Langfristige Effekte einer Grünlanderneuerungsmaßnahme auf den Bodenkohlenstoffgehalt und die N2O-Emissionen

Summary

An increased demand for renewable raw materials for food and energy production has led to an increased intensification of agricultural production in northern Europe. Grassland, as well as arable production, has been affected by this development. Extensive grassland swards are often renovated with the aim of improving herbage yield and quality. The renovation of grassland leads to a reduction of CO2-C-fixation rates and increased soil mineralization processes. As a result levels of carbon losses and nitrous oxide (N2O) emissions increased in the short-term [1, 2]. Few studies have been carried out on the development of soil carbon and nitrous oxide emissions in medium or long-term (>1 year). In order to identify carbon sequestration and N2O-emissions from grassland of different sward ages (2, 5 and 18 years after grassland re-establishment) a two-year field experiment was conducted on a sandy loam (53% sand, 19% silt, 18% clay, 1.8% Corg and 5.9 pH) in 2010/2011 (2011/2012). The experiment was set up in a split-plot design with three replications (n=3) including a control (no fertilizer) and a fertilized treatment (240 kg N ha-1 year-1as cattle slurry). The N2O-emissions were measured using the closed chamber method on a weekly basis [3].The soil carbon content was measured twice a year from soil cores.
Results showed a lower soil carbon content (0-30 cm) in the two year old sward (63.74 t C ha-1) compared to the 5 year old (72.84 t C ha-1) and 18 year old sward (77.16 t C ha-1) (p≤0.05). No significant relationship could be found between the cumulative N2O-emissions per year and sward age. On average the 18 years old fertilized grassland showed the highest N2O-Emission compared to all other treatments in both experimental years (2.56 kg N2O-N ha-1 in 2010/11 and 1.17 kg N2O-N ha-1 in 2011/12).
Grassland renovation leads to a decay of soil carbon. In our experiment this effect was compensated within five years of grassland re-establishment (p≤0.05). On average the N2O-emissions were low in younger swards compared to old grassland (n.s.).