Grains Research and Development

Soil renovation

Research digs deep for soil renovation

Department of Agriculture and Food researchers along with local growers in the northern agricultural region, have demonstrated significant crop responses to soil inversion using mouldboard ploughs and partial inversion using rotary spaders in non-wetting sands.

At a glance

A study of mouldboard ploughing showing new growth on left next to an untreated area of scant growth. 
  • Department of Agriculture and Food research into soil inversion techniques is showing improved soil characteristics, in particular the removal of compaction, and amelioration of soil water repellence.
  • Complete soil inversion using the mouldboard plough has demonstrated weed control of more than 90 per cent.
  • Positive results and strong support from growers will allow further research to investigate the long-term consequences and how it can complement a minimum tillage system.

Results from the department’s 2009 field trials revealed the initial impact of mouldboard ploughs and rotary spaders was to remove soil compaction to the depth of working. Other benefits included improved weed control, and the amelioration of soil water repellence.

Department research officer Dr Stephen Davies said cultivation using mouldboard ploughs and rotary spaders fundamentally changed many soil properties and provided an opportunity to incorporate amendments, such as lime and clay; reduce water repellence; reduce compaction; increase soil pH; and distribute organic carbon and nutrients throughout the soil profile.

Rotary spaders combine a degree of soil inversion with soil mixing while the mouldboard plough completely inverts the soil profile in the top 25–30cm.

Dr Davies’ Grains Research and Development-funded research trials are the first to compare the two inversion techniques and suggest the use of mouldboard ploughs and rotary spaders could complement a minimum-tillage system. They also indicate that soil inversion could be carried out one in every 10 years.

Mouldboard ploughing

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The average yield increase using the mouldboard plough in the first year was 400–500kg/ha in cereal crops. The results demonstrate that some of the early crop growth benefi ts from mouldboard ploughing may be derived from a soil loosening effect, similar to that obtained from deep ripping. There are also a number of other agronomic advantages and the plough alters the soil profile far more than a deep ripper.

The trials show soil inversion could remove water repellence, raise subsoil with higher clay content in some soil types and provide an opportunity to alter the subsoil pH. The distribution of carbon in the soil profile substantially changes with increased organic carbon contents in the 10–20cm and 20–30cm layers while organic carbon in the 0–10cm layer is much reduced.

Mouldboard ploughing can also almost completely control weeds by burying weed seeds. If the mouldboard plough is set up for complete soil inversion, weed control of more than 90% can be achieved.

“However, these statistics should not disregard the importance of sound integrated pest management practices, which will need to continue to be implemented,” Dr Davies said.

While the softness of mouldboard ploughed soils can create crop establishment problems, Dr Davies observed that a number of growers had successfully established cover crops using simple methods, which involved spreading seed on the soil surface and then rolling it in with coil-packers or something similar.

Rotary spader

Like the mouldboard plough the spader also loosened the soil to the depth of working, changed the distribution of organic matter in the profi le, reduced water repellence and lowered weed populations. But compared with the complete soil inversion of the plough, the impact on these soil and agronomic properties was not as great. For example, the rotary spader method only controlled up to 60–70% of weed seeds and the soils still often remained partially water repellent after spading.

The spader does have its advantages though.

“It can incorporate clay-rich subsoil into water repellent sands and lime into acid subsoils, whereas the mouldboard plough completely buries these amendments rather than mixing them through the soil,” Dr Davies said.

The research reveals that particular care will need to be taken not to bury the clay-rich subsoil so deep that the effect of ameliorating topsoil water repellence is lost when incorporating it with the rotary spader.

Test of time

Early results are encouraging but questions remain around the long-term impacts of the one-off use of both mouldboard ploughs and rotary spaders. For example, there is a considerable risk of wind erosion, especially when the soil is dry. Additionally, researchers do not yet know the fate of the buried water repellent topsoil over time and whether it remains repellent, which will affect soil management in subsequent years.

“There is strong support from growers to continue researching buried water repellent soils over time and the trial at Badgingarra provides a good opportunity to assess this,” Dr Davies said.

A 2009 ‘straw-poll’ survey of 51 growers in the Mingenew area revealed that 98% would be willing to use inversion tillage to manage soil repellence and herbicide resistance weeds, once the technique had been proven.

Acknowledgements

This research was funded by GRDC through the Managing Hostile Subsoil Research project (UWA00081). GRDC is funding ongoing work through the new Delivering agronomic strategies for water-repellent soils in WA project (DAW00204), which started during July 2010.

Contact:

Dr Stephen Davies

Phone: (08) 9956 8515

Email: stephen.davies@agric.wa.gov.au