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Key messages

• Deep ripping to the depth of the hardpan in yellow sand, sand-over-gravel duplex soils and gritty grey clay generated positive yield responses for up to four years when paddocks were managed under a controlled traffic farming system.
• There was no benefit to deep ripping a calcareous loamy earth.
• Deep ripping in a controlled traffic farming system generated an accumulated return on investment of $1-29/ha over four years depending on depth or the addition of topsoil slotting plates.

Aims

Seven trials were implemented in 2015 with the primary aim of evaluating the financial viability of new deep-ripping methods. It was hypothesised that the financial return from ripping would be increased by ripping to a greater depth using topsoil slotting and implementing a controlled traffic farming (CTF) system to improve longevity of the ripping effect on root growth and crop yield.

Introduction

With increasing size and weight of machinery in the drive for efficiency and economy of scale comes decreased soil physical properties and fertility through subsoil compaction. Generally, as weight of machinery increases so too does the depth of subsoil compaction, dependent on contact pressure and weight distribution. In recent years there has been a realisation of this as crops failed during periods of heat stress or constraint-induced drought (Sharma 2017). Subsoil compaction reduces the ability of roots to penetrate soil, in turn reducing access to moisture and nutrients.

Deep ripping with tine implements is the most common way to alleviate subsoil compaction. As compaction becomes deeper the cost of alleviation also increases as larger, more expensive machinery is required, which uses more fuel and has greater machinery depreciation. For ripping to have maximum benefit the bottom of the tine must penetrate below the bottom of the hardpan. While ripping sandy soils to depths of 300-350mm has been standard practice since deep ripping was introduced, these shallow depths of ripping are no longer producing the required crop yield responses. Blackwell et al (2016) found root growth was still impeded by compaction even with ripping to 300-350mm, with plants having reduced access to moisture and suffering heat stress during grain fill. Considering these findings, growers are needing to understand their new depth of hardpan and invest in ripping that extends beyond the standard practice of 300-350 mm.

It is rare that soils suffer only single constraints with several issues more often present that reduce crop production. Water repellence, low subsoil pH and inherent sodicity are found in combination with subsoil compaction at variable concentrations dependent on soil type (Davies et al 2019). Mouldboard ploughing, spading and disc ploughing are used to reduce water repellence and these practices can all move lime through a profile rapidly in one pass (Davies et al 2019). These aggressive amelioration methods come with the risk of erosion, poor crop establishment and creation of a hostile surface soil. Growers began investigating less aggressive means of incorporating topsoil ameliorants through burial during deep ripping. This was done using various attachments behind the ripping tine to encourage topsoil to fall in behind the tine. In combination with ripping below 400mm these attachments can move ameliorants into depths beyond those of the spader or mouldboard plough. Such incorporation allows alleviation of compaction and, to a lesser extent, deeper burial of lime with a reduced risk of erosion and creation of a hostile soil surface.

From these early investigations, a system involving topsoil slotting plates were developed. This involved a pair of trailing plates, separated by up to 130mm, attached to the rear of the ripping tine that opened up a slot in the soil as the tine moved through it. When working below the surface a volume of topsoil falls into the gap created by the plates. Organic matter or soil ameliorant applied to the soil surface are then mixed with the topsoil through a narrow channel to depth in the profile. These channels allow some plant roots to avoid areas of constraint by accessing moisture and nutrients deeper in the soil. In following years, additional ripping can be offset to open more channels. Topsoil slotting plates can provide some of the benefits of the more expensive amelioration treatments, such as mouldboard ploughing or spading, to soil types unsuited to these types of amelioration. In particular the low rainfall and high erosion risk areas of the wheatbelt.

We hypothesised that the financial return from ripping would be increased over ripping to 300 mm by ripping to a greater depth with topsoil slotting and then implementing a CTF system to improve longevity of the ripping effect on root growth and crop yield.

In this paper the term ‘deeper ripping’ is used to describe the deep ripping treatment that was greater than the standard ripping treatment of 300mm included at each site.

Method

The trials were implemented in 2015 using a custom-built shallow leading tine ripper 3.5m wide, with or without topsoil slotting plates on the following tines. Eight different soil types were selected at six sites throughout Western Australia (Table 1). A site with York Gum soil at Beacon was dropped due to weediness after the second season, so is not included in this paper. Soil type variability at Broomehill and the complex interpretation required of this site mean it is also excluded from this review. For a full method and description of ripping equipment used in 2015 see Parker et al (2017).

