Dinitrogen fixation and nitrous oxide losses in grass-clover pastures
Organic farming practices, and in particular dairy production systems, are becoming increasingly abundant within Danish agriculture. Grazed pastures may be a significant source of nitrous oxide (N2O), an important greenhouse gas, and N2O emissions from e.g. organic dairy farms may be smaller than from conventional systems. The difference in N2O emissions, however, may depend on the intensity, with which dinitrogen (N2) fixed by the legumes in grass-clover mixtures, are recycled in the grazed fields. Particularly urine induces N2O emissions, which also constitutes a major loss of N.
Because of the uncertainties in quantifying N2 fixation, no contribution from N2 fixation to N2O emissions from legume pastures has actually been estimated so far. Total N2 fixation estimates usually has not accounted for contributions from plant compartments below grazing-height. Inventories of N2O emissions for organic farming systems may therefore be severely biased.
The proposed work will investigate magnitudes and describe characteristics of N2O emissions, denitrification and N2 fixation in organically managed grass-clover pastures under different grazing intensities and variable sandy soil textures. Quantitative results will be implemented in submodules of a whole-farm N flow model. A number of field experiments will be initiated, supplemented by microcosm experiments under fully controlled conditions.
This project will provide information for a holistic evaluation of the environmental impact of organic farming practices. It will provide support for decision making by organic farming extension services. Finally, the project will supply information for the construction of inventories of greenhouse gas emissions.
I.13 Dinitrogen fixation and nitrous oxide losses in organic grass-clover pastures: An integrated experimental and modelling approach (DINOG)
Dr. Per Ambus, senior scientist
Risø National Laboratory, Plant Research Department
P.O. Box 49, DK-4000 Roskilde
Phone: +45 46 77 41 52; Fax +45 46 77 41 60
Finn P. Vinther, Søren O. Petersen, Jørgen E. Olesen and Nick Hutchings, DIAS