Soil Amelioration & Groundcover Post-Harvest: Implications for Farmers

By Kate Parker, WMG Project Officer

Introduction

The months between harvest and seeding are a critical period for maintaining soil health, protecting productivity, and enhancing environmental resilience. Groundcover during this time plays a vital role in reducing erosion, improving soil moisture retention, and sustaining long-term soil function.

As part of a 2024 trial conducted on Tim Creagh’s gravel soil paddock in Dandaragan, funded by GRDC through the Soil Water Repellence Project, WMG observed significant differences in post-harvest groundcover between ameliorated and untreated (control) plots. These findings offer practical insights into the broader benefits of soil amelioration techniques beyond their primary targets, providing valuable implications for farm management decisions.

The Role of Groundcover After Harvest

Groundcover refers to the plant residue and biomass that remains on the soil surface after harvest. It plays a key role in reducing wind and water erosion, moderating soil temperature, improving moisture retention, and minimising nutrient loss. In farming systems where summer rainfall is variable and soil structure is fragile, maintaining groundcover during the fallow period is critical.

The primary aim of the 2024 trial was to assess soil amelioration methods in relation to water repellence. However, during a mid-March soil sampling visit, distinct differences in groundcover between treatments were observed (see Image 1). Four treatments were evaluated:

  • Plozza ploughing
  • Nufab deep ripping (single and double pass)
  • Plozza ‘Fanger’ mixing
  • Control (no amelioration)

These treatments aimed to reduce soil water repellency, alleviate compaction, and enhance crop performance. Observations made post-harvest suggest that amelioration also contributed to increased groundcover, particularly where treatments disrupted weed seed banks and improved crop biomass.

Image 1. Visual groundcover between Nufab (single pass) (left) and control plot (right), March 2025.
Tracking Biomass and Groundcover via NDVI and Satellite Imagery

Satellite imagery—including Normalised Difference Vegetation Index (NDVI) and high-resolution colour imagery—was used throughout the 2024 season to track changes in plant health and groundcover. NDVI is a reliable indicator of photosynthetic activity and biomass, while colour imagery provides visual evidence of plant density and canopy closure.

Satellite data from 19 June, 19 July, 17 September, 17 October, 16 November, and 16 December 2024 showed clear temporal trends. Early in the season, NDVI values were higher in control plots, likely due to weed growth (notably capeweed and ryegrass), which inflated biomass measurements but competed heavily with crops. As herbicide treatments took effect and crop development progressed, NDVI in control plots declined while values in ameliorated plots increased.

By December, the contrast between treatments was clear. Colour imagery showed reduced groundcover in control plots, whereas ameliorated areas maintained dense, healthy biomass well into the post-harvest period. This suggests that ameliorated soils better supported crop growth and retained groundcover benefits into the summer.

Table 1. Satellite imagery of NDVI and colour at trial site across the 2024 season (DataFarming platform).

DateNDVI ObservationsColour Imagery Notes
19/06/24High NDVI in control due to weed presenceEarly crop establishment phase
19/07/24Decline in NDVI in control plotsCrop canopy developing in ameliorated plots
17/09/24NDVI crossover beginsVisual greening in treated plots
17/10/24Strong NDVI in ameliorated plotsAdvanced growth and better biomass
16/11/24Continued biomass growth in treated plotsDeclining groundcover in control
16/12/24Highest biomass in ameliorated plotsStark groundcover difference visible
Weed Pressure and Biomass Development

Weed presence significantly influenced biomass patterns throughout the trial. In untreated control plots, weed burden was initially high, resulting in elevated NDVI. However, after knockdown herbicide applications, weed cover diminished and crop performance lagged behind that of ameliorated plots.

Amelioration treatments improved early-season weed control by burying weed seeds and disrupting germination. As a result, crop growth was less restricted, biomass was higher at key growth stages (e.g. GS30 and anthesis), and post-harvest groundcover was visibly stronger.

