The different effects of applying fresh, composted or charred manure on soil N2O emissions

• After soil amendment, fresh or composted manure emitted more N2O than charred manure.
• The immature compost did not reduce N2O emissions compared with fresh manure.
• The distribution of amendments in soil greatly affected N2O and CO2 emissions.
• The interactions between biochar and other amendments were investigated.

New manure management strategies and technologies are currently being developed in order to reduce manure volume and odorous emissions, utilise energy potential and produce improved manure-derived fertilisers. This has accentuated the need to determine their effects on greenhouse gas emissions after soil application. A laboratory study was conducted over a period of 100 days to investigate the N2O emissions from arable soil amended with different manure-derived fertilisers: fresh, composted and charred solid fraction of pig manure. The importance of several factors (fertiliser type, soil water potential, homogeneous or heterogeneous distribution of amendments in soil) was evaluated in this study. The mitigation potential of the combined application of charred manure with other amendments was also investigated. The application of fresh or composted manure solids was observed to have much higher N2O emissions than that of charred manure solids, which contained low available C and N contents. Contrary to expectations, the immature compost with a high content of dissolved organic carbon did not have lower N2O emissions than fresh manure solids. The homogeneous distribution of compost led to higher N2O and CO2 emissions than heterogeneous distribution. However, the effect of different distribution modes was not significant in treatments with charred manure, since N turnover in the immature compost was much more active than that in the charred manure. By combining charred manure with composted manure, N2O emissions were significantly reduced by 41% at pF 2.0, but the mitigation effect of charred manure was not observed at lower soil water potentials.