Down to Earth: Legumes key to perennial productivity

Down to Earth: Legumes key to perennial productivity


Cropping
An autumn 2014 view of a strong native grass pasture with annual legumes adding greatly to autumn winter feed and supplying nitrogen for the perennial grasses. Sound management ensures native perennials and winter legumes contribute to healthy soils and long term persistent productive pastures.

An autumn 2014 view of a strong native grass pasture with annual legumes adding greatly to autumn winter feed and supplying nitrogen for the perennial grasses. Sound management ensures native perennials and winter legumes contribute to healthy soils and long term persistent productive pastures.

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OUR property in a typical 625 millimetre average rainfall year has, as its grazing components, native perennial grass-based pastures, tropical perennial grasses and dual purpose winter cereals.

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OUR property in a typical 625 millimetre average rainfall year has, as its grazing components, native perennial grass-based pastures, tropical perennial grasses and dual purpose winter cereals.

All must be productive and nutritious for our finishing business.

A client recently told me he did not fertilise his native pastures as he understood it would lead to perennial grasses disappearing, broadleaf weed problems, soil becoming more acidic as well as declining soil health.

These are all aspects promoted by some people, sometimes paid from the public purse, which unfortunately leads to poor quality native pastures, although they may be diverse and persistent.

Inappropriate grazing management can lead to weeds and loss of native grasses as a consequence of fertiliser and the adding of legumes.

However, technology is available to have healthy persistent native perennial grass pastures that are productive, high quality, have little impact on soil acidity as well as enriching soil quality.

Spring grazing is an important management aspect when legumes are added and fertiliser is used to correct soil deficiencies.

In a good winter, spring season fertiliser and clovers can be very productive, producing several tonnes a hectare of dry matter.

A couple of good seasons in a row can lead to thinning out of native grasses if the legumes are not grazed down to about three to 2.5 t/ha of dry matter.

Too much clover that isn't grazed down tends to shade out the often dominant summer active native grasses at the time they normally begin to regrow.

Clovers and other herbage like annual ryegrass restricted to below 3t/ha still represent a lot of feed, but generally are sufficient to allow light into the regrowing native grasses.

Sound grazing management of native grasses is also important as it allows them to be strong and better able to cope with increased spring competition.

A system of flexible rotational grazing that allows periodic rebuilding of root reserves and an opportunity every now and then for new perennial grass recruitment helps ensure a strong continuing stand.

Not grazing perennial grasses into the ground also helps persistence.

Using earlier maturing annual legumes with native grasses has two advantages.

Earlier maturing types tend to produce less bulk in good springs and are therefore less smothering. Equally important is that they more reliably set seed in difficult springs as they flower and seed down before moisture stress commonly becomes too great.

Broadleaf weeds in native grasses are often a consequence of thinner, poor vigour native perennial grass plants. If you can manage to have strong perennial grass plants, broadleaf weeds are less likely to be a major issue.

Research in recent years has shown pasture and crops that grow well enhance soil characteristics like organic matter levels and biological biomass better than poorly growing ones.

If fertiliser is required to correct soil deficiencies in a well-managed pasture, it will contribute to improved soil health.

Soils that were mildly acidic in their natural state have tended to become more acidic with a system of annual crops and pastures.

However, improved perennial native pastures have tended to not change much in pH after many years of improvement via fertiliser, legumes and good grazing management.

To be productive and to provide good quality feed, native perennial grass pastures, like introduced ones, need a strong legume component.

The only alternative to these legumes providing the nitrogen is to add it via nitrogenous fertilisers.

Next week: Importance of high quality rainfall forecasts.

Bob Freebairn is an agricultural consultant based at Coonabarabran. Email robert.freebairn@bigpond.com or contact 0428 752 149.

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