acidification occurs due to the leaching of basic cations with increased precipitation. The mobility of toxic metals results in the reduction of basic cations (Brinkman and Sombroek, 1999) regardless if the soil is with proper draining facilities or well-structured or intense rainfall-receiving soil. The content of exchangeable H+ ions in the soil increases because of scanty rain, which thereby increases the salt content. During the wet season, salts get dissolved and diluted with deep percolation leading to an increase in soil pH (Stavi et al., 2021).

1.2.3.2 Cation exchange capacity

The CEC is an important component of soil health, and it determines the retaining of calcium, magnesium, and potassium, and induces control of toxic cations, namely, aluminum and manganese. An elevated temperature enhances the decomposition and decreases the SOM affecting the CEC. The CEC has a relation with the SOM content. Further, the low-activity clay soils lead to the increased leaching of basic cations which also is affected because of heavy rain (Weil and Magdoff, 2004).

1.2.3.3 Soil salinity

Global warming causes rapid glacial melting leading to an enhanced rise in sea level and also excess rainfall as well as flood and submergence causing harm to crop fields. The consequences of an increased temperature led to a rise in sea levels and this increased the salinity problem of crop fields in the coastal ecosystem (Varallyay, 2010). An enhanced temperature upsurges evapotranspiration ultimately affecting the potential of salt leaching due to rainfall scarcity (De Paz et al., 2012). The CC influences the accumulation of salts and causes salinization and this increase in salinization will rapidly increase in the next 20 years (IPCC, 2013). The resultant phenomena ultimately enhance soil salinity problems during the last three decades (Okur and Orçen, 2020; Haider et al., 2021; Hamza et al., 2021; Haoliang et al., 2022; Hesham and Fahad et al., 2020; Huang et al., 2021; Hussain et al., 2020).

1.2.3.4 Nutrient cycle and availability

The rise of temperature, variation in rainfall, and atmospheric N deposition because of CC influence on the N cycle (Weil and Magdoff, 2004). An enhancement of heat due to CC facilitates ammonia volatilization. Extremely hot weather and abnormality in rainfall enhance rhizospheric temperature and influence on soil moisture regime, which impact on the nutrient uptake by plants and the growth of plants. Under soil moisture deficit conditions, may cause soil erosion (Lal, 2012; Ibad et al., 2022; Ibrar et al., 2020, 2021; Ihsan et al., 2022; Ikram et al., 2021; Ilyas et al., 2020; Iqra et al., 2020; Irfan et al., 2021) and nutrient uptake are reduced under thermo-stress and drought (Fahad et al., 2017). In legumes, biological N fixation is hampered under drought (Athar and Ashraf, 2009). Further, drought may disturb the nutrient diffusion and mass flow of nutrients. The excess rain may cause soil erosion and nutrient draining from the topsoil (Zougmore et al., 2009; Jabborova et al., 2021a,b; Jan et al., 2019). Excessive rain also causes submergence and hypoxia, leading to various nutrient deficiencies and nitrogen loss in the form of denitrification (Grzyb et al., 2021; Kamran et al., 2017; Khadim et al., 2021a,b; Khan et al., 2021; Khatun et al., 2021).

1.2.4 Climate change impacts on soil biological properties

The soil microorganisms contribute a lot, as they consume GHGs and they intermediate the carbon turnover. The biological activities in the soil are greatly dependent on the microbial quotient.

1.2.4.1 Soil organic matter

The SOM consists of various complex materials with living and/or latent microorganisms (Weil and Magdoff, 2004). Under the changing climate, the presence of SOM in the soil is disturbed. SOM influences soil properties and various functions. It contributes as a source of carbon and nitrogen. It also controls P and S cycles in soil. It supports the habitation of soil microorganisms and fauna. SOM influences soil structure, soil moisture retention capacity, and hydraulic properties (Haynes, 2008).

