Galvanised burr a curse

There is no one approach to this challenge, but following a sound plan, with the capacity to modify as situations arise, is I believe, the way forward.

Both these pastures, improved and unimproved, were photographed in much the same season - similar in soil type and similar in seasonal conditions. Soil pH was around 5.6, texture a medium to lighter loam, natural soil phosphorus low to medium, but low sulphur. No known subsoil constraints exist other than moderate sodicity in the sub soil.

The economic benefits of improving a pasture like the galvanised burr paddock is great.

In a 600 millimetre average rainfall environment, like this example, carrying capacity of galvanised burr infested paddocks is around 2.0 dry sheep equivalent per hectare (DSE/ha) and largely restricted to enterprises not dependent on high quality feed.

In contrast, the improved pasture runs a fattening business on an average around 7.5 DSE/ha.

One approach to upgrading galvanised burr pasture is to leave it in its "natural" state but improve the competitiveness, as well as productivity, of palatable pasture plants, including native perennials.

A first approach for this strategy is soil test from an Australian accredited laboratory (e.g. NSW DPI, or a commercial one like Incitec/Pivot). If soil phosphorus and sulphur is low, consider applying a fertiliser like single superphosphate ahead of next autumn's break with seed of appropriate annual legumes (choice will depend on soil pH).

Galvanised burr can be killed via herbicides such as 2,4-D but these can badly damage any present naturalised or introduced legumes. Once legumes have hayed off in spring and following a reasonable rain these herbicides can achieve useful weed kills but not damage grasses.

Another approach to thinning weeds like galvanised burr is physical damaging them via slashing or stubble busting type implements. While nowhere near a total kill such damage to them allows native grasses and legumes to capture more sunlight, space and better compete with weeds.

Commonly, bad weed infested paddocks are large and set stocked for long periods.

Palatable useful species, like many native grasses, are constantly grazed whereas unpalatable weeds are hardly grazed at all. Hence, weeds like galvanised burr come through droughts often unscathed but native perennial populations can be decimated.

Part of reviving badly weed infested paddocks with improved native grass density can involve additional subdivision so that paddocks can be better managed.

Periodic rest and allowing perennials to recover and build root reserves is an important management aspect. Also allowing desirable plants to periodically set seed improves opportunities for faster rebuilding of their populations, again provide rest periods for their establishment after good rain events occur.

Another approach to attacking weeds like galvanised burr is to crop them, even via zero till, for three years, to eliminate parent plants and drive down the soil weed seed bank, and then establish a tropical perennial grass pasture combined with winter legumes.

While it sounds expensive and time consuming, this approach can be relatively inexpensive, and a well-established and managed stand can last indefinitely.

A cropping phase prior to pasture establishment generally can more than pay for itself, either grain only, dual purpose or grazing. Timely and effective control of weeds in the fallow, as well as in-crop, is an important part of weed control and pasture establishment.

Some tropical grass stands, once badly galvanised burr infested, remain weed free 30 years after establishment. And provided soil fertility is maintained they remain productive and profitable.

Next week: 50 years of tillage research shows resilience of zero till.