During 1993–94, the nutritive characteristics of white clover
(Trifolium repens cv. Haifa), ryegrass
(Lolium perenne cv. Ellet) and paspalum
(Paspalum dilatatum) were examined at weekly intervals
on 4 occasions. On each occasion, they were initially defoliated with a drum
mower and allowed to regrow for up to 9 weeks; dates of the 4 initial harvests
were 24 September, 26 November, 28 January and 25 March. The objective of the
part of a larger study that is reported here was to examine changes in
macro-minerals of the 3 species as they regrew after defoliation, in order to
start providing information for informed decisions on the need for
supplemental minerals in northern Victorian dairy systems.
The ranges in mineral elements recorded in this study were
0.16–0.43% for phosphorus, 1.18–3.41% for potassium,
0.26–1.49% for calcium, 0.20–0.54% for magnesium,
0.05–0.44% for sodium, 0.79–2.02% for chlorine and
0.15–0.37% for sulfur. A major reason for the large ranges was
due to variations between the 3 species. White clover was richer in a number
of minerals than were the grasses, particularly calcium, potassium and
magnesium, although phosphorus was also generally higher. Perennial ryegrass
had high sodium concentrations, which were probably related to high
watertables, with the associated propensity for salinity problems, that are
endemic in irrigated northern Victoria. It is suggested that, on the basis of
the pasture on offer, phosphorus is the major mineral that can potentially
limit milk production by grazing dairy cows in this environment, although
possible deficiencies were also demonstrated for calcium, sodium and sulfur.
Where a mineral has its highest concentration in the leaves, lax grazing
management or the use of short pastures should result in higher concentrations
in the pasture eaten than that on offer. Leaves were not always the richest
source of a mineral although this was almost always the case for all minerals
in ryegrass leaves. In white clover, phosphorus, calcium, magnesium and sulfur
were more concentrated in the leaves than in the stem. In paspalum, calcium,
magnesium and sulfur were more concentrated in the leaves. White clover stems
had higher concentrations of potassium and chlorine than leaves, while with
paspalum this applied to sodium and chlorine. It was concluded that the
species composition of a pasture will have a large impact on the supply of
minerals for grazing dairy cows, although the leaf : stem ratio, as determined
by time since the last defoliation, will also have a role in determining whole
plant composition.
Effects of the Harvest Stage of Maize Hybrids on the Chemical Composition of Plant Fractions: An Analysis of the Different Types of Silage