This shift in competitive dynamics—once crops became dominant—was reinforced by stronger root systems and improved water availability. The combination of fewer weeds and healthier crops contributed to sustained groundcover through to late summer.

mage 2. Visual difference in weed populations: Nufab (single pass) (left) vs control (right), August 2024.
Image 3. Drone image of trial site, October 2024, showing variation in biomass and canopy coverage.
Why This Matters for Farmers

Maintaining groundcover after harvest is vital for protecting soil health, particularly in fragile or water-repellent soils like those common in Dandaragan. Soil amelioration techniques that improve crop biomass during the season can contribute to significantly improved groundcover during the fallow period.

Improved groundcover offers several benefits:

  • Reduces erosion from wind and water
  • Enhances moisture retention for following crops
  • Supports soil microbial activity and nutrient cycling
  • Minimises the need for costly post-harvest erosion control

By improving crop establishment and reducing early-season weed pressure, amelioration treatments offer both agronomic and environmental gains. These benefits may be especially valuable in years with challenging seasonal conditions.

Future Research Opportunities

The promising results from this trial point to a need for further research into the post-harvest benefits of soil amelioration. Future studies should explore:

  • Long-term effects on groundcover and erosion control
  • Interactions with soil microbial communities
  • Integration with weed management programs
  • Variability across soil types and seasonal conditions

Understanding these dynamics will help fine-tune amelioration techniques to maximise both productivity and soil health.

Conclusion

Soil amelioration has demonstrated the potential to significantly enhance post-harvest groundcover by improving biomass production and reducing weed pressure. These outcomes provide farmers with practical tools to improve soil condition, reduce erosion risk, and better prepare paddocks for the following season. As farming systems continue to adapt to climate variability and soil constraints, integrating amelioration into broader soil and crop management strategies will be key to building resilience and long-term productivity.

Tackling Constraints and Driving Change at the 2025 WMG Crop Research Updates

By Simon Kruger & Kate Parker

The West Midlands Group’s 2025 Crop Research Updates brought together over 30 local farmers, agronomists, and industry representatives for a day of research-driven discussion and practical insight into crop performance, soil health, weed management, and emerging agronomic technologies. Held alongside the WMG Annual General Meeting and followed by a Sundowner BBQ sponsored by Rabobank, the event highlighted how targeted, regionally relevant research is supporting innovation and resilience across the West Midlands.

Soil Constraints and Fertiliser Efficiency

Dr Gaus Azam, from the Department of Primary Industries and Regional Development (DPIRD), opened the day with an overview of fertiliser use and soil characteristics in WA. He emphasised that nitrogen use efficiency in the region remains low—often around 30%—with substantial losses attributed to leaching. Dr Azam also reflected on the broader context of soil acidity management in the 1990s and the ongoing legacy of WA’s ancient, highly weathered sandy soils, which typically lack silt and have poor nutrient-holding capacity.

Kanch Wickramarachchi, also from DPIRD, presented findings from re-engineering trials designed to address the physical and chemical limitations of WA’s sandy soils. Treatments ranged from deep ripping with lime incorporation to more intensive interventions including claying, organic amendments, and nutrient layering. These treatments, trialled in locations such as Bolgart, Grass Valley and Badgingarra, showed substantial improvements in root development, water use efficiency, and yield—offering a promising pathway for improving productivity in severely constrained soils. Kanch also provided an update on the establishment of a local trial site at the Kenny family’s property near Badgingarra, which will contribute valuable regional data to support ongoing assessment of soil amelioration practices in broadacre systems.

Weed Management Innovation

Dr Mike Ashworth (AHRI) delivered a timely update on current and emerging weed management strategies. His message was clear: effective weed control starts with crop competition, not herbicides. Research trials showed that increasing seeding rates in wheat and canola suppressed weed growth without yield penalties, challenging long-held assumptions.

