Increased nitrogen fertiliser value of cattle slurry by different slurry pre-treatments

Abstract The nitrogen (N) fertiliser value of cattle slurry is often low, due to a high carbon/nitrogen (C/N) ratio limiting slurry N availability, and high viscosity leading to slow slurry infiltration and increased risk of ammonia emissions. In this study, the effect of treatments reducing the slurry C/N ratio in combination with measures to reduce ammonia emissions after slurry application was tested. Seven field fertilisation experiments were conducted in winter wheat fields and grass leys in southwest Sweden during a three-year period. Slurry types included were untreated cattle slurry (CS), the liquid fraction (LF) from screw-press separation of cattle slurry, and biogas digestate (BD) with cattle slurry as the main substrate. Application strategies included trailing hoses, trailing shoes, and acidified slurry applied with trailing hoses. Trailing shoe application was further studied in two additional experiments in spring oats. In winter wheat and grass ley, the N fertiliser value, expressed as Mineral Fertiliser Equivalents based on the amount of applied ammonium N (MFE NH4N ), was lowest for CS applied with trailing hoses (31%). Slurry separation and anaerobic digestion increased MFE NH4N to 55% and 52%, respectively. Slurry acidification increased MFE NH4N for CS to 52% and for BD to 82%, while the effect for LF was non-significant. In most cases trailing shoe application did not increase MFE NH4N compared with trailing hoses. In conclusion, this study shows that the N fertiliser value of cattle slurry can be increased in several ways, with a combination of anaerobic digestion and slurry acidification resulting in the largest increase.