Field assessment of the balance between greenhouse gases and ammonia emissions from grassland under various N-management regimes

Abstract

Materials and methods A field-plot experiment (2 x 1.5 m per plot, n=3) was carried out, with grass-derived and maizederived slurries of high and low dry matter (DM) content. Plots were spread using splash-plate application. In addition, one of the combinations of maize-derived slurry DM content was spread on three additional plots simulating trailing shoe, in order to compare both slurry application techniques. Control plots include no N fertilization and 60 kg N ha of calcium ammonium nitrate (CAN) fertilization. Two treatment applications were carried out in April and July 2009 under contrasting climatic conditions. Continuous flux measurements were taken after slurry application. Ammonia was measured using a photo-acoustic analyzer (INNOVA 1412 Trace Gas Analyser, INNOVA Instruments, Copenhagen, Denmark) coupled to a dynamic chamber. Carbon dioxide and nitrous oxide were measured using static chambers and an Infra-Red Gas Analyzer (CO2, PP Systems EGM-4, PP Systems, Hitchin, Herts., UK) or a gas chromatograph (N2O, Varian) for the analysis of the gases. Ancillary data (air and soil temperature, rainfall, soil moisture, soil ammonium and nitrate concentration) were also collected. Cumulative fluxes were calculated for the first week following fertiliser application (Figure 1). Background fluxes (control plots) were subtracted from fluxes calculated for treatments plots. These treatments were compared using ANOVA with slurry dry matter and slurry types as main factors.