Take home messages

• Inclusion ripping technology is designed to drop topsoil deep into the rip-line during the process of subsoil tillage.
• Adding inclusion plates to a deep ripper substantially increases the draught requirement, but this may be minimised by using improved ripper point and plate combinations.
• The depth of the plate bottom edge has the greatest impact on the draught force.
• The plate design and settings, ripping speed, timing of operation, soil type and moisture are key factors driving the inclusion performance.
• High ripping speed greatly reduces the amount of topsoil inclusion, but this can be mitigated by increasing the length of the plate.
• The operating depth of the top edge of the plate relative to the soil surface determines the thickness of topsoil layer being included, but the impact of soil upheaval while ripping needs to be factored in.
• Computer simulation is a powerful tool to help optimise solutions for passive inclusion and ultimately, for more selective active inclusion systems.

Background

Topsoil inclusion is an enhancement of deep ripping, pioneered as ‘topsoil slotting’ in Western Australia in the early-mid 2010s (Parker, 2017). To enable topsoil inclusion, a braced pair of flat plates are bolted behind a deep ripping tyne and spaced to form side-shields. During deep ripping in sandy soils, the cavity forced open by the tyne is expanded by the plates, which allows quantities of loose and flowable topsoil to naturally fall over their upper edges deep within the loosened soil profile.

The use of inclusion plates aims to create a column of improved soil down the profile into subsoil that has been previously constrained by limitations to root growth, for example high soil strength, poor structure (dispersion), nutrient deficiencies, acidity or alkalinity. Inclusion ripping often results in additional crop biomass and grain yield when compared with deep ripping alone, and with longer-lasting benefits as suggested in recent research (McBeath et al. 2022). This is particularly the case in stratified sandy soils when the topsoil is rich in organic matter, mineral nutrients and/or amendments (for example, lime or manure). Inclusion of these topsoils improves depleted sublayers, the growth of deep roots and uptake of moisture and nutrients.

Inclusion ripping has faced some dis-adoption in the West due to variable crop responses and implementation challenges. Supported by GRDC funding, research at UniSA has investigated the impact of plate design and operational settings on the quantity of topsoil material included at depth, both behind commercial inclusion plates and behind novel proof of concept high-capacity plates.

Method

Alongside field work carried out to visualise and assess the amount of topsoil included during the inclusion ripping process, the Discrete Element Method (DEM) computer simulation approach was used to develop a better understanding of the top layer inclusion process and, also, how to optimise it. The DEM simulation can track and visualise soil particle movement and provide an accurate basis to quantify final topsoil inclusion outcomes.

During inclusion ripping, the backfilling process happens naturally, starting with the soil directly above the upper edge of the plates falling over the edge, followed by layers above it, into the cavity. This passive inclusion process is controlled by factors such as forward speed, plate position below the surface, plate side wall length, as well as overall flowability of the soil affected by moisture and residue content. The standard parameters of a narrow shank ripper tyne and its inclusion plate geometry can be seen in Figure 1.

Figure 1. Standard parameters of ripper tyne and inclusion plate geometry.

To investigate the process and what effects the plate geometry has on inclusion performance, a standard commercial inclusion plate was used as a baseline, both in field trials and in the computer simulation. The impacts of plate length, upper-edge depth and under-plate clearance on inclusion performance have been investigated via computer DEM simulations (Ucgul et al. 2019) and were validated in the SA Mallee during 2019.

Results and discussion

A typical inclusion outcome can be seen in Figure 2, showing a rear view of the undisturbed profile on the left and the result of an inclusion plate passing on the right. The dotted line represents the depth of the inclusion plate in the soil profile (150mm below the surface). It can be seen how the inclusion space is filled with particles from various layers from above the plate edge, with the layers at the height of the top edge when the plate passes, ending up at the bottom of the cavity. This shows that the included soil also contains soil layers initially located below the top edge of the plate (for example, lighter colour in Figure 2), but brought up from the upheaval associated with soil loosening by the ripping tyne. A 150–200mm vertical upheave of soil and an outward rotation is typically observed in the field during the deep ripping process.

Figure 2. Typical inclusion outcome of passive backfilling.

The gradational mix of soil within the inclusion space suggests that inclusion occurs mainly as a ‘full layer collapse’ over the plate edge and not as a ‘surface-first’ shedding process, which is consistent with paddock observations. When comparing the inclusion of a range of plates, reduced speed and increased side wall length are most influential in maximising the amount of topsoil included to depth.

