Biochar use for climate-change mitigation in rice cropping systems

This study estimated the climate change effects of alternative rice production systems in North Vietnam with different residue management options, using Life Cycle Assessment (LCA). The traditional practice of open burning of residues (System A) was compared with the alternative of converting residues to biochar, which was returned to the same land area from which the residues were obtained (System B). Pyrolytic cook-stoves and drum ovens were assumed to be used by households to produce biochar, and the cook-stoves produced heat energy for cooking. The annual rate of biochar applied was determined by the amount of biochar produced from the straw and husk available. We assumed that agronomic effects of biochar increased with each annual biochar application until reaching maximum benefits at 18 Mg ha⁻¹, which takes eight years to be produced in pyrolytic cook-stoves and drum ovens. The largest contributor to the carbon footprint of rice at the mill gate, was CH₄ emissions from soil, in both systems. Biochar addition reduced the carbon footprint of spring rice and summer rice by 26% and 14% respectively, compared with System A, in the first year of application. These values substantially increased to 49% and 38% after eight years of biochar addition. The climate effect of System B was most sensitive to the assumed suppression of soil CH₄ emissions due to biochar application.