Influence of temperature and duration of pyrolysis on the property heterogeneity of rice straw biochar and optimization of pyrolysis conditions for its application in soils

The study reports an investigation into the effects of temperature and duration of the pyrolysis on the yield and properties of the rice straw biochar and their optimization for application in soil based on the results of seed germination test. As a continuation, the effects of rice straw biochar on the growth of mung beans germinated using extracts of biochar, which were maintained at different pHs was studied. Biochar solvent extraction was done by mixing a predetermined dose of rice straw biochar to solutions initially maintained at five different pH conditions (4, 6, 7, 8, and 10). The biochar extracts were also characterized for their pH, electrical conductivity, and nutrient values and correlated with the germinated seed lengths. Further, this study based on the results of seed germination optimized the rice straw biochar production conditions with such properties to promote maximum seedling growth. Results showed that the yield of biochar decreased from 45.04% to 33.45% as temperature raised from 400 degrees C to 700 degrees C. The properties of biochar are primarily affected by the temperature as compared to the heating duration of the pyrolysis. The crystallinity index in the rice straw biochar decreased by 15.25% with the increase in the temperature from 400 degrees C to 700 degrees C. Correlation test among seed lengths and biochar extracts properties showed that the seed growth was directly correlated with the increase in the nutrient values at all pH conditions. Based on the germination test, the optimized conditions for the maximum seedling growth observed as for high nutrients, carbon (35-40%) and moderate nitrogen (3-4%), ash (32-35%), yield (35-40%) and cation exchange capacity (40-45 cmol/kg), carbon-nitrogen ratio (22-25:1), low oxygen-carbon ratio (0.7-0.8), ideal pH (8-9), and low volatiles (44-48%). The optimized pyrolytic temperature and duration to produce rice straw biochar with above-listed properties modelled as 500 -600 degrees C and 80-100 min respectively. (C) 2019 Elsevier Ltd. All rights reserved.