peer-reviwedGrazed clover/grass pastures are important for animal production systems and the clover
component is critical for its contribution to N inputs via biological fixation of atmospheric
N2. The resource efficiency and environmental emissions for clover/grass pastures can
differ from that of N-fertilised grass-only pastures. Fixation of N2 by clover uses photosynthetically-
fixed carbon, whereas fertiliser N production consumes fossil fuels and
has net greenhouse gas (GHG) emissions. Clover has a higher phosphorus (P) requirement
than grass and where extra P fertiliser is used for clover/grass pastures the risk of
P loss to waterways is greater than for grass-only pastures. Nitrogen leaching from
grazed pasture increases exponentially with increased N inputs and urinary-N contributes
70 to 90% of total N leaching. However, the few studies comparing clover/grass and
N-fertilised grass-only pastures at similar total N inputs indicated similar N leaching
losses. Nitrous oxide emissions from grazed pastures due to N-cycling of excreta are
similar for clover/grass and N-fertilised grass-only pastures at similar total N inputs.
However, grass-only pasture requires the application of N fertiliser, which will result in
additional specific losses that don’t occur from clover-fixed N. Thus, total N2O emissions
are generally higher for N-fertilised grass pastures than for clover/grass pastures. A summary
of various whole-system and life cycle assessment analyses for dairy farms from
various countries indicated that at similar total N inputs, clover/grass pasture systems
can be more efficient than N-fertilised grass systems per kilogram of milk produced from
an energy use and GHG perspective whereas results for nutrient losses to waterways were
mixed and appear to be similar for both pasture types. In practice, other management
practices on farm, such as crop integration, supplementary feeding strategy and winter
management, can have a larger overall effect on environmental emissions than whether
the N input is derived from fertiliser N or from N2 fixation
