WITH perennial ryegrass being the cornerstone of our dairy systems, it is no surprise that there is a lot of emphasis on its persistence.
Ideally, you would sow a pasture once and never need to sow it again. Unfortunately, that is not reality.
There are many factors that affect persistence.
It is sometimes thought that it is purely the cultivar selection that is important.
However, consideration also needs to be given to other factors that have a big influence on pasture persistence.

Growing conditions
Environmental conditions have a big impact. The big ones are heat and moisture stress.
We are all too aware from recent years of how pastures thin out when it’s too wet or too dry.

Management
Both over-grazing and under-grazing can open up pastures to competition. Plants need time to recover after grazing. Weakened plants are more likely to die.
Pugging and long paddock lockups for silage or hay can decrease plant numbers enormously – these gaps will eventually be filled with new plants.
What fills the gaps largely depends on the seeds present in the soil, which species are favoured by the growing conditions and soil fertility, hopefully not weeds.
The pastures with a history of good weed control (weed seed burden is low) will generally get the desirable pasture species to fill the gaps rather than weeds.
It is generally difficult to eradicate aggressive weed species in a one off re-sowing program.
Generally some weed plants or seeds persist through an initial renovation program.
Renovation technique is important for minimising the problem.
Let’s face it, some plants are just well suited to our growing conditions and it can be a battle to maintain ryegrass dominance over many years.
Multiple cropping is often used to get on top of tough weeds such as bent grass or distitchum in problem paddocks.
Sometimes the long path to success needs to be taken.
A major contributor to less plant density in autumn is over grazing over summer.
Use of extra supplementary feed, feed pads and sacrifice paddocks can substantially aid persistence.

Cultivar
While some cultivars will be more persistent than others, it is often thought that the older varieties are more persistent such as Victorian ryegrass.
There was an on-farm demonstration of large plots of perennial ryegrass cultivars under the same grazing management.
Grazing management targeted quality, with minimum seed head development.
Vic rye performed the worst. It is perceived “persistence” relies on a large seed drop. It highlights the role of seed recruitment in persistence.
The better you are at preventing any seed production, the less new ryegrass plants you are likely to get from seed recruitment.
Also, more persistent cultivars are likely to have more vigorous seedlings (they handle the competition better).
So there are many factors affecting pasture persistence (we haven’t even looked at soil fertility).
Think about all the management factors affecting pasture persistence and consider having some pasture renovation each year as part of the normal management of the feeding system.
The good news about renovating pastures is that you can get genetic gain, just like in your milking cows.