1.2.4.2 Soil carbon and C:N ratio

The heat and intermittent rain influence the activities of microorganisms causing the depletion of C:N ratio (Lal, 2004). However, raised atmospheric CO2 enhances the water use efficiency of plants. The scanty rain causes loss of biomass and vegetation and exposes the soil to sunlight. Potentially mineralizable carbon and nitrogen, and mineralizable SOM act as interfaces between autotrophic and heterotrophic microbes (Gregorich et al., 1994). However, mineralizable SOM is beneficial to measure soil health under C as it impacts nutrient cycling.

1.2.4.3 Soil respiration

Soil respiration is a biological parameter as it is related to SOM present in the soil. Under CC, particularly in elevated temperatures soil respiration is altered, influencing the global C cycle (Wixon and Balser, 2009). The timing of rain has a great impact on soil respiration.

1.2.4.4 Soil microbial biomass

Soil microbes are the living component of SOM and are well-thought-out as a labile C pool in soils (Saha and Mandal, 2009). However, soil microorganisms are greatly influenced by SOM and SOC which are impacted adversely by the CC (Haynes, 2008).

1.2.4.5 Enzyme activity

Soil enzyme activity changes the plant–soil systems such as nutrient cycling and soil biology. These factors integrate both the presence of soil microorganisms and the physicochemical soil properties and respond to variations in soil management (Garcia-Ruiz et al., 2009). The microbial enzyme activity also gets affected and stimulated due to the alterations in the carbon inputs by plants and elevated CO2.

1.3 Use of biochar in agriculture

Pyrolyzed product of plant biomass, so-called biochar is reported to have numerous advantages and uses in agriculture for its sustenance, that is, C-sequestration (Lehmann et al., 2006), which improves soil fertility (Spokas et al., 2012), helps in reestablishing degraded land (Beesley et al., 2011), reduces GHGs emission (Cayuela et al., 2014), enhances ecosystem service (Halldorsson et al., 2015), and acts as an antidote for some of the major factors hindering global food security (Smith and Gregory, 2013). Out of the total biochar produced, 33% of biochar produced using crop residue (Zhang et al., 2016) and 34% of research have been conducted to study the effect of biochar on crop productivity followed by 23% of research to study the effect of GHGs emission and 14% for pollutant remediation (Zhang et al., 2016). There are several important functions of biochar in the agro-environment, which are listed in Table 1.1.

Table 1.1

The yield of biochar from biomass hinges on the process of pyrolysis, that is, 12% for fast pyrolysis, 20% for flash pyrolysis, 10% for gasification, and 35% for slow pyrolysis or carbonization (Czekała et al., 2019). Biochar application methods, that is, spot treatment, band application, deep placement, furrow application, broadcasting, etc., depend mostly on the availability of cropping or farming system, and availability of labor and machinery (Das et al., 2020b). In most of small and marginal farms, biochar is applied manually, which may cause health hazards, as the finer biochar particles are generally suspended in the air and may enter the respiratory tract ()(Das et al., 2023). Hence, in most crops, furrow application is recommended against broadcasting (Huggins et al., 2016) and topsoil mixing of biochar along with well-decomposed manure and compost is recommended (González et al., 2015). In most of the research articles, the rate of biochar application is 5–50 t/ha (Huang et al., 2017) but the application rates of 5 and 10 t/ha (0.5 or 1.0 kg/m²) for years have significant advantages on crop productivity and soil health (Kah et al., 2017; Khan et al., 2017). Due to various health issues, the application of biochar of more than 20 t/ha should not be used (Das and Mukherjee, 2020; Ghosh and Kundu, 2018).

1.4 Role of biochar on carbon sequestration and greenhouse gas emission

The importance of biochar in storing carbon and reducing GHG emissions has attracted a lot of attention in recent years. A decrease in atmospheric carbon dioxide levels and possibilities for sustainable soil management is provided by its ability to absorb carbon and affect soil processes. To effectively combat CC and advance sustainable farming, there is a need to comprehend the impacts of biochar in C sequestration and GHGs emission.