Figure 3. Burial performance of a standard commercial inclusion plate at 7km/h.

Figure 4. Burial performance of a high capacity inclusion plate at 7km/h.

The comparison of a standard 250mm long commercial inclusion plate and a 600mm long high capacity plate can be seen in Figure 3 and Figure 4. Both these plates were 131mm wide, 390mm high and operated at 600mm deep and at 7km/h, and the top edge was set to 150mm below the original soil surface. These graphs show for each 50mm thick zone of inclusion down the profile, the proportion of four original layers present, while the top 0–150mm is often a key layer of interest for inclusion. As seen in Figure 4, increasing the side wall length increased the amount of (darker colour) 0–150mm top layer burial at depth and also the layers that are heaved above the plate during the ripping process (shown in white on the graphs).

Figure 5. Burial performance of a high capacity inclusion plate at 4km/h.

The same high capacity plate was compared over a range of operating speeds (Figures 4 – 6). When the speed of operation was reduced from 7km/h to 4km/h, there was a large increase in the amount of 0–150mm topsoil reaching full depth of the inclusion plate. When the speed was further reduced down to 2km/h, over 65% of the topsoil occupied much of the cavity down to ripping depth.

Figure 6. Burial performance of a high capacity inclusion plate at 2km/h.

By increasing the length from 600mm to 1090mm and the depth from 390mm to 490mm, the speed could be increased back to 4km/h, whilst still increasing the amount of topsoil inclusion (Figure 7). A lack of topsoil in the 150–250mm layers can now be seen, meaning that there was insufficient material to completely fill the cavity and some assistance is needed.

Figure 7. Burial performance of a longer, high capacity inclusion plate at 4km/h.

Maximising inclusion capacity

The above work shows that topsoil inclusion capacity can be improved greatly by using (much) longer plates operated at (much) lower ripping speeds. This, however, may not be practical enough to support widespread adoption, and pilot work was initiated during 2020–21 to investigate more active inclusion systems of backfilling, positively forcing topsoil material into the cavity using helping tools. Figure 8 shows a proof-of concept embodiment featuring backfilling discs, mounding discs and a levelling consolidating roller combined with 600mm long inclusion plates. Limited field testing was conducted on the Yorke Peninsula in 2020 and a trial was initiated at Lowaldie in 2022 as part of a strip inclusion ripping treatment.

Figure 8. Active inclusion system can maximise capacity without compromising on work rate.

Conclusion

Field testing and DEM computer simulations show that the performance of inclusion plates varies widely and is affected by key factors, such as the speed of operation and the side wall length of the inclusion plate. Increasing the side wall length can compensate for the negative effect of greater forward speed, but there are practical limitations to maximum plate lengths. The top edge height of the inclusion plate acts to target the layers of interest, taking into account the soil upheave expected during ripping. Reducing operational speed down to 2km/h, while impractical, is most effective at maximising inclusion capacity, and highlights the potential for much better performance of topsoil inclusion. Component-assisted or active inclusion has the potential to match that level of performance without the need for excessively slow speeds, but more research work is required in this area.

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, the author would like to thank them for their continued support. Special thanks to Ryan and Shannon Hewett of Bute and Peter Lowlier of Lowaldie.

References

Ucgul M, Saunders C, Desbiolles J (2019) Simulations into strategic tillage implement performance. GRDC GroundCover™, Soil Constraints Part 1, November-December 2019.

Parker W (2017). Decreasing subsoil constraints with topsoil slotting plates. Proceedings of the 18th Australian Society of Agronomy Conference, 24–28 September 2017, Ballarat, Australia.

McBeath T, Llewellyn R, Azeem M, Ouzman J, Macdonald L, Moodie M, Desbiolles J, Saunders C, Trengove S, Wilhelm N, Fraser M, Whitworth R, Unkovich M, Mustafa, da Silva R (2022) Ameliorating sandy soils to overcome soil constraints and improve profit. GRDC Update paper.

Inclusion ripping technology: National

Ripping technology: National

Blackwell P, Isbister B, Riethmuller G, Barrett-Lennard E, Hall D, Lemon J, Hagan J, Ward P (2016)Deeper ripping and topsoil slotting for more profitable management of subsoil. GRDC Update paper.

Contact details

Chris Saunders
University of SA
Mawson Lakes, SA 5095
8302 3664
chris.saunders@unisa.edu.au
@AgEngUniSA