Perils of ripping on sandy soils- what can be learnt from hindsight?

Take home messages

• Know what problem you are trying to solve with ripping.
• Year 1 benefits averaged 0.6t/ha but predicting the longevity of the ripping effect is not easy.
• Managing the seedbed on ripped soils requires special attention.

Background

Poor productivity is commonly reported for the deep sands that make up the cropping soils in the low rainfall Mallee regions of South Australia and Victoria. There is evidence of unused soil water with varying evidence of constraints commonly associated with sandy soils such as compaction, non-wetting, poor fertility or acidity. There is considerable interest in strategic deep tillage with/without agronomic amendments aimed at overcoming physical constraints and increasing water and nutrient supply within the soil profile. Strategic deep tillage includes ripping or deep ploughing (i.e. spading, plozza plowing, inversion) to depths of 30cm and more. Replicated trials including various combinations of these treatments have been established across the South Australian and Victorian Mallee. These trials are part of the research and validation work within the GRDC project; ‘Increasing production on sandy soils in the low-medium rainfall areas of the southern region’ (CSP00203). Although the benefits of deep ripping in deep sandy soils have been recognised previously, there is a need to understand where ripping can most reliably lead to yield benefits, how benefits can be maximised over multiple seasons, and which sands likely to respond. There are opportunities to improve the seedbed condition following ripping and this is being explored in a SAGIT funded project. Combining knowledge on where gains from ripping will come from and how to best manage the seedbed after ripping will help overcome the ‘perils of ripping sandy soils’.

Key question 1 - what is the problem I want to solve with ripping?

The main goal of ripping is to deal with soil compaction or a high penetration resistance. By breaking up the compaction, roots can penetrate deeper and make use of previously unused water. A secondary outcome of ripping is that some unused nutrients (either deep or not mineralised) can become available to the crop. However, with increased crop water use and yield, crop demand for nitrogen will also increase.

If the paddock has repellence that consistently limits crop establishment, then that needs to be the focus of the treatment that is implemented. While deep ripping can improve water infiltration, it will have limited effect on the amount of water repellency. If a disruptive tillage pass is made, and water repellency is not treated, then the vulnerability to erosion is going to increase and will need to be managed.

Key question 2 - what benefit will I get and how long will it last?

While a positive response to ripping in the first year appears to be quite reliable, with an average benefit of 0.6t/ha (Figure 1), predicting the yield effects in subsequent years has proven more difficult and has provided varied results from -0.3t/ha to +0.6t/ha.

Figure 1. Ripping (where 30= 30 cm deep, 60= 60 cm deep, Inc= inclusion plates at 60 cm deep) and spading yield benefits from Sandy Soils Project Experiments in the year of ripping.

Key question 3 - how do I manage the seedbed on ripped soils?

Paddock trafficability post ripping is a major constraint to the implementation of deep ripping on a commercial scale. Seeding and spraying operations are particularly affected which can lead to problems such as poor establishment, machinery damage and in some circumstances, soil erosion. A new experiment has been established at Pinnaroo in 2020 to investigate solutions to these problems. The experiment is measuring the effect of ripper type (Hanton and Sharrad ripper fitted with straight shanked Tilco tine and a Williamson Agri ripper fitter with curved Michel tines) and rolling on trafficability, seed depth and crop establishment. The trial was sown commercially by the collaborating farmer using a Horwood Bagshaw PSS system.

To simulate what’s likely in a grower situation, the trafficability following ripping was measured by driving a Landcruiser ute across the surface immediately prior to seeding and then measuring the depth of the ruts left by the tyres. Un-ripped treatments had shallow ruts of 40-50 mm but were 120mm in depth following deep ripping with both ripper types. Consolidating the ripped surface with a roller reduced rut depth by 50%. The rut depth data correlated with seeding depth data with wheat seeds from un-ripped and ripped and rolled treatments emerging from 20-30 mm depth while unconsolidated ripped treatments emerged from 50mm for the curved Michel tine and 60mm for the Tilco straight tine. The position of the seeding tine on the bar also affected the seed depth. As the seeder sinks in, soil throw from rear tines can bury seed placed by the front tines and the soil throw may also carry pre-emergent herbicides into the seed row. Seeds were germinating from 75mm depth from the front tine position but only from 45mm when sown with a back tine. This effect resulted in a 16% decrease in wheat establishment and reduced early vigour of the deep sown rows.

There are other pitfalls to watch out for when it comes to trafficability and establishment, including increased risk of damage from pre-emergent herbicides and slumping of furrows which also increased seed depth.

Growers and researchers are trying to improve the seedbed following ripping using a range of options including; press wheel design, ripping at an angle to seeding direction, and implementing a controlled or semi-controlled traffic situation where important wheel tracks are left un-ripped. Different seeding bar setups influence how successful seeding is in deep ripped paddocks.

Acknowledgements

The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC and SAGIT. The authors would like to thank them for their continued support.

Contact details

Therese McBeath
Locked Bag 2, Glen Osmond, SA, 5064
0422500449
therese.mcbeath@csiro.au