Table 1. Soil type, depth of ripping treatments, depth to hard pan at all seven sites and exchangeable sodium at two trial sites across Western Australia. TS = topsoil slotting plates.

The trial design replicated ripping treatments in complete blocks. Replicates varied from three to eight depending on the available space at each site. All deeper ripping treatments were done with and without topsoil slotting plates on the following tines. Sites were managed under a CTF system with no traffic on the treatments. Nil rip plots were used as a pre-rip soil strength comparison, data not presented.

A return on investment analysis was performed each season by comparing the yield of each treatment to the ‘nil rip’result. The cumulative return on investment was determined by summing the value of response from each season, taking the initial cost from this sum and dividing by the initial cost to give the return for every dollar invested are outlined in table 2. The grain price as received at Kwinana was used to determine the value of responses for each season, so no discounting was applied.

Table 2. Cost assumptions used to calculate the cumulative return on investment, from observations taken at the time of ripping.

Results

Return on investment

At Moora, deeper ripping and topsoil slotting of high-value canola in the first-year resulted in a large cumulative return on investment (ROI) in year four (Table 3). Topsoil slotting plates at Munglinup continued to provide a positive return in all four seasons while the 300mm and 600mm ripping began to decline in value at this site in year four. The only positive return at Beacon, where the subsoil is sodic, came from ripping with slotting plates.

Table 3. Cumulative return on investment return on investment from deeper ripping, with topsoil slotting (TS) for all sites except Broomehill*.

Conclusion

The project found deeper ripping to >400 mm (with or without topsoil slotting) and in combination with CTF produced a positive yield response in sand, loamy earth and gritty grey clay soil. Over four seasons the total return on investment was between $1-29 for every dollar invested at the time of ripping. These trials were done within a CTF system that confined compaction to consistent wheel tracks, minimising re-compaction and helping to protect soil physical fertility for up to four years.

Deeper ripping was required to manage the hardpan that was below 350-450mm. Shallow ripping of sandy soil at 300mm or less was insufficient to alleviate compaction for improvement of crop yield. The deeper ripping gave greater access to moisture deeper in the profile. Ripping deeper than 300mm was necessary to increase yield potential at Binnu and Moora and topsoil slotting plates were required at Munglinup to increase the potential of ripping.

Deeper ripping with slotting plates increased yield but cost more. As ripping depth increases draught force on the tractor increases. As draught force increases so too do fuel and maintenance costs. While the current design of slotting plates enables burial of topsoil, it increases draught force to the point where growers remove plates to maintain ripping depth. The returns to deep ripping with slotting plates can be improved by reducing draft caused by the plates. The project investigated ways to improve the design of the plates to increase topsoil burial and reduce draft. By lengthening the plate and increasing the plate height, topsoil burial was improved without major increases in draught force. These draught adjustments were not included in the financial analysis, Reduced draught force reduces the operational cost by reducing fuel use. Where draught reductions are able to reduce the cost of the operation then return on investment is increased. The project recommends that growers understand these improvements when investing in slotting plates to maximise the return of the slotting process.

Further investigation of the interactions of crop rotation after ripping is required. Crop choice in the season of deep ripping had a large influence on the return on investment. A large yield response combined with a high-value crop, such as canola, provided large return on investment in the first year. The trial at Moora is evidence of this where ripping returned up to $15/ha/dollar invested (Table 3) in year one when a high value crop was grown canola was grown. Careful management of crop establishment on deep ripped soil, along with herbicide and fertiliser requirements, could provide a greater return in the year of ripping. The timing of lupins in the rotation needs to be better understood. Losses occurred in Binnu when lupins were established in the second season after ripping, though monitoring indicated re-compaction had not occurred. The 1t/ha yield increase in year one meant more nutrients were exported from the topsoil slotting plots in grain than other plots, but this was not adjusted for in future years. It is possible that changes to fertiliser management could be required to maximise the benefit and longevity of the yield response in systems already under controlled traffic.

