The potential use of biochar to reduce nitrogen waste from farming systems in India

The aim of this paper is to quantify the impact of incorporating biochar into soils on net nitrogen waste from farming systems in India. It assumes only crop residues that are currently burnt in the fields are used to produce biochar. It accounts for losses of nitrogen occuring during pyrolysis, and the potential savings due to capture of reactive nitrogen from other parts of the farming system and from industry and energy sectors. In 2020, this could have been used to capture up to 67% of the nitrogen lost as nitrogen oxides and ammonia from the energy, industry and farming sectors. This is equivalent to 31% of the nitrogen that was applied as fertilisers and so could be an important tool in efforts to meet the United Nations target to reduce nitrogen waste by 50% by 2030. However, if the rate of nitrogen capture is low, alternative uses for crop residues are developed, or wasted nitrogen is successfully captured by other methods, the benefits of nitrogen capture on biochar could be much lower. Nevertheless, using biochar as a method to deliver wasted nitrogen to crops is likely to sequester more carbon than alternatives because pyrolyzed carbon is highly recalcitrant. It is also likely to be a more reliable method of capturing nitrogen emissions and delivering nitrogen to crops because emissions of ammonia during storage and spreading of compost or bioslurry can be high. Therefore, even if alternative uses of crop residues are favoured by farmers, it is recommended that nitrogen sorption on biochar should be part of the process, whether it is by direct capture of nitrogen from urine and industrial nitrogen oxide emissions, or by mixing of biochar with compost or the ammonium rich bioslurry produced by anaerobic digestion.