Paddock Practices: Tips and tools for planning management of soil constraints in 2019
Author: GRDC media | Date: 01 Feb 2019
Key points: Soil Constraints West project (2014-19)
- Major GRDC initiative for western region
- Multi-organisation collaboration
- Total project value $33 million
- Addressing solutions to key soil constraints - acidity, compaction, water repellence, deep subsoil issues (including sodicity)
- Researching soil biology and soil amelioration tactics
- Assessing effects on crop water use efficiency, nutrition, seeding/tillage systems, weeds and abiotic stresses
- New $42 million soils-focused partnership between GRDC and DPIRD will build on the Soils Constraint West research.
Introduction
Addressing soil constraints has potential to boost cropping returns by $100 per hectare or more across the WA grainbelt from increases in plant water and nutrient use efficiency and grain yields.
To help achieve this, a suite of research trial results, resources and tools stemming from the five-year Soil Constraints West project is now available.
These will be valuable when making 2019 budgeting and investment decisions about the most efficient and economic soil amelioration tactics to adopt for treating targeted areas of the farm.
GRDC initiated the $33 million Soil Constraints West project in 2014 and research trials have since been carried out across multiple seasons for all major WA soil types. This has been done in collaboration with research agencies, grower and industry groups, advisers and individual growers.
Research has focused on the most common constraints of soil acidity, compaction, water repellence and subsoil issues (including sodicity) and investigated the best and most cost-effective amelioration tactics to tackle these.
Impact on crop water use efficiency, nutrition, seeding/tillage systems, weeds and abiotic stresses have been considered.
Key findings from the Soil Constraints West initiative highlight the major economic, production and sustainability benefits possible when soil limitations are overcome. These are outlined in new GRDC podcasts that can be accessed here and videos available here.
A new $42 million soils-focused partnership between GRDC and DPIRD will build on the Soil Constraints West research. More information about the recently announced partnership, comprising three new soils research projects, can be found here.
WA grower actions stemming from Soil Constraints West
In the five years of this initiative in WA there has been:
- A big increase in lime use and its subsoil incorporation to address acidity
- More deep ripping to help overcome compaction
- Extensive assessment and adoption of a range of strategic deep tillage and soil inversion systems
- Adoption of a range of deep ripping systems
- Adoption of soil wetters on responsive soil types, particularly water repellent forest gravels.
WA growers are also recognising the benefits of shifting to controlled traffic farming (CTF) systems to ensure longevity of results.
A brief overview of some of the common soil constraints and tactics being successfully trialled and used by researchers and grain growers to address these is outlined below.
Importance of soil testing to depth
Soil testing to depth helps identify the constraints affecting crop production and where the biggest ‘bang for buck’ can be achieved from ameliorating these.
It is best to test to a depth of at least 30 centimetres - and often to 50cm - in 10cm increments and include pH in the analysis.
It is then typically best and most economic to target treatments to the constrained areas and zones on the farm with the highest potential for crop production.
An overview of diagnosing soil acidity and guidelines for soil testing can be found here.
Common soil constraints and tactics for management
Across the WA grainbelt, soils typically have multiple constraints impeding crop root growth and productivity.
Short and long-term returns from overcoming constraints are optimised when they are correctly identified and managed at an individual paddock or farm zone level. That is a key take-home message from the Soil Constraints West initiative, according to Department of Primary Industries and Regional Development (DPIRD) Soil Science and Crop Nutrition manager Chris Gazey.
Soil acidity
Mr Gazey says, despite widespread liming programs, about 70 per cent of WA’s agricultural topsoils (in the 0-10cm layer) and almost half of subsurface soils (in the 10-20cm and 20-30cm layers) have pH (measured in CaCl²) below the recommended levels of 5.5 (surface) and 4.8 (subsurface).
The most effective way to address this is deep soil sampling and treatment with lime that is incorporated to depth.
Through the Soils Constraints West project, research has included investigating the best lime sources, particle size, interactions with gypsum and incorporation methods. Some key findings and management tactics can be in the update paper '20 Years of soil acidity RD and E in WA'.
Soil compaction
Subsoil compaction has increased in severity and depth in recent years, especially in deeper sandplain soils where it is more critical for plants to be able to extract water and nitrogen from deep reserves to reach yield potential.