1.4.1 Biochar as a carbon sink: mechanisms and potential for long-term carbon sequestration

The unique characteristics and stability of biochar make it an effective option for the long-term storage of carbon in soil and help in lowering atmospheric carbon dioxide (CO2) levels. The mechanisms behind the carbon sequestration capacity of biochar are complex and involve numerous major activities. One of these strategies is resistance to microbial destruction. Due to its high carbon concentration and durability, biochar is resistant to microbial degradation and remains in the soil for a longer period (Grau-Andrés et al., 2021). The resilience allows biochar to operate as a permanent carbon sink, effectively sequestering carbon from the atmosphere for generations or perhaps millennia. Additionally, biochar encourages the production of stable carbon storage in the soil, such as persistent organic matter. This mechanism renders carbon less vulnerable to microbial breakdown and leaching, hence promoting long-term carbon sequestration and increasing soil fertility and resilience (Mukherjee et al., 2014). In addition, soil factors such as pH, texture, and organic matter concentration can influence biochar–soil interactions and eventually affect carbon sequestration capability.

1.4.2 Assessing the environmental benefits and sustainability of biochar as a carbon sequestration strategy

Several elements need to be considered when evaluating the environmental benefits and sustainability of biochar as a carbon sequestration approach. A major issue is the carbon balance involved with biochar production and utilization. To quantify this, a life cycle analysis can be done to determine the net carbon emissions related to biochar synthesis and compared them to the soil carbon sequestration capacity.

Furthermore, the viability of biochar as a carbon sequestration approach depends on its long-term stability and permanence in soil (Laird et al., 2010). Biochar stability is affected by factors such as raw material qualities, pyrolysis conditions, and soil properties. Long-term field studies are necessary to establish the sustainable viability of biochar and its carbon sequestration capability (Kammann et al., 2011).

Analysis of biochar’s ability to lower emissions of GHGs and enhance air quality is also crucial. It has been shown that biochar amendments reduce soil emissions of GHGs such as methane, carbon dioxide, and nitrous oxide. Additionally, enhanced air quality may result from biochar’s capacity to absorb pollutants and decrease their availability in the environment (Zheng et al., 2020).

1.5 Biochar for soil amendment

1.5.1 Biochar as an amendment in soils with physical constraints

Ideal soil health facilitates preserving biodiversity, increasing plant yield and animal productivity, improving water and air quality, and supporting human beings (Nannipieri et al., 2003). Terrestrial plants prefer healthy soil for their optimum growth. Several management techniques have been developed and proposed for enhancing problematic soils, of which biochar, a thermochemical conversion product of biomass, has been found potentially important for amending the soil as it improves soil health (Mandal et al., 2013; Nath et al., 2020).

Biochar application to soil having physical limitations helps in the reduction of bulk density and particle density and improves soil porosity and moisture-holding capacity because biochar has higher porosity, specific surface area, and water-holding capacity because of the existence of various functional groups (Zhang et al., 2012). Soils having higher bulk density are hard in nature restricting proper root development and penetration, and this is the key obstacle for plants growing in soils with physical limitations. When carbonaceous biochar is added to soil, it reduces soil compaction enabling better root penetration and ultimately improving plant growth (Xiang et al., 2017).

1.5.2 Biochar as an amendment in acid soils

Acid soils are characterized by excess concentrations of base cations like aluminum and hydrogen, which affect normal growth of plants. Also due to reduced pH, several essential nutrients are deficient, such as nitrogen, phosphorous, potassium, magnesium, and molybdenum, which hampers plant growth. The beneficial effects are recorded, when acidic soils are amended with biochar, and this alleviation is attributed to several characteristics of biochar, namely, alkalinity of biochar, high pH buffering ability, and effects of various functional groups associated with biochar (Dai et al., 2017). Biochar is the best-suited material as an amendment to neutralize acidity in acid soils. Al³+ present in acid soil is precipitated to less acidic aluminum-containing compounds such as Al(OH)3 and Al(OH)4 with various alkaline oxides, carbonates, and silicates in biochars. Reduction in aluminum concentration, upon addition of biochar, helps in increasing the bioavailability of other essential nutrients such as phosphorus, calcium, and magnesium whose availability was reduced due to the acidic condition of the soil, thus enabling a balanced nutrient supply system in soil providing suitable conditions for better plant growth.

