Biochar is material produced via pyrolysis of biomass feedstocks. It is a mixture of char and bash, but it is mainly (70 – 95%) carbon (C) (Luostarinen et al. 2010). Charring has a long history, and in many cultures, primitive kilns are still used for making char for fuel.Relatively small volumes of char are being produced in Finland for barbecuing. Potential for production of significant amounts of biochar exist, as pyrolysis based technologies are being developed for energy industry and for production of wide variety of chemicals from forest feedstocks. Internationally, biochar research in recent years has been intensified especially because of the potential biochar provides in carbon sequestration. According to Lehman et al. (2006) biochar as soil conditioner provides an opportunity to annually sequester over 10 % of the carbon emitted due to land use change over the industrial era. This potential is significantly higher than in strategies based on increasing organic carbon in soils, which is estimated to be 0.4 – 1.2 Gt per year (Lal 2004). Cycling of organic carbon from soils to atmosphere is fast in comparison to cycling of biochar, which decomposes only very slowly. The retention times has been estimated to at least hundreds, but more likely thousands of years (Lehmann 2007). Hence, biochar technology provides an opportunity to turn the agri-food sector even to an carbon negative industry. The three main criteria in assessing feasibility of biochar technology are effects on crop productivity and safety, economy, and environment.
More specifi cally, one study estimated that the production of biochar was from 2 to 5 times more likely to reduce greenhouse gas emissions than if the biomass was used just for the production of energy alone (Gaunt and Lehman, 2008). Variation in the pH, ash content, surface area, and other characteristics of biochar is the basis for the concept of “designer biochar” (Novak et al., 2009b), where the characteristics of a biochar are matched to the specific needs of a soil and/or soil management system. The volatile compounds present in certain biochar materials may also represent a fire hazard, but the amount of such compounds found in biochar can be managed by managing the pyrolysis temperature and heating rate (Antal and Gronli, 2003). Different biochar formulations will be best suited to different application methods, and very fine biochar may be desirable in certain cases, for example when applying as a slurry, by itself or mixed with manure (Blackwell et al., 2009). In the published literature, several studies have reported positive effects of biochar application on crop yields with rates of 5-50 tonnes of biochar per hectare, with appropriate nutrient management. This is a large range, but often when several rates are used, the plots with the higher biochar application rate show better results (Chan et al., 2007, 2008; Major et al., 2010b). Instances of decreasing yield due to a high biochar application rate were reported when the equivalent of 165 t of biochar/ha was added to a poor soil in a pot experiment (Rondon et al., 2007). Due to its recalcitrance to decomposition in soil, single applications of biochar can provide beneficial effects over several growing seasons in the field (Steiner et al., 2007; Major et al., 2010b). Adding biochar to sewage sludge or poultry manure during composting has been shown to reduce N losses (Dias et al., 2009; Hua et al., 2009) and the mobility of some heavy metals was also reduced in sewage sludge compost with biochar (Hua et al., 2009). biochar could be applied with individual plants while transplanting in the field, or mixed with topsoil and other amendments while preparing raised beds. Biochar should ideally be applied to an area of soil that tree roots will eventually utilize to take up nutrients, i.e. the “drip line”. The drip line refers to the area you would get, once the tree has reached its mature size, if you drew a circle on the soil corresponding to the size of the tree’s crown. Bio-char is also able to serve as a habitat for extraradical fungal hyphae that sporulate in their micropores due to lower competition from saprophytes, and it can therefore act as an inoculum for arbuscular mycorrhizal fungi (Saito and Marumoto, 2002). Rhizobia spp. living in symbiosis with many legume species are able to reduce atmospheric N2 to organic nitrogen through a series of enzymatic reactions (Giller, 2001). Analyses of conversions of woody biomass to bio-char have shown an average recovery of 54% of the initial carbon in the bio-char (Lehmann et al., 2002). Depending on the temperatures reached during combustion and the species identity of the source material, a biochar’s chemical and physical properties may vary (Keech et al. 2005; Gundale and DeLuca 2006). Biochar addition can result in elevated quantities of bio-available nutrients such as N, P and metal ions, in the affected soils (Tryon 1948; Lehmann et al. 2003; Gundale and DeLuca 2006; DeLuca et al. 2006), but has also been shown to lead to decreases particularly of N availability (Lehmann et al. 2003). Biochar combined with NP fertilizers increased yield significantly compared to plots that received fertilizer or lime alone; suggesting that biochar improved fertilizer use efficiency(Anteneh et al., 2013). Soil management by biochar increase nutrient availability, pH,CEC, crop yields and decreases risk of crop failure as well as opens new possibilities for cropping of high value crops (Edmunds, 2012; Major et al., 2010; Lehman and Ronden, 2006). Lehmann and Rondon (2006) reviewed that an increase in availability of phosphorus after application of biochar could be due to the direct nutrient addition by the biochar and changes in soil microbial dynamics. Biochar is highly porous, contains variable charge, and hence improves surface sorption capacity when added to the soil (Glaser et al., 2002).
The agricultural use of biochar have been growing and attracting more research interest globally due to its potential benefits to crop production, soil fertility and carbon sequestration. Biochar can be prepared from the various organic materials such as crop residues, twigs, forest litters animal residues and other agricultural waste materials.