Pyrolysis temperature influences the characteristics of rice straw and husk biochar and sorption/desorption behaviour of their biourea composite.

Biochar obtained by biomass pyrolysis has several energies, environmental, and agricultural applications. In the present study, influence of pyrolysis temperatures (300 °C, 450 °C and 600 °C) on characteristics of rice residue biochar and sorption/desorption pattern of biourea was investigated. Biochar yield was reduced with the increasing temperature accompanied with increasing carbon content, pH, and electrical conductivity. Elemental O:C and H:C ratios of biochar decreases with temperature. Half-life was predicted between 500 and 750 years varying positively with pyrolysis temperature. Urea sorption/ desorption studies revealed ˃90% sorption in both rice straw and husk biochar with highest urea adsorption at 450 °C, while desorption was more sustained in rice straw biourea. Microporosity, cation exchange capacity and functional groups primarily carboxyl and keto group, played key role in sorption/desorption pattern of biourea with slow release kinetics. Rice residue based biourea composites have potential to raise the crop yields and nitrogen use efficiency.