Managing new pastures
Tom Farran, DEPI Tatura
Most dairy farms will have sown some new pastures this autumn. For these new pastures to perform to their full potential they need to be well managed.
One of the most crucial times to get the pasture management right is during the establishment phase through until after the first grazing. The following outlines some important information on the early management of pastures and how to introduce them into the herd's diet.
Early Grazing Management
Young ryegrass plants use much of their stored energy to produce new leaf growth. The plant relies on these new leaves to capture energy from the sun to produce more leaves, support root development and replenish their store of energy reserves. If pastures are grazed too early, too short, or too frequently when growth is just beginning, then the ryegrass plant will have reduced energy reserves and a diminished ability to capture sunlight.
The overall result of grazing too early or too often will be a pasture that is slow to regrow, with increasingly smaller leaves. This means a longer interval between grazing will be required, and less feed will be in the paddock each time. Pastures will not thicken up and weeds will have a greater chance to infiltrate the paddock. The result will be a weaker, weedier pasture with a reduction in the overall dry matter production over the year.
When to Graze?
Science has shown that a newly-sown ryegrass pasture can sustain more than three actively growing leaves before the first grazing (but not in subsequent grazings). The new seedling will also tiller very well without needing to be grazed to stimulate tillering. The once common advice of giving new ryegrass pasture a quick, light grazing to stimulate tillering will actually have the reverse effect. It will reduce the amount of tillering due to depleting the plant's energy reserves. Until the plant reaches the 'canopy closure' stage, it will continue to tiller and accumulate more high quality feed at an exponential rate. Canopy closure refers to when the pasture has grown to the stage that the ground can no longer be seen from above without first having to part the pasture.
Once canopy closure has been reached the bottom leaves will start to decay, quality will begin to decline, tillering will reduce and net growth rates will begin to decline. In theory, this means it is better to leave the new plants to grow out close to canopy closure before they are grazed. However if you have a large area of new pasture all ready to graze at once, then it may be necessary to start grazing some of it early to make sure you get to the end before canopy closure.
If a paddock has been oversown, the new seedlings could easily be shaded out by the existing ryegrass plants, so in this case it will need to be grazed earlier to ensure that this shading does not set the new seedlings back. It is a compromise.
It is also important to check that the new pasture is ready for grazing by doing the 'pluck test'. Make sure that the new ryegrass plant will not pull out of the ground when pulled up by hand, i.e. the leaves tear off rather than the roots pull out of the ground.
Getting the Residual Right
It is important to avoid overgrazing young ryegrass plants as the energy reserves that are used to produce new leaf growth after grazing are located in the bottom 4-6cm of the plant above the ground, not in the roots as was once believed. By grazing below this level the plants are being deprived of their energy reserves and as a result new leaves will be much smaller, yet still take the same amount of time to grow.
It is often very difficult to get the cows to leave a 4-6cm residual at the first grazing. This new pasture is of high quality right to the ground as there is no 'residual' sheath that was left behind from last grazing. As a result cows will find it easy to graze the new pasture hard. In many cases the best and/or only option is to use the on-off grazing technique. This is where the cows are put onto the grazing area for a short period, and then removed from the paddock as soon as they have grazed down to the desired residual of 4-6cm.
One of the most crucial times to get the management of pastures right is during the establishment phase through until after the first grazing. Waiting until the new pasture has nearly reached canopy closure prior to grazing will optimise tillering and growth.
It is very important to make sure the cows leave a residual of 4-6cm behind after grazing as this is where the energy is stored for the plants to regrow. Managing the early stages of the pasture's life is vital to having healthy, dense and productive pastures.