Nitrous oxide is the third important greenhouse gas, has a life span of 114 years in the atmosphere and has 296 times more global warming potential than CO2. About 30-45% N2O emission was proved to be from anthropogenic sources in the world. By 2030 , it is estimated that 5.72 % of anthropogenic N2O-N emission is from the aquaculture industry if it continues to grow at the present annual growth rate of 7.10 %. The production of N2O in aquaponics is an unavoidable concern when aquaponics is developed as a future production system. Aquaponics has less N2O conversion ratio (1.3%) than Aquaculture (1.5% -1.9%).
The amount of dry crop residue generated by nine major crops (Rice ,Wheat, Maize, Jute, Cotton, Groundnut, Sugarcane, Rapeseed & Mustard, Millets) was 620.4 Mt. These residues are not utilised and become a source of greenhouse gases. It can be converted into a useful product through pyrolysis, the pyrolysed product called Biochar. Biochar is the by-product of biomass pyrolysis in an oxygen-depleted atmosphere. It contains a porous carbonaceous structure and an array of functional groups. Biochar can be added to the grow bed when added Biochar mitigates N2O. Biochar has aromatic compounds, which is very stable, also has redox activity and mainly function as a reducing agent. Biochar mitigates the nitrogen compounds by adsorption of NH3 or organic-N onto biochar, cation or anion exchange reactions and enhanced immobilisation of N as a consequence of labile C addition in the biochar.
Another primary challenge in Aquaponics is disease control. Biochar is reported to effective against pythium sp which is common soil pathogen in the Aquaponics system. Biochar can be effective against both soilborne pathogens (e.g. Fusarium spp., Phytophthora spp., Rhizoctonia solani) and airborne (e.g. Botrytis cinerea, different species of powdery mildew). It is also reported that five different mechanisms to explain biochar disease suppression : (i) modifies the nutrient availability and biotic condtions; (ii) induction of systemic resistance in host plants; (iii) increases the activities of beneficial microbes, including mycorrhizal fungi; (iv) fungicidal in nature (v) adsorption of toxic chemical that promote the attack of pathogens