Deeper ripping was less reliable and resulted in a negative response in soils when high levels of exchangeable sodium were present in the sub-soil, such as at Beacon. In clayey, sodic soils there is often a sodium percentage gradient that increases with depth. A straight tine deep ripper will indiscriminately mix the gradient bringing high concentrations of sodium to the surface or mix it through the profile. At the Beacon site, ripping resulted in negative or no ROI. Return at Beacon was only positive where topsoil slotting plates were used, and not in the first year. Ripping sodic soils at Ongerup reduced returns when the depth of ripping was increased. The cost of ripping to a greater depth outweighed any yield benefit in year one. As with Beacon, deeper ripping at the Ongerup site brought sodic subsoil to the surface, which then contributed to cloddiness and reduced emergence throughout the trial decreasing ROI with deeper ripping. Other methods of amelioration, such as application of gypsum in the absence of ripping, might have provided financial returns.

Root counts carried out during the final year of observations showed improved root exploration deep in the profile from deeper ripping both with and without topsoil slotting plates on sandy soil. Topsoil slotting plates incorporated additional topsoil organic matter and aided mixing of surface-spread lime through the profile (Davies et al 2017). It was expected that root activity under slotting treatments would be greater than non-slotted treatments though this was not the case. In these trials, root numbers for deeper ripping with slotting plates did not significantly differ from the deeper ripping alone.

Controlled traffic, deep ripping and topsoil slotting plates are necessary features for future farming systems to maintain physical fertility and continued return on investment. As indicated in over five years of research the success of each amelioration method is dependent on soil type and physical and chemical properties. Traffic management will help maintain soil physical structure and access to nutrients in those soils not suited to ripping.

References

Blackwell P, Isbister B, Riethmuller G, Barrett-Lennard E, Hall D, Lemon J, Hagan J, Ward P, (2016) Deeper ripping and topsoil slotting to overcome subsoil compaction and other constraints more economically: way to go!, Proceedings GRDC Grains Research Updates 2016, available at http://www.giwa.org.au/2016researchupdates

Davies S, Parker W, Blackwell P, Isbister B, Betti G, Gazey C, Scanlan C (2017) Soil amelioration in Western Australia, Proceedings GRDC Grains Research Updates 2017, available at https://grdc.com.au/resources-and-publications/grdc-update-papers/tab-content/grdc-update-papers/2017/02/soil-amelioration-in-western-australia

Davies S, Armstrong R, Macdonald L, Condon J and Paterson E, (2019) Soil constraints: A role for strategic deep tillage in (Eds J Pratley and J Kirkegaard) Australian Agriculture in 2020 From conservation to automation pp 117-135, Agronomy Australia and Charles Sturt University: Wagga Wagga.

McDonald, R. C., Isbell, R., Speight, J. G., Walker, J., & Hopkins, M. (1998). Australian soil and land survey: field handbook. Clayton, Victoria: CSIRO publishing

Parker W, Isbister B, Hall D, McDonald G, Riethmuller G, Blackwell P. (2017) Longevity of deep ripping and topsoil inclusion in soils under traffic farming; evidence from the second season. Proceedings of GRDC Research Updates 2017, Crown, Burswood, Perth.

Sharma D, (2017) Guidelines for wheat yield loss. Agricultural Science, Vol 29, No. 1, pp 28-39.

Acknowledgments

The trials presented here are from DPIRD and GRDC project DAW00243 ‘Minimising the impact of compaction on crop yield in WA’. Thank you very much to Glenn Mcdonald, David Hall, Tom Edwards, Glen Riethmuller, Chad Reynolds and Jo Walker for assisting with trial management and data collection.

The project would like to acknowledge the work of Dr Paul Blackwell in beginning this work in 2014 and setting up the trials 2015.

The growers involved in the project for their time and effort during set up and annual management of each trial site, Piet Diepeveen, Lawson Grains, the Faulkner brothers, Scott Thompson, Wes Harding, thank you.

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.

Contact details

Wayne Parker
Department of Primary Industries and Regional Development
20 Gregory st Geraldton, 6530
08 9956 8511
wayne.parker@dpird.wa.gov.au

Appendix

Yield results, t/ha, from each site for the four seasons of trial observations. Broomehill, Beacon York Gum and Moora spaded results not presented in the preceding paper. * indicating significant yield response over the Nil for the respective season (p=0.1), TS topsoil slotting, s spading.