Research through the Soil Constraints West project has found deep ripping these soils can boost wheat yields by up to 35 per cent, with the best gains coming from deeper treatments.
A GRDC-invested project in 2016 and 2017, led by Bindi Isbister, of DPIRD, and Craig Topham, of Agrarian Management, showed deep ripping to 50-60cm could lift cereal and canola yields by 21-66 per cent across a range of soil types and rainfall zones in the Geraldton port zone.
Ripping to a depth of 30cm increased yields by 6-24 per cent compared to no ripping.
Economic analysis as part of this project found the higher cost of deeper ripping provided a positive return on investment of up to $5/ha for every dollar invested at three sandy sites, but not on a red loam.
The loam had a negative return on investment of $0.63/ha for every dollar invested. On a sandy soil at Ogilvie there was a yield penalty in lupins in 2016, resulting in a negative return on investment which could not be recouped in the following dry season of 2017.
Bindi says this signals a warning to plan rotations well, as lupins tend to pose a higher risk if planted in the first year after ripping below 40cm.
More results from the sites treated with deep ripping as part of this project can be found in the trial report 'Deep ripping, deeper deep ripping and water use efficiency' and information about deep ripping can be found in the article 'Deep ripping for soil compaction'.
Research in some areas of WA has found newer topsoil slotting (or deep placement) technologies can lead to yield gains of up to 53 per cent in the initial year of ripping.
These methods mechanically incorporate narrow strips of lime - or lime amended topsoil - into the acidic subsoil horizon to mitigate acidic pH-induced subsoil Al toxicity and associated crop yield loss.
Typically, this involves deep ripping with ‘inclusion plates’ placed behind the tynes to a depth of 30-50cm to loosen compaction layers and achieve topsoil ‘slotting’ behind the tyne.
Longer-term impacts of topsoil slotting are still being assessed, but appear to vary with soil type and conditions at the time of ripping. Also, see a video of topsoil slotting in action.
Topsoil water repellence
These types of soils have uneven water infiltration, leading to poor crop and pasture establishment, difficulties in weed control and lower water and nutrient use efficiency.
The result is poorer productivity, exacerbated herbicide resistance issues and more exposure to erosion.
Tactics to address water repellence include using furrow sowing, no-tillage seeding systems, soil wetters, clay, lime, on-row sowing, deep soil mixing or soil inversion.
Soil mixing and inversion tactics can be especially effective treatments and lift crop yields by burying topsoil and bringing more ‘wettable’ soil to the surface. This helps rainfall to infiltrate the soil profile.
Through Soils Constraints West, GRDC is investing in research to further understand the fundamental science and management of WA’s water repellent soils.
PhD students are helping to assess molecular chemistry of water repellence in soils, with this understanding having potential to develop more targeted chemical or soil wetter treatments.
They are also studying the environmental effects of rain, humidity, temperature on expression of soil water repellence.
Several options are available to help manage soil water repellence and have been the subject of research in the Soil Constraints West initiative. Some key findings include:
More information about water repellent soils and management options is available on the 'Water repellence' resource page on the Department of Primary Industries and Regional Development website.
Managing multiple constraints
Many WA soils have a combination of surface water repellence and subsurface compaction and acidity.
A range of soil amendments, with various forms of strategic deep tillage, can address multiple constraints and provide larger and more prolonged benefits. These can last for a decade or more.
The impact of a range of strategic deep tillage tactics at several central grainbelt sites and soil types has been investigated by DPIRD research officer Dr Stephen Davies and shown significant grain yield increases are possible.
Some key findings from his research include:
- Pale deep sands
- average 26-50 per cent higher yields in year one
- deep ripper or one-way plough are the most cost-effective treatments.
- Deep sand over gravel
- yield increases of 2-93 per cent in year one after deep ripping
- one-way ploughing was most profitable in short-term due to lower cost
- deep ripping with spading, and soil inversion (using a mouldboard plough) are showing better long-term benefits and profitability than ripping alone on soil with higher yield potential.
- Removing subsoil compaction and topsoil repellence is critical
- Deeper soil mixing is important.
Dr Davies says optimal cost-efficiency is achieved by understanding the constraints, benefits and expected longevity of amelioration treatments for specific soil types.
