Discs and stubble aid non wetting soils

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Trials at Munglinup on Western Australia’s south coast show combined use of zero-till and stubble retention is up to twice as productive as cultivation and stubble removal on non-wetting soils.

This GRDC-funded research over four years was conducted by CSIRO, the Department of Agriculture and Food, Western Australia (DAFWA), and the Ravensthorpe Agricultural Initiative Network (RAIN).

CSIRO soil microbiologist Dr Margaret Roper says the trials support growers’ observations that zero-till and stubble retention eliminated the effects of water repellence on acidic, sandy soils in both wet and dry seasons.

Photo of blue dye seeping into soil

Entry of blue dye solution
into soil immediately
following cultivation at
Munglinup in WA’s
south-coast district.

Photo of blue dye seeping into soil

Entry of blue dye solution
into soil under zero-tillage
at Munglinup in WA’s
south-coast district.

Dr Roper says the trials indicate that the yield gains zero-tillage and stubble retention provid in canola, barley and wheat result from improved water infiltration in the soil.

“Under zero-tillage, bio-pores formed by roots and organisms in the soil are preserved and provide pathways for water movement,” Dr Roper says.

“This is supported by our observations of water infiltration in the soil using blue dye solutions.

“After a crop is harvested the pathways created by its root systems and organisms continue to conduct water into the soil,” she says.

Although the research examined a zero-till farming system, Dr Roper says the findings are likely to be similar in minimum and no-till systems, even though there is slightly more soil disturbance where knife points are used for seeding instead of discs.

“In our experiments, crops were seeded with discs on the previous year’s inter-row, which resulted in no disturbance of remnant root systems from the previous year,” Dr Roper says, adding that using this approach with knife points is also unlikely to disturb remnant root systems.

She says the trial results also raise the question of whether it is more beneficial to sow on or close to crop rows from the previous year, to help crops access water that dead roots have channelled down the soil profile.

“In choosing which approach to take, growers should consider how much their seeding practices disturb the soil,” she says. This could help avoid breaking the continuity of root channels while sowing as close as possible to crop rows.

Dr Roper says the research further shows that retaining stubble instead of burning it usually increases yields. 

She says standing stubble may provide a conduit for water infiltration and reduce soil water evaporation, but it could also reduce temperatures in the upper soil layers.

“This means water-repellent waxes might be less likely to be deposited onto the surface of soil particles.”

She says while some growers in WA’s northern grain-growing region have been using spading or mouldboard ploughing to help ameliorate non-wetting soils, many growers further south were reluctant to use these techniques.

“Many soils in WA’s southern cropping areas have an extensive gravel layer below the soil surface, so spading or mouldboard ploughing may pose difficulties,” Dr Roper says.

“These growers are also nervous about the potential for soil erosion. “In the past four years, we’ve seen two major erosion events that completely lifted the soil surface.”

GRDC-funded trials looking at non-wetting soils are also being conducted on the Eyre Peninsula, South Australia.

More information:

Dr Margaret Roper
08 9333 6668

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GRDC Project Code CSP00139, CSP00117

Region South, West, North