Nitrate leaching losses from intensively managed monoculture grass
and grass–clover pastures were
measured during 1994–96 at a long-term experimental farm in south-west
Scotland. Field-size
lysimeter plots were established in 1993 on the existing pastures on a
silty clay loam non-calcareous
gley. No fertilizer-N was applied to the grass–clover, while the
monoculture grass was fertilized with
c. 240 kg N ha−1 year−1, but
both swards received 2–3 cattle
slurry applications annually
(120–390 kg total N ha−1 year−1).
The pastures supported 2–3 cuts for silage conservation, and were
grazed by dairy cattle and stocked with sheep during the winter months.
Initially, leachate nitrate concentrations from the fertilized grass
were considerably larger than
those from the clover-based pasture, but became similar with time. The
annual nitrate leaching losses
from the grass–clover (24–38 kg NO3-N ha−1)
were less than that from the monoculture grass
(30–45 kg NO3-N ha−1), but the
differences were not large considering the additional fertilizer-N
applied to the latter treatment. Results also suggested that greater leaching
losses occur during a
warmer, drier year, compared to a cooler, wetter year, regardless of the
source of N-input.