Effect of agricultural management system (“cash crop”, “livestock” and “climate optimized”) on nitrous oxide and ammonia emissions

Abstract

The study aimed to measure soil-atmosphere N₂O fluxes and their controlling factors, as well as NH₃ emissions and yields for two soils (silt loam and clay loam) in three management systems over two years under subsequent wheat and maize cultivation. The management systems were characterized as follows: (1) cash crop (C) with mineral fertilizer and conventional tillage; (2) livestock (L) with biogas residue fertilization and its incorporation prior to sowing in maize and reduced tillage; and (3) climate optimized (O) with minimum tillage, 8-year crop rotation, with biogas residue fertilization, in maize without incorporation in clay loam soil or incorporation by strip-tillage prior to seeding in silt loam soil. Stable isotope ratios of N₂O and mineral N were determined to identify N₂O processes. Within the organically fertilized maize treatments, cumulative N₂O fluxes were highest in the O-system treatments of both sites (4.0 to 9.4 kg N ha^− 1 a^− 1), i.e. more than twice as high as in the L-system (1.5 to 3.1 kg N ha^− 1 a^− 1). Below root-strip till fertilizer application did not enhance N₂O fluxes. Fluxes with mineral fertilization of wheat (1.1 to 3.1 kg N ha^− 1 a^− 1) were not different from those with organic fertilization. Isotopic values of emitted N₂O revealed that bacterial denitrification dominated most of the peak flux events, while the N₂O/(N₂ + N₂O) ratio of denitrification was mostly between 0.1 and 0.5. It can be concluded that, contrary to the intention to lower greenhouse gas fluxes by the O-system management, the highest N₂O fluxes occurred in the O-system without biogas digestate incorporation in maize. With respect to NH₃ fluxes, we could confirm that the application of digestate application in growing crops without incorporation or late incorporation in fertilization before sowing induces high fluxes. The beneficial aspects of the O-system including more stable soil structure and resource conservation, are thus potentially counteracted by increased N₂O and NH₃ emissions.