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Biochar—An Imperative Amendment for Soil and Environment

Introduction

Continuous cultivation with a rice-wheat cropping system and large scale residue production leads to burning of surplus rice in the open field, which in Umi leads to severe air pollution and greenhouse gases emission from field. The word “biochar” is a combination of ‘bio' and ‘char’. Bio means ‘biomass' and char means ‘ charcoal'. Biochar is a carbon rich stable substrate obtained after pyrolysis (combusted under low or no oxygen conditions) of organic biomass or agricultural residues. During the production process of biocliar. bio-oil and gases are also produced as a byproduct which can be used hi other industries and for other purposes. Biocliar is a form of carbon rich charcoal that is formed by the pyrolysis (thermal decomposition) of organic biomass or agricultural residues (raw materials) which is used as soil conditioner (Xiao et al. 2014). Biochar is also defined as charcoal produced from plant matter and is stored in the soil as a means of removing carbon dioxide from the atmosphere. Biochar is the carbon-rich product obtained when biomass, such as wood, manure, crop residues or leaves, is heated in a closed container with little or no available air. Biocliar is charcoal used as a soil amendment. It is highly heterogeneous in nature and composed of stable and labile components. Major components of biocliar are carbon (C), volatile matter, mineral matter and ash. These occur in different proportions according to biomass used for biochar preparations. Physically, it is dark black in color (Figure 1) and its highly porous structure makes it attractive. In biocliar, most of the carbon is recalcitrant in nature; therefore, it helps in carbon sequestration by locking the carbon present in the plant biomass. From agriculture pomt of view, biochar has major role in soil management, carbon sequestration issues, and immobilization of pollutants (especially heavy metals). Recalcitrant carbon in biochar has multiple benefits ranging from soil improvement to waste management and mitigating climate change. Biochar is mainly used to improve soil nutrient content and to sequester carbon from the environment (Lehmann 2009). It has been estimated that through production of biocliar, almost 12 per cent of the GHG emissions caused by human activities could be reduced (Woolf et al. 2010). Biocliar acts as a carbon sink and it reduces decaying and

Biochar

Figure 1. Biochar.

mineralization of the biological carbon cycle to establish a carbon sink. In recent years, the use of surplus organic matter or biomass (especially rice and wheat) for the production of biocliar has yielded promising results in the reduction of C02 and mitigating climate change. Biochar is used for amendment of acidic soils (low pH soils), it increases basicity of acidic soils and also increase agricultural productivity. Recently, several researches were done in biocliar, their properties and effects on crop yields. Currently, many projects are being earned out on biochar. In this chapter, we will discuss about biocliar, its production, elemental composition, differences in biochar according to feedstocks used, effect of biochar on soil carbon sequestration, reducing heavy metal pollution, mitigation of climate change, etc.

Production

Biochar production is thermo-chemical conversion of biomass under low or no oxygen environment. There are different steps (fast pyrolysis, slow pyrolysis, gasification, and carbonization) involved hi the production of biocliar, which are depicted in Figure 2.

Step by step process for biochar production

Figure 2. Step by step process for biochar production.

3. Effect of temperature and heating rate on biochar production

With increase in temperature, biochar production decreased, primarily due to depolymerisation of compounds like cellulose and hemicellulose as well as combustion of organic materials (Coopennan

2016, Cao and Harris 2010). The decrease in yield with increase in temperature is due to increase in volatilization rate of organic compounds (Muradov et al. 2012). Evolution of moisture occurs at 220°C. The high yield of biocliar at low temperatures indicates that the material has been only partially pyrolysed (Katyal et al. 2003, Yang et al. 2004). The chemical properties of biocliar are also greatly affected by temperature and heating rate. With the increase in the temperature, the pH values of the biocliar also increased (Angin 2013). Similar results were also reported by Pannila and Saroha (2014) and Jindarom et al. (2007). Yuan et al. (2011) suggested that the increases in pH values might be attributed to the separating of alkali salts from organic materials due to increase in pyrolysis temperature. With the increase in the pyrolysis temperature, the carbon content in the biochar increases, while the oxygen and hydrogen content decreases with respect to carbon content (Chen et al. 2011. Chun et al. 2004). Coopennan (2016) suggested that cracking of weak bonds within the biocliar structure might be attributed to loss in hydrogen and oxygen content. Lua et al. (2004) observed that with the increase in temperature, there is a decrease in the Bmnauer-Emmett- Teller (BET) surface area. Lehmann (2007) suggested that the Cation Exchange Capacity (CEC) is directly proportional to temperanire at which the biocliar is produced, that is, CEC increases significantly with the increase in the temperahire.

 
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