Biorefineries use thermochemical processes (pyrolysis and carbonization) to convert biomass into biofuels and other bio-energy products [24; 25]. Major thermochemical technologies for biochar production include slow and fast pyrolysis, gasification, torrefraction and hydrothermal carbonization [24]. Slow pyrolysis of biomass can be used to produce biochar, whose properties depend on feedstock properties as well as the reaction temperature and duration [22; 23; 24; 25; 26]. The chemical and physical properties of biochar (and thus its value) can be fine-tuned by modification of these reaction conditions [25]. The utility of biochar has been demonstrated in reducing the need for agrochemicals, increases in productivity, long-term improvement in soil conditions and reduction in greenhouse gas emissions through soil sequestration as well as indirectly through increasing the efficiency of fertilizer use [22; 23; 24; 25; 26]. Asia's agricultural sector generates large volumes of agricultural residues every year [26]. Crop residues contribute to 80% of the global production of biomass dry matter (8201 Tg/year) of which 3137 Tg/year are potentially available after pyrolysis [27]. The use of agricultural residues as a feedstock for biochar production is therefore of interest for use as a soil amendment, with potentially significant environmental, production and economic benefits. Thailand's economy relies on agricultural products. The country's agricultural sector generates a large volume of crop residues including paddy husks, sawdust, corncobs, cassava stems and cassava rhizomes. Production data collected by the Department of Agricultural Extension between 2006-2007 indicated that Thailand produced 4.40 million tons of corn and 17.6 million tons of cassava of which 0.84 million tons were corncobs, 2.11 million tons were cassava stems and 1.76 million tons were cassava rhizomes [28]. Normally, agricultural wastes are simply left in the field to decompose or burned. Burning crop residues adds to GHG emissions, resulting in severe impacts on air quality, biodiversity and human health. Although burning is convenient, quick and cost-effective, and allows fast preparation of the field for the next rotation, some farmers nevertheless choose to incorporate crop residues into the soil to maintain long-term soil fertility. Soil incorporation of biochar from crop residues offers an attractive alternative to open field burning. Instead of burning, farmers can deal with their large volumes of crop residues by converting it into biochar using slow pyrolysis. The biomass is heated at 500-600 \({}^{\circ}\)C in a reduced oxygen or fully anoxic atmosphere [29; 30]. Compared with other methods, pyrolysis has proved effective in converting residues into biochar as a highly stable solid [31]. Moreover, several studies confirm that biochar is effective as a soil ameliorant and can even increase crop yields [32; 33; 34]. Biochar is highly stable, comprising more than 65% carbon. Chemical composition is highly dependent on feedstock and pyrolysis conditions [35; 36; 37; 38]. Biomass subjected to pyrolysis is converted to biochar with high fixed carbon content and high stability. Biochar's stability in soil is crucial to its long-term environmental benefits. Because of its long-term stability, biochar can be used for carbon sequestration, mitigating climate change by locking carbon in the soil. The stability of biochar ensures longevity of expected benefits for soil, crops, water resources and climate change mitigation [39]. Biochar also regulates and increases availability of cationic plant nutrients such as P, K, Na, and Mg [27]. In addition to its direct agronomic benefits (enhanced fertilizer use efficiency, higher yields and improvement in soil fertility), biochar delivers three primary environmental benefits: sequestrating carbon in soils, reducing greenhouse gas emissions [39; 40] and reducing pollution via runoff of fertilizers and pesticides into waterways and groundwater.