*1.4.4 Role of biochar in sustainable plant disease management*

The ever increasing desire to increase agricultural efficiency in terms of producing maximum crop yields and produce is only achievable if pest and disease agents affecting crop productions are effectively monitored. Interventions such as cultural, biological, chemical and regulatory measures are the main approaches to plant disease management. The chemical method, since its adoption over a century ago, had assumed a position of significance and preferred over the existing cultural method as a result of its effectiveness in the management of diseases and pests. The availability, stability and quick-action, relatively low cost of the chemicals and ease with which they can be used, limits the harm done to crops. With the apprehension of the havoc, however, caused by continuous and persistent use of chemicals either by misuse or abuse, with the consequent degradation of ecological community of most of the farm sites based on their effects on both the target and non-target organisms, has led to the destruction of beneficial organisms and the natural predator in the eco-system. The normal functioning of the ecosystem is obstructed if the organisms develop resistance to the chemicals used, thus resulting in pests evolution. Consequently, agricultural workers suffer occupational exposure to pesticides whilst the general population is exposed to pesticides pollution principally through the food chain and drinking water contaminated with pesticide residues which are carcinogenic [98].

### **1.5 The role of biochar in mitigating climate change**

Biochar can satisfy the following targets: achieving food security by enhancing crop productivity, promoting soil health and quality by improving soil properties, avoiding land degradation, reduction of greenhouse gas emissions minimises climate change, and adsorbing hazardous elements onto its surface. The conversion of *terra preta* soil into highly fertile soil due to biochar application is excellent evidence of biochar's role in soil sustainability and the environment. Many greenhouse gases are from the agricultural sector primarily due to many crop residues burning. A considerable amount of CO2 is released from the fields, hampering the quality of the environment. The use of biochar has been well-thought-out, a novel technique to make a slow continuing elimination of CO2 from the terrestrial atmosphere due to its complex aromatic structure and recalcitrant nature. The conversion of residue into biochar is considered a better alternative against burning. About 50% C retains in the soil in converting biomass C to biochar C than traditional conservation agriculture and microbial degradation, providing a more stable *Sustainable Use of Biochar in Environmental Management DOI: http://dx.doi.org/10.5772/intechopen.96510*

soil C sink than burning or direct biomass application [9]. Thus, applying biochar to soils can play an essential role in C sequestration to mitigate climate change as its residence time is up to millennial time scales [99]. On a global ranking of removing C from the atmosphere, biochar-bioenergy can play a significant role in inhibiting erratic climate change. It helps to capture and store C from the atmosphere at lower prices, where biochar addition significantly enhances the crop yield. About 62–66% of CO2 emissions could sequester within biochar [100]. Thus, biochar can be an advantageous element to sequester more CO2 from the soil's atmosphere to mitigate climate change. Besides CO2, the emission of other greenhouse gases such as methane (CH4), nitrous oxide (N2O) has become a significant threat to the environment. Biochar application to the soil decreases the emission of CH4 by suppressing the oxidation of ambient CH4 depending upon soil type, the properties of biochar, and environmental conditions. On the other hand, the impact of biochar on the nitrogen transformation process is still unknown. Compared with other fresh organic materials, biochar application helps reduce N2O emission and NH4 + leaching from the soil. Biochar reduces N2O emission at reduced paddy fields due to the oxidative reactions on the biochar surfaces with ageing [86]. The biochar addition at the rate 20 and 40 Mg ha−1 reduced the total release of N2O by 10.7% to 41.8%, respectively [101]. Furthermore, soil N2O fluxes have also decreased to 79% in biochar treated soil [102].

#### **1.6 How safe is the use of biochar on the environment?**

The process of biochar production transforms the easily oxidised carbon fractions present in organic residues into more stable forms [5] that can persist in soils for years [103]. The incorporation of biochar reduces the emissions of greenhouses gases [104] and can be considered as a climate change mitigation strategy [105]. On the other side of the coin, required quantities of this conditioner to improve soil productivity might be less comparable with compost or other organic amendments on the long run. Consequently, biochar also known as "the black diamond" is offered as a promising soil amendment of high economic and environmental value [106]. However, several environmental traits should be taken into consideration whilst using this amendment. The primary one to consider is the production process. During the pyrolysis process of biochar, significant emissions of CO2 occur and this probably may raise the levels of greenhouse gases in atmosphere [107]. The second important issue has to do with the degradation of biochar in the soil. Under warm climatic conditions, biochar degradation is reported to be relatively high [6] and therefore, further emissions of greenhouse gases might take place from biochar-amended soils. The third relates to ethylene production, which is a byproduct of the pyrolysis process of biochar [108]. Ethylene is increased considerably in biochar-amended soils to subdue several soil microbial processes [82]. Soil biota not only affects the physical and chemical properties of soil but also improves plant health [80]. Several researches have established the positive influences of amending soils with biochar on increasing crop productivity. Soils Amended with biochar have been proven to significantly improve macro- and micro-nutrients availability [6], even though many biochar additives have an alkaline nature [76]. Furthermore, amending soils with biochar reduces nitrate (NO3) loss through leaching as well as the gaseous loss through release of nitrous oxide [92], which can positively boost plant growth [93].

However, the effects of amending soils with biochar are not always the similar and depend mainly on the features of the biochar used such as grain size and pyrolysis temperature. Fine biochar decreases soil hydraulic conductivity (EC), whilst the coarse biochar (particles were coarser than sand) did not affect the

hydraulic conductivity of soils [95]. In addition, the pyrolysis temperature for the production of the biochar has a significant effect on ash content, pH, EC, and basic functional groups as well as carbon stability, which increases in biochar with increasing pyrolysis temperature [109]. Another positive influence of biochar as a soil conditioner is related to its ability to mitigate salinisation of arable lands [110]. It is noted that biochar plays positive significant influence on regulating the contaminants present in water and soils [111]. Conversely, many contaminants such as atrazine and acetochlor that are sorbed on biochar [107] may also originate from biochar [112] and this may reduce its efficacy [98]. Although biochar plays important positive roles on environmental sustainability, there is a stream of knowledge regarding the recommended application rates to soils to evade its negative potential effects on the environment.