Dr Ashworth also discussed the risks of complacency in Harvest Weed Seed Control (HWSC). Wild radish, for example, has evolved strategies such as pod shedding to evade HWSC capture. Maintaining control requires vigilance: managing early germinations, varying crop and harvest timings, and using precision tools such as remote sensing to track patches. He noted that AHRI, with support from GRDC, is actively exploring LIDAR and other technologies to improve in-season weed detection.

Stubble Management Learnings from Local Practice

As part of the State NRM-funded Stubble Management Project, two grower-presenters—Ash Jacobs and Connor Baker—were invited to share their on-farm learnings with the local grower community.

Ash Jacobs, a fourth-generation farmer from Corrigin, reflected on the transition to a strip and disc seeding system over the past decade. The system has nearly doubled crop yields, despite similar rainfall, by improving moisture retention and erosion control through tall stubble and continuous ground cover. While challenges remain—particularly with pre-emergent herbicide safety, hairpinning, and stubble shading—Ash noted the importance of adapting the system year-on-year and using standing stubble to hold summer rainfall until seeding.

Connor Baker, a research agronomist with the Corrigin Farm Improvement Group (CFIG) and fourth-generation grower, shared his strategies for managing fragile white sands through continuous cropping, stubble retention, and targeted incorporation of organic matter. He is trialling angled seeding to preserve stubble cover and using speed tillage to blend residues into sandier patches. His long-term goal is to build soil structure, reduce nutrient losses, and improve water use efficiency—key priorities in managing marginal soils.

Markets and Crop Outlook

Henry Carracher, from CBH Group, provided an overview of current market conditions and crop performance. Unexpectedly high yields were recorded across the region, despite average rainfall, which he attributed to excellent in-season rainfall use and possible reductions in livestock pressure. Henry described the current grain market as “non-fundamental,” driven by unpredictable geopolitics and soft demand for key commodities such as malt and canola. He noted that global trade tensions continue to influence Australian grain exports, particularly in relation to China.

Fertiliser Trials and Agritech

Alana Alexander, from Summit Fertilizers, presented results from long-term potassium trials, which suggest that 30 units of K delivers the strongest gross margins across multiple seasons. She also introduced the benefits of N Shield, a nitrogen management product offering protection against volatilisation and leaching in high pH, low organic carbon soils. By reducing nitrogen losses, the product provides growers with greater flexibility in fertiliser timing—particularly important in variable seasons.

Several emerging technologies were also discussed:

  • CropX soil moisture probes, which provide real-time insights into soil moisture, temperature, and salinity to inform seeding and nitrogen decisions.
  • Biowish microbial fertiliser coatings, designed to enhance nutrient uptake and increase root biomass. Trial data showed average wheat yield gains of 6.5%, with protein increases between 0.5% and 1%, particularly when applied early in the growing season.
Thank You

The West Midlands Group extends its sincere thanks to everyone who attended the 2025 Crop Research Updates. Your ongoing support, engagement, and interest in research-driven farming are what make these events so valuable for our region. We are especially grateful to our speakers for generously sharing their time, experience and insights, and to Rabobank for sponsoring the Sundowner BBQ. Events like these reflect the strength of collaboration in our agricultural community, and we look forward to continuing to learn and grow together.

Understanding Soil Water Repellence: Causes, Risks and Management Options

By Kate Parker & Simon Kruger

Introduction

Soil water repellence (also known as non-wetting soil) is a widespread constraint in Australian farming systems, particularly in sandy soils of the southern and western grain-growing regions. It can have significant implications for crop establishment, water use efficiency, erosion risk, and overall productivity. This information piece outlines the causes, contributing factors, and management options to address soil water repellence in broadacre cropping systems.

This information piece was developed as part of the GRDC-funded Soil Water Repellence Project. For more information on the project and local trial results, visit the West Midlands Group project page.

The 2024 Soil Water Repellence Project trial site in Dandaragan
What Causes Soil Water Repellence?