1.5.3 Biochar as an amendment in alkaline soil

Sodium carbonate, which predominates in alkali soils and makes it difficult to clarify or settle the soil, is mostly to blame for the unfavorable physicochemical characteristics of these soils. As most of the biochar is alkaline, they are less helpful in reclaiming alkaline soil. However, biochar of acidic origin is advised for application to alkaline soil. On application of acidic biochar, it acts as a phosphatic fertilizer source and increases the availability of phosphorus (Amin and Eissa, 2017). Also, due to improvement in soil structure and SOM in soil upon treatment of alkaline soil with biochar, there is increased nutrient use efficiency, particularly nitrogen and phosphorus.

1.5.4 Biochar as an amendment in nutrient-deficient soil

The following three reasons ensure better plant growth by adding biochar in nutrient-deficient soil, namely, (1) nutrients provided by biochar, (2) improved nutrient utilization efficiency, and (3) congenial rhizosphere conditions. Inherently, biochars are rich in nutrients such as nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, manganese, copper, zinc, and boron. Depending on the feedstocks and carbonization techniques, the amount of element nutrients present in biochar varies (Gunes et al., 2015; Zafar-ul-Hye et al., 2020a,b, 2021; Zahida et al., 2017; Zahir et al., 2021; Zaman et al., 2021; Zia-ur-Rehman, 2020). In agricultural soil–plant systems, biochar has the potential to enhance N recycling. Adding biochar to agricultural soils decreases N2O emissions, lowers nitrogen leaching, enhances soil nitrogen availability, boosts crop yield, and encourages soil microbial activity. Through its multiple functional groups, namely, carboxylic, hydroxyl, lactone, chromene, and ketone groups, biochar strongly adsorbs different nutrient ions, including ammonium, nitrate, phosphate, and potassium. It also improves soil phosphorus availability by minimizing soil leaching. The application of biochar along with organic or inorganic fertilizers improves nutrient use efficiency (Maru et al., 2015). The improvements in soil CEC and organic matter resulting from the addition of biochar are responsible for nutrient absorption and decreased nutrient leaching, which ultimately increase nutrient utilization efficiency (Fig. 1.1).

Figure 1.1 Mechanisms explaining improved nutrient use efficiency upon the addition of biochar.

1.5.5 Biochar as an amendment in salt-affected soil

Application of biochar to salt-affected soils, that is, saline and alkaline soil, minimizes burdens and enhances plant development (Dahlawi et al., 2018; Tariq et al., 2018; Unsar et al., 2020; Wahid et al., 2020; Wajid et al., 2017; Wiqar et al., 2022; Wu et al., 2019, 2020; Yang et al., 2017a,b, 2022). The improvement in growth is caused by the proclamation of essential plant nutrients such as potassium, calcium, magnesium, manganese, copper, and zinc into salinity-stressed soils to counteract the negative effects of salts. The amendment of biochar with higher potassium contents will lessen sodium uptake by plants and reduce its negative impacts on plants since sodium can partially substitute potassium in plants. Biochar amendment to saline soil increased potassium content in the xylem and decreased tissue sodium and NIK ratio, thus improving potato growth and yield (Akhtar et al., 2015).

