Biochar amendment to cattle slurry reduces NH3 emissions during storage without risk of higher NH3 emissions after soil application of the solid fraction

•Biochar reduces NH3 emissions during cattle slurry storage up to 20%•Biochar improves the separation efficiency and the quality of the solid fraction.•Biochar increases C, (organic) N and water-available P in the solid fraction.•S° is only successful for reducing NH3 emissions in combination with biochar.•Biochar results in a short term priming effect on the C mineralization of manure.