How to restore pasture health following drought

How to restore pasture health following drought


Cropping
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We have had some terrible droughts in the past, in many cases as bad as the current one, with some pastures recovering well and some taking for ever or needing re-establishment.

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A once degraded native pasture, similar to the photograph below. Careful grazing management, correction of soil fertility, and a return to a good season resulted in excellent pasture recovery.

A once degraded native pasture, similar to the photograph below. Careful grazing management, correction of soil fertility, and a return to a good season resulted in excellent pasture recovery.

We have had some terrible droughts in the past, in many cases as bad as the current one, with some pastures recovering well and some taking for ever or needing re-establishment.

Firstly, winter legumes like sub clover, medics, serradella and the like.

Commonly, varieties with a lot of "hard seed" and that had built up a good soil seed bank, for example from the 2016 spring in many areas, have the potential to regenerate well after two or three consecutive years with next to no spring seed set (for example 2017-18).

In areas that have received a reasonable to good autumn break, we are already commonly seeing many good winter legume establishments.

Where winter legume soil seed bank may have been low leading up to the autumn break, for example because of insufficient build up in previous years, it is valuable to check established density.

If low establishments exists, or occurs, for example three or four legume plants a square metre, it is possible to manage these for relatively quick seed build-up if seasonal conditions become/remain reasonable through to spring.

Overgrazed bare pastures take a lot of nursing and a lot of time to fully recover. Ideally manage to build drymatter levels sufficient to prevent rapid rain runoff.

Overgrazed bare pastures take a lot of nursing and a lot of time to fully recover. Ideally manage to build drymatter levels sufficient to prevent rapid rain runoff.

One winter legume plant of most species has the potential to set hundreds of seeds.

Care must be taken to ensure these plants are not grazed too hard over winter, and perhaps not grazed in spring until after seed set, unless the season is extremely favourable.

Whatever the density of winter legumes, and other winter herbage such as annual grasses like ryegrass, maximum winter/spring growth occurs if plants are allowed to develop reasonable leaf area.

While this can mean less early grazing (after the autumn/winter break) it generally means far more later winter and spring grazing.

Potential dry-matter production relates to amount of leaf area able to access sunlight and deeper roots from more developed plants.

If winter legumes are almost non-existent, it commonly is best to reintroduce them into the pasture, preferably by direct drilling. If adding before the autumn/winter break, topdressing is a crude but often effective way if good follow up rains occur.

Winter legume growth is also dependent on soil deficiencies like phosphorus and sulphur being corrected, if they exist. Nutrient deficient pastures grow little winter feed and build little soil nitrogen for companion grasses.

It is also important that the correct strain of rhizobia bacteria coexists with the legumes. In some cases, rhizobia may need reintroducing.

If re-sowing, adding earlier maturing hard seeded varieties of suitable species may also be a good strategy.

If winter legumes are almost non-existent, it commonly is best to reintroduce them into the pasture, preferably by direct drilling. - Bob Freebairn

Lucerne pastures have commonly declined, both in density and vigour over the drought. Provided more than seven plants a sq/m have survived (less in drier western districts) these can often be nursed back to good productivity.

Lucerne requires good recovery periods to rebuild root reserves and ideally should be grazed off in relatively short periods, to continually provide root reserve build-up.

Like most plants, recovery and productivity will be greater if not grazed to the ground. Lucerne density is hard to rebuild if depleted.

For thin stands, sooner or later a decision will be required to plan for reestablishment, preferable after a crop phase to reduce likely weed disease and pest issues.

It is also difficult to thicken up temperate perennial stands (phalaris, cocksfoot, fescue, rye) if populations have fallen too low.

Rotational grazing and not flogging into the ground help individual plant recovery.

One highlight of the drought has been the high survival rate of tropical perennial grasses.

This is provided they went into the drought in strong condition, they were not continually grazed into the ground, opportunities were given to regrow after periodic (although mainly low) rainfall events, and varieties were suitable for the soil and area.

In contrast to lucerne and commonly temperate perennials, tropical perennials, including many native perennial grasses, can thicken up post drought if sound grazing management is practised.

Not grazing into the ground, recovery periods for seeding and new plant recruitment, and good soil fertility are part of the recovery story.

Next week: Best annual legumes to smother pasture weeds.

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