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.

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.

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.

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.

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.

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:

• Banded soil wetters are reliable, especially for improving yields on repellent forest gravel soils of south west WA - and when dry sowing
• Strategic deep tillage involving deep soil mixing or inversion can effectively overcome soil water repellence, and other constraints, and increase grain yields for an extended period
• Effective strategic deep tillage can help crops in dry seasons and periods of climate stress
• Clay delving and clay spreading with deep incorporation can further reduce repellence and, in some cases, help maintain a longer benefit.

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.

GRDC Research Codes:
DAW00242; DAW00243; DAW00244; AVP00003-A; DAW00252; DAW00236; LIE0006

Contact:
Chris Gazey, DPIRD
08 9690 2000, 0429 107 976
chris.gazey@dpird.wa.gov.au

Dr Stephen Davies, DPIRD
08 99 56 8515, 0408 439 497
stephen.davies@dpird.wa.gov.au

Useful resources:
Soil Constraints West information on the GRDC website: https://bit.ly/2GMOHcx
GRDC Soil quality ebook ‘Soil Quality: 1 Constraints to Plant Production':
https://apple.co/2tFWEY6
GRDC Soil quality ebook ‘Soil Quality: 2 Integrated soil management':
https://apple.co/2EV4q4n
GRDC podcasts: https://bit.ly/2VqGmyh
GRDC videos: https://bit.ly/2H4WjGx