Mitigating nitrogen losses from manured agricultural soils: the impact of manure plasma activation

Application of manure to agricultural soils can improve soil quality and productivity by maintaining its nutrient status and organic matter (OM) content. Resulting nitrogen (N) emissions in the form of ammonia (NH3) and the greenhouse gas nitrous oxide (N2O) may however lead to substantial environmental pressure. Manure plasma activation has been advertised as an innovative technique that lowers nitrogen losses during and after soil application, although the scientific documentation on its effects is still limited. Here, we conducted a mesocosm study to quantify gaseous losses of NH3 and N2O from plasma activated manure (PAM) and non-treated raw manure (RM) applied to soil. In general, plasma activation caused significant changes in manure characteristics (i.e. OM degradation, pH, NO3- concentration) affecting gaseous N emissions. At a dose of 170 kg N/ha, PAM showed substantial reduction of NH3 volatilization compared to RM, whereas N2O emissions increased significantly. Manure plasma activation resulted in a decrease of total atmospheric N losses. Still, the observed increase in N2O flux raises the question of the environmental impact of PAM application. In line with the elevated NO3- concentrations, N2O fluxes from PAM started shortly after application, whereas highest fluxes were observed for RM after 7 days only. Altogether, the results show an important tradeoff between NH3 and N2O emissions from these manure products and indicate that PAM may be better used as topdress fertilizer instead of a replacement for RM to maximize plant NO3- uptake and minimize gaseous N losses.