to reduce the environmental impact of production systems, there is an increased focus on enhancing the sustainability of
advantage as the majority of ruminant feed requirements can
be met by grazing and/or conserved forage.
In Ireland, 95 per cent of grass seed sales are accounted for
by perennial ryegrass (PRG). Pastures are re-sown with PRG-
only mixtures, or PRG plus small quantities of white clover to
increase grass production due to its potential to yield high
quality and quantities of forage for grazing ruminants. However,
nitrogen (N) fertilisers are applied.
However, N fertiliser is volatile in price and, during high price
periods, can erode the competitive advantage of PRG swards
in sheep production systems. Excess application of N can be
harmful to above- and below-ground biodiversity, to the soil and
to nearby water sources, so investigation of alternative methods
to meet or reduce the N requirement of the sward is merited.