The effect of biochar feedstock, pyrolysis temperature, and application rate on the reduction of ammonia volatilisation from biochar-amended soil.

Ammonia (NH3) volatilisation is one of the most important causes of nitrogen (N) loss in soil-plant systems worldwide. Carbon-based amendments such as biochar have been shown to mitigate NH3 volatilisation in agricultural soils to various degrees. In this study, we investigated the influence of biochar feedstocks (poultry manure, green waste compost, and wheat straw), pyrolysis temperatures (250, 350, 450, 500 and 700°C) and application rates (1 and 2%), on NH3 volatilisation from a calcareous soil. The 15 biochars were chemically characterized, and a laboratory incubation study was conducted to assess NH3 volatilisation from the soil over a period of four weeks. Furthermore, changes to the bacterial and fungal communities were assessed via sequencing of phylogenetic marker genes. The study showed that biochar feedstock sources, pyrolysis temperature, and application rates all affected NH3 volatilisation. Overall, low pyrolysis temperature biochars and higher biochar application rates achieved greater reductions in NH3 volatilisation. A feedstock related effect was also observed, with poultry manure biochar reducing NH3 volatilisation by an average of 53% in comparison to 38% and 35% reductions for biochar from green waste compost and wheat straw respectively. Results indicate that the biogeochemistry underlying biochar-mediated reduction in NH3 volatilisation is complex and caused by changes in soil pH, NH3 sorption and microbial community composition (especially ammonia oxidising guilds).