Soil water repellence occurs when individual soil particles—particularly sand grains—are coated in hydrophobic (water-repelling) substances. These waxy organic coatings are primarily derived from plant residues and the by-products of biodegradation. Instead of infiltrating evenly into the soil, water runs off, pools, or follows preferential pathways (such as bio-pores), reducing the uniform wetting of the soil profile.

  • Soils with a small surface area, such as sand, are more prone to water repellence because less hydrophobic material is required to coat each particle.
  • More than 50 plant species, including some commonly grown pasture legumes such as clovers and lupins (particularly Lupinus cosentinii), have been implicated in increasing repellence.
  • Native species such as Eucalyptus astringens (brown mallet), Eucalyptus patens (blackbutt) and Banksia speciosa (showy banksia) are also associated with severe water repellence.

Cereal crops do not typically contribute to water repellent residues.

Contributing Factors in Modern Farming Systems

Several management practices and environmental trends contribute to the severity and persistence of water repellence:

  • Dry Autumns: Reduced frequency and intensity of autumn rainfall events limits the opportunity for the repellent soil layer to wet up at the break of the season.
  • Dry Seeding: An increase in dry sowing practices means repellent topsoil is more likely to flow into the furrow, surrounding the seed and fertiliser.
  • Narrow Point Seeding: Knife points can exacerbate the issue by concentrating repellent soil in the seed row.
  • Reduced Cultivation: No-till systems concentrate organic material near the surface, leading to more severe repellence.
  • Sheep Camps: Accumulation of organic material and ineffective breakdown of waxy residues in dung can increase repellence.
Biological Breakdown and Soil Microbial Activity

Under moist conditions, soil microbes—particularly certain bacteria—can break down the hydrophobic waxes. However, during prolonged dry periods, microbial activity is limited, and repellence persists.

Interestingly, when repellent soil is buried at depth (e.g. through soil inversion), it tends to wet up due to hydraulic pressure from the surrounding soil. This promotes microbial activity and leads to gradual breakdown of waxes over time. However, the process may take several years, depending on moisture availability.

Management and Amelioration Options

Several proven techniques are available to address water repellence, particularly in sandy and gravelly soils:

1. Soil Inversion

  • A one-off renovation technique where the repellent topsoil is buried to 15–35 cm using mouldboard, square or modified disc ploughs.
  • Effectively inverts the soil profile, creating a fresh, non-repellent topsoil surface.
  • Provides long-term benefit (up to seven years or more) and can reduce herbicide-resistant weed seed banks.
  • Most effective in the Northern Wheatbelt.
  • Care is needed to prevent erosion following inversion.

2. Rotary Spading

  • Involves deep mixing of repellent topsoil and subsoil using a rotary spader.
  • Lifts clay seams or moisture-retaining subsoil to the surface, creating infiltration pathways.
  • Benefits last 3–5 years and it is a suitable method for incorporating lime or other amendments.

3. Disc Ploughing

  • Less aggressive than inversion or spading.
  • Dilutes the repellent layer, particularly useful on sandy gravels with natural erosion resistance.

Each of these tillage methods can disrupt the repellent layer, improve moisture penetration, and assist with weed control. Selection should be based on soil type, erosion risk, machinery access, and desired longevity of treatment.

Re-Development of Repellence After Amelioration

The timeframe for re-development of soil water repellence after amelioration depends on the nature of the new topsoil:

  • Subsoils with higher clay content are slower to redevelop repellence.
  • Organic inputs (such as stubble from legumes or certain pastures) may accelerate the return of repellence over time.

In some inverted sandy soils, no signs of renewed repellence were observed for 5–6 years after treatment.

Conclusion

Soil water repellence remains a key constraint on crop establishment and water use efficiency across many Western Australian farming systems. It is most severe in sandy soils, particularly under systems with dry autumns, reduced cultivation, or high organic inputs from certain species.

Fortunately, several management options—including soil inversion, rotary spading, and disc ploughing—are available to address this issue. These strategies improve infiltration, support better plant growth, and provide benefits for erosion control and weed management.

