121: Nitrous oxide emissions and grassland management

Petersen, Søren O. (2001) Nitrous oxide emissions and grassland management.^*

Summary

Nitrous oxide emissions and grassland management
Søren O. Petersen, Danish Institute of Agricultural Sciences, Dept. Crop Physiology and Soil Science, Denmark
Carbon storage in grasslands is a potentially important mitigation option in support of the Kyoto process. However, the effect of C sequestration by pastures depends significantly on the fate of N inputs via animal deposits, atmospheric N2 fixation or inorganic fertilizers, since N2O derived from N turnover can partly or completely off-set the removal of atmospheric CO2.
Urine spots have been identified as strong sources of N2O, but the quantification of N2O emissions from grazed pastures is complicated by temporal and spatial variability, and by limited understanding of the interactions between urine composition and N turnover. Information about relationships between N2O emissions and soil conditions (compaction, moisture, soil water chemistry, microbial community dynamics) in grazed pastures could help predict emission potentials via modelling.
This presentation describes planned field experiments to characterize the spatial and temporal distrubtion of N2O fluxes during the grazing season in 1, 2 and 8 year old pastures, as well as the associated N turnover (via 15N) and microbial dynamics (via PLFA analyses). The experiments, which include intensively sampled spots with urine of varying composition, as well as fields rotationally grazed by dairy cattle at two stock densities, contribute to the FP5 project ’Greenhouse Gas Mitigation for Organic and Conventional Dairy Production’ (MIDAIR) and to the Danish project ’Dinitrogen Fixation and Nitrous Oxide Losses in Organic Grass-Clover Pastures: An Integrated Experimental and Modelling Approach’.

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