1.5.6 Biochar as an amendment in metal-contaminated soil

Biochar is best suited for amendment in heavy metal-contaminated soil. Properties of biochar that are responsible for the remediation of heavy metals in soil are higher specific surface area and CEC, higher pH and abundance of functional groups. Due to the enhancement of surface functional groups in biochar, CEC increases, which is crucial for the reclamation of soils polluted with heavy metals (Mosa et al., 2016; Fakhre et al., 2021; Farah et al., 2020; Farhana et al., 2020; Farhat et al., 2020; Farhat et al., 2022; Fazli et al., 2020). Thereby, biochar by virtue of charged surface functional groups and higher specific surface area combines with toxic metals by adsorption and complexation (Kamran et al., 2017; Khadim et al., 2021a,b; Khan et al., 2021; Khatun et al., 2021). Since the pH value of biochar is mostly alkaline and often rises with pyrolysis temperature, it has the potential to enhance soil pH and CEC values and decreases soil acidity and the bioavailability of several toxic metals (Fig. 1.2).

Figure 1.2 Mechanism of metal sorption to biochar.

1.6 Impacts of biochar on soil physicochemical and biological properties

1.6.1 Physical properties

Among various physical properties of soil, bulk density is an important characteristic and is related to the bonding of the soil particles. Low soil bulk density results in improving the soil structure, making it easier for nutrients to be released and retained, and significantly lessening soil compaction. The amendment of soil with biochar can considerably lower bulk density and boost the overall porous nature of the soil. With a density of 0.05–0.57 kg/m³, biochar is porous and has a lower density than mineral soil. After the addition of biochar, there is stimulation in soil microbial activity, soil agglomeration, and fungal growth influencing soil bulk density (Steiner et al., 2007; Mahar et al., 2020; Mahmood et al., 2021; Manzer et al., 2021; Md Jakir and Allah, 2020; Md Enamul et al., 2020; Mehmood et al., 2022; Mohammad et al., 2020a,b; Mubeen et al., 2020; Muhammad et al., 2019, 2020, 2021, 2022; Muzammal et al., 2021). Biochar by nature is loose and porous with a large surface area (Gul et al., 2015). An enhancement in surface area increases the activities of microbes and facilitates the root growth of plants in soil pores. Soil water content is a prime concern in determining good soil physical properties, and its presence depends on soil texture and rainfall (Fu et al., 2019). Soil hydraulic properties are important to understand the movement of soil moisture as well as nutrients (Carrick et al., 2011; Abrol et al., 2016; Cheng et al., 2006). Biochar is basically black particulate in color and the addition of biochar adds dark color and influences the soil’s surface reflectance, soil temperature, and the amount of heat that is stored in the soil (Fahad et al., 2016a,b,c,d, 2017, 2018a,b, 2019a,b, 2020, 2021a,b,c,d,e,f, 2023).

1.6.2 Soil chemical properties

Biochar application to the soil enhances the SOM content (Zygourakis, 2017). To create SOM, biochar encourages the polymerization of tiny organic molecules by surface catalytic activity and soil macropores can absorb these molecules. The CEC is used to calculate the soil’s capacity for absorption, retention, and exchange of cations. The soil CEC content may rise with an increase in cation exchange sites (Liang et al., 2006). The numerous functional groups (–OH, –COOH) produced by the oxidation of the acidic aromatic carbon on the surface of biochar increase soil CEC and improve soil cation adsorption capacity (Atkinson et al., 2010). According to studies, adding biochar to the soil increases the soil’s overall CEC by 20%–40% compared to the control (Hossain et al., 2010). Biochar is alkaline in nature; hence, it is beneficial for acidic soil. Increased base saturation and soil pH regulation are also possible with biochar. After adding biochar to soils, it can interact with the ions such as H+ and Al³+ to lower their concentration. The application of biochar to an acid soil having a pH of 4.59 increased its pH to 4.86 (Nielsen et al., 2018; Saud et al., 2017, 2020, 2022a,b,c; Senol, 2020; Shafi et al., 2013, 2020; Subhan et al., 2020).

