Perennial pasture grasses such as natives, temperate perennials like phalaris, and tropical grasses are generally more productive if coexisting with legumes, or if their nitrogen supply is added to via fertiliser.
It is commonly more difficult for annual legumes, like sub clover and medics, to reliably thrive with perennial grasses than when grown more or less on their own in an annual only pasture.
However, the perennial grass has so many advantages, such as deeper root systems and better able to use deep soil water, extends growth period, and can restrict or prevent creeping soil acidification without the need for periodic liming.
A common requirement for perennial pastures is species and varieties that are long-term persistent.
There is ample evidence that well managed native grasses are long-term persistent.
Also, well managed tropicals have commonly persisted well for more than 30 years, even in drier environments.
Temperate perennials, if well managed, can persist indefinitely in favourable rainfall and higher elevation areas.
However, as environments become hotter and drier (outer slopes, plains) persistence is more of an issue. Because persistent types are more summer dormant, their usefulness in extending growing seasons is less.
Perennial grasses, whatever the type, require good soil nitrogen to be efficient growers (turn moisture into feed) and to provide quality feed.
Two main strategies are available to provide them with nitrogen. Successfully grow them with a legume, generally (but not the only option for some environments) a winter annual one. Secondly, supply their nitrogen supply via fertiliser. Or use a combination of both.
I use our central west NSW property as an example. About 50 per cent is tropical grass based and 30 per cent native perennial grass (the remainder dual purpose crop).
Winter legumes grow in all the pastures, but because of extra competition for water from the perennials, their contribution to autumn winter and spring feed can be compromised compared to what might occur in a winter legume only pasture.
But the advantage of perennials (especially tropicals) as part of the pasture, is that they respond quickly to so called out of season rain such as early autumn, late spring and summer where annual winter legumes have hayed off or its too early for them (early mid-autumn) to commonly supply useful feed.
Annual legumes as part of perennial pastures, while less legume productive than when in an annual only pasture, it is important to appreciate their value in good seasons provided long-term persistent species and varieties are grown.
For example we were able to cut valuable hay from them in 2016. Their soil nitrogen building in a good year contributes to grass nitrogen supply well beyond the last good winter season.
Adding nitrogen to perennials is becoming more mainstream and can be an excellent investment should winter legumes have had a bad run of years, or it has proven difficult to grow them with perennials, especially in more western environments.
Improving legume persistence in perennial pastures can be helped in slopes and plains environments, if earlier maturing hard seeded varieties are used.
- Bob Freebairn
Research, such as Tamworth DPI studies led by Dr Suzanne Boshma, has shown that in a nitrogen deficient situation, 50 kg/ha nitrogen can produce an extra 7500kg/ha tropical grass for less than $50. Hay, silage or grazing, a great investment.
In our example, we tend to top-dress tropical grasses with nitrogen after a poor winter spring when legume contribution has been low.
Native grasses can also respond to top-dressed nitrogen, but generally are far less efficient than tropicals.
Improving legume persistence in perennial pastures can be helped in slopes and plains environments if earlier maturing hard seeded varieties are used.
For tableland areas some research suggests still stick with hard seeded mid-maturing types.
Earlier maturing varieties may not be as productive as later maturing ones, but are more reliable seed setters in slopes plains areas, and often set far more seed in more moisture stressed springs where perennials are also after limited water.
Next week: Paddock variable altitude has a big impact on variety choice and ideal sowing time.
Climatic differences, especially minimum temperature and frost incidence, can be great over a given paddock with elevation variances of as little as 20-45 metres.
- Bob Freebairn is an agricultural consultant based at Coonabarabran. Email robert.freebairn@bigpond.com or contact (0428) 752 149.