Ongoing monitoring and further research will help refine best practices and ensure long-term outcomes from these interventions.

References & Further Reading:

Bringing Regions Together Through Stubble Management: Shared Learnings from Corrigin to the West Midlands

By Simon Kruger & Kate Parker

As the State NRM funded Stubble Management Project draws to a close, a recent knowledge-sharing visit by Corrigin farmers Ash Jacobs and Connor Baker to the West Midlands region provided a fitting finale to this cross-regional initiative. A collaboration between the Corrigin Farm Improvement Group (CFIG) and the West Midlands Group (WMG), the project has focused on exploring practical stubble management techniques to enhance groundcover, improve soil function, and support climate resilience across two of Western Australia’s major grain-producing regions.

The visit marked a valuable opportunity for West Midlands growers to hear firsthand how stubble management is being approached in the Central Wheatbelt, and to reflect on shared challenges, innovations, and outcomes from both regions involved in the project.

Closing the Loop on Collaborative Learning

Throughout the Stubble Management Project, both Ash and Connor have played an active role in trial design, practice change, and grower engagement in the Corrigin district. By travelling north to meet with West Midlands growers, they helped close the loop on a project that was always intended to bring communities together through applied learning.

Ash Jacobs, a fourth-generation grower from Corrigin, has spent more than a decade refining his stubble management practices to address issues such as erosion, moisture loss, and delayed sowing. His use of a strip and disc system has provided consistent soil cover, reduced harvest time, and improved summer rainfall retention. Ash spoke about the importance of adapting systems annually, noting that stubble isn’t just a residue to manage—it’s a resource that, when handled well, supports the productivity of the next crop.

Connor Baker, a research agronomist with Corrigin Farm Improvement Group (CFIG), brought a complementary perspective grounded in soil structure, nutrient dynamics, and crop rotation planning. His presentation highlighted how continuous cropping systems in the eastern wheatbelt are relying on stubble cover to hold fragile sands, build organic matter, and retain applied nutrients. His insights helped bridge the connection between stubble management and broader goals like improving water use efficiency and reducing nutrient loss.

Shared Results and Real-World Application

The Stubble Management Project has involved six demonstration sites across the Northern Agricultural Region and Central Wheatbelt, comparing three practical treatment approaches:

  • Standing stubble left untouched
  • Mechanical manipulation using tools such as stubble crunchers
  • Pre-seeding applications of nitrogen or biostimulants to support stubble breakdown

Trial sites were established under commercial conditions, with the aim of evaluating each treatment’s influence on stubble decomposition, nutrient cycling, seeding operations, and early crop establishment. Importantly, the project also looked at how these effects vary between regions with different rainfall, soil types, and farming systems.

Ash and Connor’s presentations provided West Midlands growers with a chance to reflect on the outcomes seen in Corrigin—particularly where similar tools or practices had been trialled—and to discuss how different strategies could be adapted locally.

A Project Built on Partnership

The exchange between CFIG and WMG has reinforced the value of regional partnerships in addressing shared agronomic challenges. While farming systems and soil constraints may differ between the Central Wheatbelt and the Northern Agricultural Region, the core goals remain the same: improving groundcover, retaining moisture, reducing erosion risk, and building more resilient cropping systems in a changing climate.

By bringing farmers together to compare approaches and outcomes, the Stubble Management Project has helped ensure that the findings are practical, regionally relevant, and grounded in lived experience.

West Midlands Group would like to sincerely thank Ash Jacobs and Connor Baker for making the journey north to share their experiences, and to all growers and partners who contributed to the success of the Stubble Management Project. The connections built between regions have helped translate research into action—and created a strong foundation for ongoing collaboration in soil stewardship and sustainable cropping.

For more information on the Stubble Management Project and outcomes from the trials, visit the WMG project page.

