Effect of feedstock, pyrolysis temperature and application rate on biochars’ ability to reduce Influence of manure based biochars on ammonia volatilization from soil

Ammonia (NH3) volatilization is one of the most important causes of nitrogen (N) loss in soil-plant systems worldwide. In recent years, carbon-based amendments such as biochar have been shown to mitigate NH3 volatilization in agricultural soils. 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 the NH3 volatilization from a calcareous soil. The 15 biochars were chemically characterised and a laboratory incubation study was conducted to assess NH3 volatilization 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 feedstock sources, pyrolysis temperature, and application rates played a major role in reducing NH3 volatilization. Overall, low-temperature biochars and 2% application rates were more effective to reduce NH3 volatilization than the other treatments. There was also a difference between feedstocks with biochar from poultry manure able to reduce NH3 volatilization by 53% (as average) while biochar from green waste compost and wheat straw reduced volatilisation by a smaller degree (38 and 35% respectively). The reduction in NH3 volatilization appears to be complex with the effect that biochar has on soil pH, sorption of NH3 by the biochar and changes in microbial communities (especially ammonia oxidisers) playing a role.