1.6.3 Biological properties

Soil microbial activity is influenced directly or indirectly due to the altered soil physicochemical properties upon the addition of biochar (Fig. 1.3). Biochar is best suited as a habitat for various soil microorganisms, as it supplies place as well as nutrients for microbial growth (Knicker, 2007). The presence of partially soluble carbon sources and N found on the surface of biochar are favorable to microbial activity (Hamer et al., 2004; Fahad and Bano, 2012; Fahad et al., 2013, 2014a,b, 2015a,b). The pores of biochar, on the other hand, are highly variable; their enormous specific surface area and pore structure allow them to store water and nutrients (Palansooriya et al., 2019). The activity and quantity of soil enzymes also increased with the addition of biochar. Turner et al. (2002) suggested a positive correlation between enzyme activity (glucomannan) and the physical and chemical characteristics of the soil, particularly the total SOC (Fig. 1.3).

Figure 1.3 Mechanisms explaining increment in soil microbial population upon biochar addition in soil.

1.7 An insight into the use of biochar versus fantasy

Challenges in achieving food security in this 21st century are worsening due to CC caused by different anthropogenic activities, that is, deforestation and industrialization, posing a serious threat to the sustainability of agro-ecosystem. Biochar is an innovative tool which can offset GHGs and sequester carbon dioxide from the atmosphere into terrestrial carbon pools (Feng et al., 2012; Niaz et al., 2022; Noor et al., 2020; Qamar-uz et al., 2017; Qin et al., 2022). The interest is researching biochar, so-called Amazonian dark earth (Arroyo-Kalin et al., 2009) evolved when the positive effects of biochar-amended Amazonian soils were reported with significant enhancement in yield and improvement in soil quality (Lehmann et al., 2007). It is globally found in different soil due to natural events like forest fires or grassland fires (Krull et al., 2008) which is thermochemical pyrolysis of plant biomass, is a stable form of C which can persist in soil for hundreds of years (Mathews, 2008; Rajesh et al., 2022; Rashid et al., 2020; Rehana et al., 2021; Rehman et al., 2020).

Along with its use in agriculture and CC mitigation, biochar has wider use in various other sectors, that is, wastewater treatment (Lima et al., 2008), cooking (Lehmann, 2009; Lima et al., 2008), increasing building strength on addition with cement (Zeidabadi et al., 2018), feedstock for gasifier (Fryda and Visser, 2015), and so on. The use of biochar in various sectors depends on the economy of its production, which depends on the biomass type and availability along with the process involved in biochar production (Galinato et al., 2011). Biochar has significant positive impacts on the environment, soil, and plants, for which there is growing academic interest of researchers on biochar (Fig. 1.4).

Figure 1.4 Multifaceted impacts of biochar in the present context of climate change.

Moreover, the availability of crop residues and their diversion from other uses, that is, cattle feed, composting, and thatching, and other industrial uses to biochar preparation, and use in agriculture put a strong question on feasibility, scalability, and sustainability of its use (Leach et al., 2010; Sadam et al., 2020; Safi et al., 2021; Sahrish et al., 2022; Sajid et al., 2020; Sajjad et al., 2019, 2021a,b; Saleem et al., 2020a,b,c; Saman et al., 2020; Sana et al., 2022; Saud et al., 2013, 2014, 2016). Further, due to smaller particle size, it can be suspended in the air and has potential negative impacts on human health, which may restrict its long-term uses (Das and Mukherjee, 2020).

1.8 Conclusions

The information in the chapter revealed that to meet the food security of the increasing population, agricultural lands are polluted due to the intensification of agricultural practices to increase crop yield per unit of land. The chapter also highlighted that as a result of crop intensification, soil quality is decreasing through decreasing SOM, increasing erosion, acidification, contamination by heavy metals, salinization, and also excessive use of inorganic amendments leading to the release of various GHGs. Biochar may be used to improve the physicochemical properties of soils as one of the potential cost-effective and environmentally friendly soil organic amendments in the intensive agricultural system under the changing climate.

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