Hands-On Spray Workshop Equips Growers with Next-Level Spray Efficiency Insights

By Simon Kruger & Kate Parker

The West Midlands Group recently hosted a three-quarter-day workshop at the Dandaragan CRC and Kayanaba Farm, with support from the Grains Research Development Corporation (GRDC), bringing together 35 farmers and industry representatives keen to sharpen their spray application techniques and enhance on-farm efficiency.

Led by agronomist and application specialist Bill Campbell, the session combined theory with paddock demonstrations and showcased the importance of correct sprayer set-up, calibration and chemical handling. Participants explored essential spraying principles such as droplet coverage, spray quality, and product delivery, while also considering how to optimise sprayers for knockdowns, fungicides and pre-emergents.

The workshop went beyond routine discussion of nozzles and spray quality to address different spraying systems, including hydraulic nozzles versus pulse width modulation (PWM), enabling growers to tailor equipment to various product types and reduce waste through effective drift management. Live demonstrations emphasised best-practice mixing and batching techniques, reinforcing the value of stable ground speeds, appropriate nozzle selection and thorough coverage.

Attendees were also encouraged to consider the latest innovations in agricultural technology, including an introduction to the SwarmFarm sprayer bot, which illustrated the potential of autonomous machines to boost efficiency and reduce environmental impact. Bill Campbell’s guidance underscored practical ways to keep operational costs manageable, highlighting the benefits of effective travel routes to filling points and the advantages of safe, efficient batching or mixing systems.

Growers and their employees departed with a deeper understanding of how to apply different products—such as herbicides, fungicides and insecticides—more effectively, whether they were contact or systemic in nature. By observing the equipment in action on Kayanaba Farm, participants gained confidence in their ability to set up and calibrate sprayers for a range of spraying situations, aligning with ongoing GRDC commitments to practical, face-to-face learning.

The West Midlands Group thanks everyone who joined the GRDC Spray Workshop and SwarmFarm Demo, including those who took part in both the theory session and paddock exercises. Special appreciation goes to Bill Campbell for sharing his expertise, Tom Holcombe for organising the autonomous robot demonstration, and Charles Roberts for generously hosting activities on Kayanaba. The day’s interactive format fostered valuable discussions and hands-on experiences, supporting local growers in making informed decisions to improve spray efficacy, efficiency and safety on their farms.

Helping Farmers Make More Informed Decisions: The Risk/Reward Tool

By Simon Kruger, WMG Project Communications Officer

Farmers face no shortage of information when it comes to adopting new practices—but too often, that information is difficult to interpret or apply. Research reports can be technical, narrowly focused, or simply not designed with the realities of on-farm decision-making in mind.

The Risk/Reward Tool Project, funded by the CRC for High Performance Soils (Soil CRC), led by the West Midlands Group and delivered in collaboration with Charles Sturt University, set out to address this issue. Working alongside two other Farming Systems Groups—Corrigin Farm Improvement Group (Western Australia), and Central West Farming Systems (New South Wales)—the team co-developed the Risk/Reward Tool, a practical framework to improve how research findings are communicated to farmers.

Why It Was Needed

Many farmers weigh up far more than short-term profitability when making decisions. Risk, labour implications, environmental benefits, long-term soil health, and social licence all factor into how and whether a new practice is adopted. But most reporting formats still focus on economic results, without contextualising trade-offs or linking findings to the bigger picture.

This project recognised that reporting isn’t just about sharing information—it’s about enabling decisions. To do that, the communication format itself needs to work better for both the people writing the reports and those reading them.

What the Tool Offers

Developed through a co-design process with the three Farming Systems Groups, the Risk/Reward Tool supports layered communication through three formats:

  • A one-page infographic for quick insight
  • A four-page synthesis report with moderate detail
  • A comprehensive technical report for in-depth analysis

Each format incorporates financial, environmental, social, and governance considerations—helping farmers understand not just the benefits of an innovation, but also the potential risks or trade-offs.

An accompanying writing guide helps extension staff use the tool consistently and effectively, while still allowing for local tailoring.

