An in-situ Technique for Producing Low-Cost Agricultural Biochar

Application of biochar to agricultural soils is effective to sequester atmospheric carbon and improve soil quality, but current pyrolysis and transportation costs are high, making biochar too costly to be used at the field scale. This study developed a new in-situ technique, burning and soil covering (B-SC), which can be used by farmers for production of biochar with crop residue. In this study, the air-dried feedstocks, elephant grass and corn residue, were burnt in situ for biochar production in the field. After approximately 90% of the leaves were combusted, the burning process was dramatically slowed down by covering the feedstock with soil. The biochar yield averaged 18.0 ± 1.3 (n = 15) and 13.7 ± 1.3 (n = 10) kg per 100 kg air-dried feedstock for the elephant grass and corn residue, respectively. The biochar properties were suitable for soil improvement. The inputs for biochar production of the B-SC process only included low labor force, open field, feedstock (e.g., grass and crop residue), and simple tools. The operation time for processing 10 kg of the corn residue by an individual farmer was 24.4 ± 4.1 min (n = 10). As compared with the conventional field burning process, the B-SC process drastically shortened the time for biomass burning and generated a significantly lower emission of smoke and thermal energy. This simple technique can be particularly practical and effective for farmers to improve the soils of poor quality in China.