Getting the most out of your old perennial pastures
Lisa Warn, Lisa Warn Ag Consulting Pty Ltd
(This article has been reproduced with kind permission of the author)
The productivity and environmental benefits of having perennial grasses in pastures are well established. However, many so-called perennial pastures, particularly those well stocked with sheep, are really acting as annual pastures.
They tend to be dominated by annual species such as subterranean clover, capeweed or silver grass (Vulpiaspp.). In extreme overgrazed situations, they will be mainly capeweed and winter grass (Poa annua).
The end result is a pasture delivering well below its potential dry matter production and carrying capacity, and a high proportion of bare ground in late summer and autumn. Many producers think the decline in the perennial grass content is inevitable and resowing the paddock is inevitable.
However, there is no reason why many perennial grasses, especially phalaris, should not last indefinitely with the right management. Perennial ryegrass is perhaps the exception, where even with best practice management, dry years and soil pests (cockchafers etc) can reduce plant density.
Manipulate or renovate?
The high capital cost of resowing pastures means that it is not a decision to rush into. Before totally writing off a degraded perennial pasture, it is critical to explore any other low-cost opportunities to lift the performance of the pasture.
The first step is to collect some objective information about the number of perennial grasses per square metre surviving in the pasture. This will allow you to decide whether there is any point trying to manipulate the current pasture or whether it is a resow job.
The method I use is to walk a transect across the paddock (like you do when soil sampling) and throw out a quadrat (a 25 cm × 25 cm metre square) every 20–30 paces. Count the number of perennial grasses in the quadrat and multiply by 16, in this example, to convert plants per 25 cm2 to plants per square metre. Take at least 20 assessments for the paddock.
Often you will be surprised at how many desirable perennial grasses are present once you get down on your hands and knees to look closely. This is particularly true for phalaris, which tends to survive hard grazing and drought better than perennial ryegrass and cocksfoot.
For phalaris or cocksfoot pastures, if at least five – seven plants are present per square metre, don’t write the pasture off – there is an adequate base to work with. For ryegrass pastures, due to the smaller potential plant size, you would need at least 10 plants/m2.
Options for improving the perenniality of the pasture
There are two ways you can increase dry matter production from the perennial grasses in a pasture.
First, you can try to increase size and vigour of the surviving perennial grasses. Rotational grazing (focusing on achieving appropriate length of rest during autumn and winter) will allow the plants to increase their basal/crown area, dry matter production and root growth. Individual plants of Australian-type phalaris can spread sideways more than the winter-active cultivars.
However, the newer winter active variety, Holdfast GT, is more like Australian in its growth habit. This allows the cultivar to recover its density in the pasture after extreme events such as drought or overgrazing. The winter-active cultivars are more upright growing and less spreading, so rotational grazing can help restore their productivity. Phalaris will also tend to increase tiller size in response to rotational grazing, whereas perennial ryegrass and cocksfoot will increase the number of tillers per plant.
Getting the rest period right for the perennial grass species you are encouraging is the most important part of managing the rotation. Research shows that using ‘leaf stage’ as an indicator of when the grass is ready to graze in autumn to early spring will optimise the grass growth rates. Different species have a different maximum number of leaves per tiller that they can maintain before the oldest leaf starts to die off. Allowing a grass to regrow its maximum number of leaves per tiller after grazing will optimise photosynthesis, storage of carbohydrates, root growth and dry matter production.
There are two ways you can increase dry matter production from the perennial grasses in a pasture.
For perennial ryegrass and fescue, the target is to graze at the three-leaf stage; for phalaris and cocksfoot, the target is to graze at the four-leaf stage. If soil moisture is not limiting, the time it takes for grasses to regrow to their target leaf stage will be driven by the temperature at the growing point. So, the rest period may need to be 30–40 days in autumn, 40–60 days in winter and 15–25; days in spring. For best results, the rest period should be varied during autumn-early spring in response to rate of leaf emergence, and not based on fixed time intervals.
The Broadford Grazing Experiment (1994–2003) demonstrated how a rundown Sirosa phalaris pasture (which was sown in 1988) could be transformed with implementation of rotational grazing and adequate fertiliser. The pasture had only five phalaris plants per square metre at the start of the experiment, but the phalaris content increased to make up 60–70% of the pasture.
The second way to increase dry matter production from perennial grasses is to increase the numbers of perennial grasses in the pasture by encouraging seedling recruitment. This is a realistic option for cocksfoot or perennial ryegrass pastures, which ‘recruit’ seedlings more readily than phalaris.
This tactic involves removing stock over late spring–summer to let surviving plants run to head and drop seed, and then resting the paddock after the autumn break to allow the seedlings to establish. This is the mechanism by which old Victorian type perennial ryegrass pastures can recover from drought events. Early flowering cultivars (such as Victorian) have a chance to drop some seed if the season cuts out early, so even if the plant dies, new seedlings can establish the following year.
Don’t overlook soil fertility as a potential factor limiting the productivity of the perennial grasses.
The net result of having either larger or more numerous perennial plants per square metre is to occupy more space in the pasture, which will reduce the proportion of the pasture that is annual species. Obviously, you want to keep adequate sub-clover in the pasture; aim for a spring pasture composition of 40% clover and 60% grass.
Don’t overlook soil fertility as a potential factor limiting the productivity of the perennial grasses. If high-fertility species such as capeweed dominate the pasture, the grazing method is more likely to be holding back the perennials. A soil test will pinpoint any macro nutrient deficiencies. Dominance of silver grass can be linked to nitrogen deficiency, so make sure the clover growth and nitrogen fixation is not being limited by a trace element deficiency like molybdenum.
Value of new cultivars
Even if there are enough perennials surviving in the paddock to have a go with pasture manipulation, newer perennial grass or clover cultivars may offer some advantages over the old cultivars you have in your paddocks.
For example, the winter-active cultivars of phalaris produce around 50–100% more winter feed than Australian and Uneta phalaris. Once again, because of the capital costs of establishing pastures, you must be confident you are going to achieve a significant lift in stocking rate to make the exercise profitable.
If there are still opportunities to improve the performance of your current pasture, exhaust these options first. The winter growth of old Australian phalaris pastures can be lifted by using gibberellic acid in winter. If old cultivars have not performed well or survived on your farm, don’t expect new cultivars to do any better if there is an underlying issue with soil fertility or grazing management.
Spring pasture assessments
As well as being the time for soil testing, spring is also a good time for auditing pasture composition (on a percentage dry matter basis) and perennial grass density (plants/m2) in paddocks.
A comparison of the pasture data with stocking rate records for the paddocks will allow you to identify paddocks that are letting you down, and to prioritise action and expenditure. Analysis of these objective data from the paddocks will help you to make decisions about where to get the best return per dollar invested.
At a glance
- resowing pastures has a high capital cost – there may be opportunities to improve degraded perennial pastures at a low cost
- if you can find five to ten perennial grass plants per square metre – manipulate; don’t renovate the pasture
- the latest cultivars may be more productive, but you may not have optimised the productivity of current cultivars on your farm.
The Pasture Trial Network is developed and hosted by Meat & Livestock Australia, that compiles the data from independent trial sites of a range of pasture varieties.
It can be used to compare the performance (seasonal and total dry matter production) of tested varieties of legumes and grasses.
So, if you intend to sow new pastures, have a look at the performance at localities relevant to your environment.