Full greenhouse gas balance of silage maize cultivation following grassland: Are no-tillage practices favourable under highly productive soil conditions?

Abstract Intensification of forage production often leads to conversion of grassland to arable land, with associated high greenhouse gas (GHG) emissions. By implementing seeding with minimal soil disturbance, i.e. no-tillage, reduction of GHG emissions is possible, while crop yields can still be considerable. On a sandy loam in the Eastern Uplands of Schleswig-Holstein, Northern Germany, a two-year field experiment (Apr 2015 - Mar 2017) was set up, with a 10-year-old grassland sward converted to silage maize (Zea mays L.) with i.) conventional tillage by mouldboard ploughing (CT) and ii.) no-tillage (NT) representing the factor management. The factor N-fertilization consisted of two levels: 90 kg N ha−1 (N1) or no fertilization (N0). The annual N2O, CH4 and CO2 emissions were assessed with the closed chamber method. Global warming potential (GWP) expressed in CO2 equivalents (CO2eq) was calculated on an area basis and at product level to compare the different management systems. The N2O emissions were significantly increased after conversion in the first experimental year but showed no effect of the factor management. The annual GWP was on average highest in the CT treatments with 23.9 (N0) and 29.3 t CO2eq ha−1 (N1), while NT reduced GWP by 67 and 46 % for N0 and N1 compared to CT. Biomass removal by harvesting dominated the GWP in all treatments. Yield-related emissions were significantly lower in NT than CT maize, thus indicating higher eco-efficiency of this management system.