Summary. This study aimed to define the effect of
differing rates of nitrogen application and lock up length on harvested
material for silage in south-western Victoria. At 2 sites in south-western
Victoria, 140, 3 by 2 m plots of predominantly perennial ryegrass pasture were
randomly allocated, within 4 replicate blocks. Five nitrogen fertiliser rates
(0, 25, 50, 75, 100 kg N/ha) in combination with 7 lock up lengths were
randomly allocated to the 35 plots within each replicate. Nitrogen was applied
1 week after initial lock up (September 10, site 1; September 12, site 2) and
harvesting commenced 3 weeks after initial lock up. For each treatment and
harvest date, dry matter yield and botanical composition were determined and
samples of total pasture and the ryegrass fraction were collected and
chemically analysed for dry matter digestibility, crude protein, neutral
detergent fibre, water-soluble carbohydrates and mineral content.
Metabolisable energy was derived from dry matter digestibility.
Increasing rates of nitrogen increased herbage dry matter yield regardless of
length of lock up. The yield response was greatest 8 weeks after initial lock
up at both sites (site 1, 26 kg DM/kg N; site 2, 14.9 kg DM/kg N).
Subsequent regrowth of pasture was increased by nitrogen application over
shorter lock up lengths (weeks 3 and 4). Botanical composition was unaffected
by treatment during the harvesting period or in the subsequent autumn.
Application of nitrogen gave rise to a linear increase in pasture
metabolisable energy and crude protein content at both sites until week 5.
Thereafter, this response diminished and by week 8 there was a decrease in
metabolisable energy and crude protein content. Neutral detergent fibre
content was relatively unaffected by nitrogen application until week 8 of the
study, at which point there was a linear increase. Application of nitrogen
reduced the water-soluble carbohydrate content of pastures throughout the
sampling period.
It is concluded that application of nitrogen to a mixed sward locked up for
silage can increase dry matter yield and, provided pasture is harvested before
ryegrass ear emergence, can also have a positive effect on metabolisable
energy and crude protein. Given that the decision for removing paddocks from
the grazing rotation is based upon pasture growth and stocking rates, the use
of nitrogen fertilisers on higher stocked farms could lead to increased dry
matter yield over shorter lock up periods. On farms with lower stocking rates
shorter lock up periods may allow for pastures to be returned to the grazing
rotation earlier, or provide the opportunity for a second harvest of pasture
for silage.
Effects of Planting Time and Nitrogen Application on Dry Matter Yield of the Forage Rice Cultivar Tachiaoba in Southwestern Japan