When choosing a strategic deep tillage tactic, he advises growers to:
- Soil test to depth to understand constraints
- Apply lime and incorporate it to depth if needed
- Prepare paddocks well - remove rocks brought to surface, fill-in furrows and level paddock, potentially roll the paddock for a firm seed bed
- Use a method compatible with seeding equipment
- Use CTF to prolong the benefits and minimise re-compaction.
Dr Davies says multiple tactics are generally needed to address multiple constraints and - across much of WA - a winning strategy is a combination of lime or other soil amendment application with incorporation, subsequent deeper ripping and use of controlled traffic, especially for sandy soils.
But he says investments should be weighed up against paddock yield potential.
Lime, gypsum and incorporation
Latest results from DPIRD trials led by soil scientist Dr Gaus Azam, with GRDC investment, show wheat yields can be significantly increased on acidic sandplain soils when lime and gypsum are incorporated to depth with cultivation.
At a Kalannie site, using a one-way pass from a plough or rotary spader improved soil pH well above the recommended level of 4.8 at a depth of up to 20cm, which eliminated aluminium toxicity.
Dr Azam says this led to an extra 26 per cent (0.25 tonnes/hectare) in average wheat yields in the low yielding season of 2017 where the tillage removed compaction and lime and gypsum were mixed, compared to control areas where only deep tillage was used to remove compaction. There was an extra 0.4t/ha yield advantage in 2018 as well.
Plots with application of lime only had a 14 per cent yield benefit, while gypsum only had a yield response of 4 per cent.
Dr Azam says the trial highlights the importance of incorporating lime using cost-effective strategic tillage to recover acidified soil profiles in the most economic way. DPIRD is continuing work to understand the interaction with gypsum and where it is applicable.
Tools and resources to aid soil amelioration decision-making
Ranking options for soil amelioration (ROSA) model
Through Soil Constraints West, and with GRDC investment, DPIRD has developed the ROSA model. This compares the economics of adopting one or more of the most common soil amelioration tactics used in WA for all major soil types.
It includes options for mitigating acidity, water repellence, compaction and soil structure decline and ranks likely cost:benefit scenarios for using claying, deep ripping, gypsum, lime, deep soil mixing and/or wetting agents.
Costs and returns are calculated on a short and long-term basis.
DPIRD economist Dr Elizabeth Petersen outlines how growers can use ROSA in a GRDC podcast that can be found here and more information, including how to access the ROSA model, is available in this previous Paddock Practices article.
CTF and the CTF calculator
CTF is a long-term management strategy that can help minimise the effect of soil compaction on crop production.
The aim of using this system is to minimise trafficked areas of paddocks as much as possible. A common target, using a fully-matched system, is to have traffic wheels covering only 9-12 percent of the total paddock area (compared to 40 per cent in a standard no-till system).
The CTF calculator, developed as part of the Soil Constraints West project with GRDC investment, can estimate the percentage of a paddock currently trafficked. It then analyses costs:benefits of a range of management options for overcoming compaction, including CTF combined with deep tillage and changing machinery specifications.
Get started with the CTF calculator at http://ctfcalculator.org/.
Lime Profit Calculator
A Lime Profit Calculator, developed as part of a Liebe Group and Farmanco project with GRDC and DPIRD investment, assesses:
- Amount of lime required to change pH
- Cashflow and profit of a range of liming programs across 10 years
- Payback period
- Initial rate of return
- Net present value.
The Lime Profit Calculator can be accessed here.
During 2019, GRDC is investing in the development of a new mobile telephone App-based lime calculator as part of a suite of new smart technologies through the Soil Constraints West initiative.
More information
Chris Gazey, DPIRD, 08 9690 2000, 0429 107 976, chris.gazey@dpird.wa.gov.au
Dr Stephen Davies, DPIRD, 08 9956 8515, 0408 439 497, stephen.davies@dpird.wa.gov.au
Useful resources
Soil Constraints West information on the GRDC website
Soil quality ebook ‘Soil Quality: 1 Constraints to Plant Production’
Soil quality ebook ‘Soil Quality: 2 Integrated soil management'
GRDC podcasts
GRDC videos
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