Dr Michael Widderick
PHOTO: Cox Inall Communications
All that is old is new again: vinyl records, paper books, tillage. After seemingly being consigned to history by the clear advantages of reduced-tillage systems, tillage has reappeared in growers’ thinking as it becomes apparent that certain weeds are prospering under herbicide-only management.
If it comes back, though, the new tillage will not be your father’s tillage.
Minimum tillage has amply demonstrated that the less soil disturbance in cropping systems, the better. The future of weed control looks to lie in technologies that integrate the best of chemical control – such as weed detection systems – with on-the-spot strategic tillage.
Queensland Department of Agriculture and Fisheries (DAF) principal research scientist Dr Michael Widderick says it is clear from his GRDC-supported research that continuing to rely wholly on chemical control is not an option.
“The spread of no-till farming has meant that almost all weed control now revolves around herbicides,” Dr Widderick says. “As a result, the weed spectrum in the northern grains region, for example, has changed to favour herbicide-resistant, surface-germinating weeds like common sowthistle, fleabane and feathertop Rhodes grass.
“If we continue to rely only on herbicides, we continue to favour the evolution of these weeds, and other herbicide-resistant species will inevitably appear.
“The challenge is to identify ways of using tillage that retain the benefits of zero-till while addressing weed-management issues.”
Tillage presents a mixed bag of benefits and problems. Aside from damaging soil structure, its effects differ across weed species. Burying seed can prevent weed germination, but it generally also preserves seed viability.
In one Queensland DAF trial, virtually all barnyard grass and liverseed grass seed became unviable after two years on the inhospitable soil surface, but at least 10 per cent of seed survived when buried at a depth of 10 centimetres.
To assess the effects of tillage on weed ecology, Queensland DAF has conducted four GRDC-supported field experiments since 2011. The studies have looked at weed emergence under zero-till compared to treatments using harrows, a Gyral cultivator, offset discs and one-way discs.
Seeds of awnless barnyard grass, feathertop Rhodes grass, windmill grass, liverseed grass, common sowthistle and flaxleaf fleabane were sown on the soil surface before tillage was used.
Small glass beads were used to track the degree of soil inversion and seed movement under different tillage methods. As expected, the greater the tillage intensity, the more beads buried at depth (5 to 20cm).
Dr Widderick says tillage treatments proved most effective on small-seeded species such as fleabane and common sowthistle. The greater the tillage intensity, the lower the subsequent weed emergence across all species.
The one-way disc, the implement causing the greatest amount of soil inversion, also proved the most effective at hindering seed emergence.
However, the results were complicated by different results in different seasons. In seasons that started hot and dry, under zero-till, weed seeds near the soil surface were punished by the conditions and lost their viability. The harrows and Gyral machine buried seed deep enough to preserve its viability, but not deep enough to stop emergence when the season broke.
Considering all the data, Dr Widderick believes that answers to the weed challenge lie midway between the two systems; perhaps by harnessing technologies such as robotics to deliver tillage only where necessary.
“For example, we may see robot rigs equipped with weed-detection sensors and dual-equipped with the ability to selectively apply herbicide or tillage treatments,” Dr Widderick says.
“If the unit detects a grass weed, it may apply tillage. If the robot detects a broadleaf weed, it may apply herbicide.”
He says if robotic systems are capable of delivering it, tillage may yet return to Australian paddocks – but not via those one-way ploughs rusting behind many farm sheds.
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GRDC Project Code
UQ00062, UA00124, UWA00171