New trial findings are optimising the 'nuts and bolts' performance of deep ripping operations on sandy-textured soils in South Australia's low-rainfall cropping regions.
South Australian Research and Development Institute (SARDI) research agronomist Brian Dzoma says new knowledge drawn from two years of trial data has helped finetune important components of amelioration on compacted sandy soils.
These operational components, known to influence the effectiveness and cost-benefits of deep ripping operations, include tyne spacings and working depth.
Mr Dzoma, who is part of the regional research agronomist network supported by a GRDC-SARDI partnership, discussed the findings of the study at the 2020 GRDC Grains Research Update in Adelaide, South Australia.
He says SA trials during 2018 and 2019 highlighted the cost-benefits of using wide tyne spacings, instead of narrow spacings, for deep ripping operations.
These trials examined tyne spacing impacts on crop productivity on compacted sandy soils at Peebinga, in the Murray Mallee region, and at Buckleboo, on the Upper Eyre Peninsula.
The trials found deep ripping with either narrow (30 centimetre) or wide (60cm) tyne spacings achieved similar yield responses, despite the dry seasonal conditions in 2018 and 2019.
Based on this finding, Mr Dzoma urges growers to consider using wider tyne spacings since they can help reduce the operational costs of deep ripping compared with narrow tyne spacings.
"Ripping with narrow 30cm tyne spacings or wide 60cm tyne spacings gave similar outcomes in terms of overcoming compaction, promoting root growth and subsequent grain yield responses," Mr Dzoma says.
"Therefore, wider tyne spacings of 50 to 60cm, which require less fuel, horsepower and machinery maintenance, are preferable.
"Another advantage of wider tyne spacings is that there is potential to leave more standing stubble in the inter-row.
"This reduces the risk of wind erosion after ripping, especially in dry seasons."
The trials at Peebinga and Buckleboo looking at the impacts of ripping depth on crop productivity and the longevity of amelioration benefits also showed ripping is "most effective" where the tynes penetrate beyond the main compacted soil layer.
Where this approach is used on compacted deep sandy-textured soils, grain yield increases usually persist for at least two or three years, Mr Dzoma says.
"However, if the soil in or below the compacted layer is limited by other constraints, such as acidity, sodicity or salinity, the benefits of deep ripping may not be fully realised.
"This reinforces the importance of testing the soil at depth and understanding what factors might be limiting root growth before commencing a deep ripping program."
Another finding from the trials is that yield gains tended to improve with increased ripping depth.
The yield improvements linked to increased ripping depth were observed at three SA trial sites at Peebinga, Buckleboo and Loxton, in the northern Mallee region.
For instance, cumulative yield gains for the trials, measured in the 2018 and 2019 seasons, showed that the deepest ripping treatment, to a soil depth of 70cm, achieved the highest yield increases, compared with ripping at soil depths of 20cm, 40cm and 60cm.
Mr Dzoma attributes this yield gain to "increased root growth providing increased access to water and nutrients" at depth within the soil profile at the trial sites.
For example, the trial findings, averaged over two seasons at Peebinga and Buckleboo, saw a yield increase of 1.3 tonnes per hectare in wheat and 1.8t/ha in barley where the soil was ripped to a depth of 60 to 70cm, compared with ripping to a soil depth of 20cm.
"However, it is important to note that the highest-yielding treatment with the deepest ripping does not necessarily translate into being the most profitable and sustainable tillage strategy because of the extra fuel and machinery costs," he says.
"Careful diagnosis of sandy soil compaction and crop root development is required, particularly at depth in the soil profile, to inform a cost-effective approach to the depth of amelioration.
"The optimum depth of ripping will depend upon the depth of the compaction, and other underlying subsoil constraints.
"There is no point ripping to 70cm if the compacted layer is between 20 and 30cm, and subsoil conditions below the compaction are hostile to crop root growth."
The research team used a cone penetrometer to provide a measure of soil strength, known as soil penetration resistance (PR), to gauge soil compaction and the constraint it poses to root growth as part of the study.
"Growers are encouraged to use steel 'push-rods' as an alternative on-farm tool to determine the depth and extent of soil compaction in paddocks," Mr Dzoma says.
Sandy soils are generally considered compacted where PR exceeds 2500 kilopascals (kPA), which is known to restrict plant root growth and limit crop yield potential.
'Haying off' risk
Mr Dzoma says the SA trials also showed occasions where deep ripping has the potential to cause 'haying off' in seasons with a dry spring.
This is because deep ripping can stimulate early growth of vegetative crop biomass, which rapidly depletes the soil moisture profile, meaning there is inadequate stored soil moisture for grain filling, particularly in seasons with a dry finish.
"This ongoing research is showing that deep ripping is not always the complete solution," he says.
"A holistic approach, tackling more than just one subsoil constraint, can help improve the longevity of deep-ripping benefits and the overall return on investment.
"The responses to deep ripping in the SA trials will be re-examined during 2020, which is the third year after treatment, and economic trade-offs will also be estimated."
Note: SARDI is a division of Primary Industries and Regions South Australia (PIRSA).