Volatilisations of ammonia from the soils amended with modified and nitrogen-enriched biochars

Biochar's capacity to abate NH3 emissions from fertilised agricultural soils may be enhanced through both modifications and formulation of slow-release biochar-based N fertilisers but there is a dearth of data in this area. Sulphuric acid (H2SO4), hydrogen peroxide (H2O2) and potassium hydroxide (KOH) were used to modify biochars which are denoted as BSAD, BHPO and BKOH, respectively. Nitrogen (N) enrichment was performed using urea and ammonium nitrate and the enriched biochars are denoted as BUR and BAN, respectively. The biochars were characterised by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The ammonia abatement potentials of both the modified and N-enriched biochars were assessed in the incubation experiments which lasted for 30 days. Urea was used as a control while non-modified biochar (PrBC) was included for comparison. Compared to the control, PrBC, BKOH, BHPO, BSAD, BUR and BAN attenuated gaseous NH3 emissions by 57.62%, 63.06%, 73.23% and 74.85%, 79.93% and 82.88%, respectively. Biochar modifications increased the content of oxygen containing surface groups especially carboxyl and sulphoxide in the case of BSAD as depicted from the instrumental analysis data, which most probably increased the sorption of NH3 and its transformation to nitrates thus, resulting in a higher NH3 abatement capacity than that of PrBC. XPS data indicated that N-enrichment resulted in reactions of N with the surface groups of biochar which slowed its release, concomitantly lowering NH3 volatilisation better than even the modified biochars.