Does soil amended with biochar and hydrochar reduce ammonia emissions following the application of pig slurry?

Combining amendments to the soil made by biochar or hydrochar with nitrogen (N) fertilizer can modify soilN dynamics and availability. Such a response suggests that these amendments would affect ammonia (NH3)emissions from slurry similarly, and potentially reduce volatilization of NH3. This study measured the potentialemissions of NH3following application of pig slurry to the surface of silt-loam and loam soils amended withbiochar and hydrochar (both derived from Miscanthus × giganteus (Greef et Deu)) at a rate of 3% soil dry weight(16 t ha−1soil area, on average) and 60% water-lled pore space (WFPS). The experiment was carried out in adynamic chamber connected to a photo-acoustic trace gas analyser in a controlled climate (20∘C) for 48 hours.Statistically signicant differences (P < 0.05) in total emissions were observed between both treatment and soiltypes. Surprisingly, both amendments increased emissions of NH3compared with the control; cumulative NH3emissions averaged 38.7 and 23.5% of applied total ammonium nitrogen (TAN) for hydrochar and biochar,respectively, whereas it was 18.2% for the control. The larger emissions in hydrochar-amended soil wereattributed to the reduced ability to absorb NH4+associated with greater hydrophobicity and strong pH buffering ofthe slurry. Furthermore, nal soil analyses with deionised water extracts showed signicant differences (P < 0.05)in mineral N concentration between treatments. The smaller ammonium concentrations in biochar-amended soilsuggest that some NH4+-N was immobilized by adsorption on to biochar surfaces. This study observed thatbiochar and hydrochar properties, as well as soil characteristics, play important roles in controlling NH3emissionsfrom surface slurry applications. The results obtained identied circumstances where these amendments evenenhance volatilization, which provides new information on and insight into the extent and limitations of thepotential of biochar and hydrochar for the mitigation of emissions.