An example of an Infographic produced as part of the Risk/Reward Tool Project
What We Learned

Feedback from participating groups and their farmer members showed that the tool made information easier to digest and apply. The infographic and synthesis report, in particular, were seen as useful formats for early decision-making. Extension staff noted that the tool improved internal consistency and reduced the need to recreate reporting formats from scratch. At the same time, challenges remain around embedding new tools into existing workflows—especially in organisations affected by staff turnover.

What’s Next

While the Risk/Reward Tool shows promise, further work is needed to understand where and how it fits best within the diverse reporting environments used by Farming Systems Groups. The project has opened up useful conversations about the role of extension in not only delivering information, but in shaping how farmers engage with complex decisions.

There may be opportunities to explore how the tool could support other Soil CRC projects or be adapted to different regional or enterprise contexts. Interest in digital delivery and integration with other farm planning tools has also been raised, although these directions would require further scoping and resourcing.

What the project has confirmed is that farmers value concise, comparative information that reflects their realities—not just economic outcomes, but environmental and social considerations too. Tools that enable this kind of communication have a role to play in improving both the quality of extension and the confidence with which farmers adopt new practices.

Optimising Potassium Management in the West Midlands: Results, Analysis and Insights from 2024 Trial Sites

By Kate Parker, Simon Kruger & Nathan Craig, WMG

Overview

Potassium (K) deficiency remains a significant constraint to crop productivity across the sandy soils of the West Midlands region, WA. Local growers frequently note uncertainty around optimal potassium management, including application rates, placement, timing, and the capacity of various crops to recycle potassium from deeper soil layers. Responding to these concerns, the West Midlands Group (WMG) conducted detailed trials as part of the GRDC funded K Extension Project in 2024 at two locations—Dandaragan and Badgingarra—to assess different potassium management strategies and crop responses.

Dandaragan Trial Site: Investigating Crop Responses to Deep Ripping

The K Extension Project Dandaragan trial site.
Context and Methodology

At the Dandaragan site, the main research objective was to evaluate how different crop types (short and medium-season wheat, canola, lupin, and serradella) utilise potassium from deeper soil layers. With evidence of substantial subsoil potassium, there was interest in determining if deep ripping post-seeding could enhance crop access to these deeper reserves.

Researchers established replicated trial plots, with half deep-ripped to a depth of 60cm post-seeding and half remaining unripped. The crops were monitored closely throughout the growing season for plant establishment, soil strength, biomass production, potassium uptake, and grain yield.

Key Findings

Plant establishment results demonstrated that early post-emergent deep ripping generally reduced plant numbers initially, particularly affecting wheat and serradella. Surprisingly, canola and lupin, with lower seeding rates and larger seeds, appeared relatively unaffected.

Deep ripping markedly reduced soil strength, allowing easier root penetration down to approximately 650mm, compared with just 225mm in unripped plots. Despite these soil condition improvements, the overall biomass production benefit was less clear, with no statistically significant advantage for deep-ripped plots on average. However, specific crop species showed noteworthy trends:

  • Canola and lupin biomass production improved substantially with ripping, bringing their production levels closer to wheat.
  • Serradella biomass had a significant benefit from deep ripping but only by the end of the season was this trend clear.
  • Mid-season and Short-season wheat notably benefited from deep ripping for grain yield, even though initial plant establishment was reduced; Medium season wheat had the highest grain yield at 3.3t/ha
Figure 1. Grain Yield of different crop species at the Dandaragan site in 2024, comparing ripped versus not ripped plots. Error bars denote the standard error of the treatment mean. Lower case letters denote significant differences (P<0.05) within treatment groups, ns = no-significant difference.
Potassium Uptake Results

Interestingly, wheat (particularly mid-season varieties) emerged as the most effective at recycling potassium to the soil surface, despite assumptions that deeper-rooted crops like lupin, canola, and especially serradella would excel at accessing deeper potassium reserves. Serradella, although known for deep roots, demonstrated the lowest biomass and potassium uptake in its establishment year.

