- Keeping pasture cover within the optimal range of growth helps to achieve high growth rates, high utilisation, and high pasture
- The correct time to graze ryegrass is when there are 2.5-3 leaves per tiller. For rapid regrowth after grazing, keep post-grazing residuals above 1450 kg DM/ha.
- Understanding how ryegrass tillers grow gives better understanding of pasture management.
A perennial ryegrass pasture is made up of a population of ryegrass tillers. Tillers are found grouped together in clumps, each clump forming a ryegrass plant.
Tillers are largely individual although they do exchange nutrients to some degree.
Dairy pastures typically contain 3000-5000 tillers per square metre while sheep pastures contain 8000 or more.
New tillers are produced year-round with peak production from November to January.
A tiller has a single basal stem, a leaf sheath and a number of leaves. It can have only
three green growing leaves at any time.
Then a fifth leaf is produced, the second leaf dies, and so on. If pasture isn’t grazed, dead material (of little feed value) builds up in the base of the pasture.
How quickly do leaves grow?
The time it takes for a tiller to produce a new leaf varies, and is largely dependant on temperature (in winter) or moisture (in summer). In mid-spring a new leaf may be produced every 7 days while in mid-winter it may be every 17 days.
Tiller growth & yield
As a tiller regrows (as shown below) the initial growth rate is slow, and the first new leaf makes up only 15-25% of the potential yield of a pasture. Growth accelerates with the second leaf, and further with the third leaf production. Simply put, you are moving from one 'solar panel' or leaf to three. Grazing at 2.5-3 leaves per tiller captures most of this growth, with 40-50% of potential yield produced with the third leaf.
Re-growth & energy reserves
The regrowth cycle initially relies on the energy reserves plants store as carbohydrate in the basal stems. Immediately after grazing plants rely on these to provide energy for regrowth until the first new leaf is produced (see bottom diagram). With the first new leaf, photosynthesis then becomes the main energy source for growth of subsequent leaves as well as replenishing carbohydrate reserve stores.
When to graze
The optimal time to graze pastures to achieve both high growth rates and high pasture quality, is when tillers show an average of 2.5-3 leaves. To assess this in a pasture you need to check several tillers, as plants vary. At the correct stage you are looking for most plants to have a third leaf, some may be small, and others fully developed. By this stage plant reserves will have restored for plants to recover quickly from defoliation.
Note: Ignore older leaves left over from the last grazing (e.g in dung patches) or that have been partly grazed.
Grazing too early
Grazing before 2.5-3 leaves per tiller reduces both yield (middle diagram), and also regrowth as it is does not allow plant reserves to be fully restored. Grazing pastures at the optimum time is particularly important through summer dry periods, when plants are under stress. Nipping off the first leaf growth after rain, before tillers have 2.5-3 new leaves, can kill plants.
Grazing too late
If pasture is left to grow too long (>3500 kg DM/ha) it continues to produce new leaves, however older leaves die off (top diagram). Dying leaves accumulate in the base of the pasture which leads to:
- Reduced pasture ME - build-up of dead matter which is of lower feed value.
- Increased disease - long or dying pasture creates a favourable environment for pests,
- diseases and fungal spores (e.g. rust or facial eczema).
- Decreased pasture utilisation - due to the above factors.
- Reduced clover content due to shading.
Grazing too late usually happens in periods of rapid growth, when multiple paddocks are all ready for grazing simultaneously. Monitor growth closely; if necessary remove paddocks from grazing to cut for supplementary feed or pre-graze mow.
The secret to good grazing management is keeping pastures in the right 'grazing window' - keeping consistent post-grazing residuals, and pre-grazing at 2.5-3 leaves per tiller.