Nitrous oxide emissions from grazed grassland: effects of cattle management and soil conditions

Summary

Traditionally, dairy cattle spend a substantial part of the year on pastures. For organic farming within EU it is specified that ”all mammals must have access to pasturage or an open-air exercise area” which they must be able to use whenever ”weather conditions and the state of the ground permits” (Council Regulation [EEC] No 2092/91 ).
Dairy production systems are characterized by a considerable N surplus, and N deposited during grazing represents a significant risk for environmental losses, including N2O emissions. Excess N is excreted mainly in the urine, the composition of which is influenced by factors such as lactation stage, sward quality and intake of supplements. Resulting N concentrations in urine patches can range from 20 to 80 g N m-2, and soil environmental conditions associated with such a range of N inputs could affect the potential for N2O production via nitrification and denitrification. Soil properties and fertilization also influence N2O emissions.
This presentation shows results from a work package within the MIDAIR project which aimed to describe known sources of variability within the grazing system, and their impact on N2O emissions. The objective was to evaluate if management changes can be proposed that will reduce the risk for N2O emissions associated with grazing. Field studies have addressed the heterogeneity of soil physical, chemical and microbiological properties, while plot-scale and laboratory experiments have examined the fate of urinary C and N and the microbial response to urine deposition.