A strong relationship was observed between crop biomass production and potassium uptake across the trial (R²=0.81). This clearly indicates that the amount of potassium cycling through crops is closely tied to biomass production rather than the depth or extent of root systems alone.

Figure 2. Relationship between plant biomass and Potassium (K) uptake across all treatments at site 1 (Dandaragan) in 2024.

Badgingarra Trial Site: Evaluating Potassium Application Rates, Placement and Products

The K Extension Project Badgingarra trial site.
Context and Methodology

The Badgingarra trial explored different potassium fertiliser rates (Nil, K15, K30, K45, and K75), fertiliser products (Muriate of Potash – MOP, and Sulphate of Potash – SOP), and fertiliser placement strategies (banded with seed versus below seed placement) on wheat crop establishment, growth, potassium uptake, and yield.

Key Findings

Plant establishment decreased slightly at higher potassium fertiliser rates (especially K45 and K75) when fertiliser was applied directly with seed. This was consistent with previous research indicating potential establishment risks with high potassium rates placed too close to emerging seedlings. However, despite this early setback, the crop was generally able to compensate, with minimal impact on final biomass and yield.

At Growth Stage 30 (end of tillering), biomass production was notably highest at the moderate K30 rate. Higher rates (K45 and K75) showed no additional biomass advantage. Unsurprisingly, the absence of any fertiliser (Nil Fert) resulted in significantly lower biomass, however the plant analysis showed that the potassium % in the crop was sufficient and there was no adverse effects at plant establishment. This suggests that potassium alone wasn’t limiting early growth—other nutrients were implicated and earlier plant analysis may be necessitated to catch this deficit before it affects crop growth.

Peak biomass and potassium uptake confirmed that the K30 rate appeared optimal for total seasonal potassium uptake, providing no advantage at higher rates. Placement method and fertiliser product type (MOP vs SOP) did not significantly impact biomass or potassium uptake.

A clear correlation between biomass production and potassium uptake was evident (R²=0.58), reinforcing findings from the Dandaragan site. This suggests the key to effective potassium utilisation lies in ensuring adequate nutrition across all nutrients to maximise biomass growth, rather than relying solely on potassium rate or product.

Figure 3. Relationship between plant biomass and Potassium (K) uptake across all treatments at site 2 (Badgingarra) in 2024.

The grain yield of all treatments where potassium fertiliser was applied (K15, K30, K45, K75) were all statistically similar in grain yield compared to the Nil K control treatment (Figure 4). While not significant, there was a trend that grain yield was maximised where 30 kg K/ha (K30) was applied, and all treatments had a higher grain yield compared to the Nil Fert treatment.

Figure 4. Yield (t/ha) in wheat for fertiliser rate (placement and type of fertiliser treatments were not significant and ? not shown) treatments at the Badgingarra site in 2024 (Harvested 6/11/2024). Dotted lines indicate average yield of wheat on the site in 2020, 2021 and 2024 for comparative purposes. Error bars denote the standard error of the treatment mean. Lower case letters denote significant differences (P<0.05) within treatment groups.
Practical Implications for West Midlands Growers
Soil Testing and Monitoring
  • Regular comprehensive soil tests, including subsoil layers, are recommended to understand potassium reserves and formulate fertiliser strategies. The results from this trial indicate that monitoring potassium levels down to 90cm to detect reserves available deeper in the profile may be beneficial.
Deep Ripping Considerations
  • Growers should consider deep ripping where compaction limits crop productivity, particularly for wheat varieties and potentially lupin and canola. However, serradella may not immediately benefit in respect to biomass until late in the season.
  • Early post seeding ripping shown in this trial site indicate some benefits thus presenting growers with an alternative to pre-seeding ripping if conditions and timing are not optimal. Care should be taken when considering this method in respect to crop type, the window between seeding and deep ripping, and the type of deep ripping machine used.
  • It’s important to carefully evaluate the economic trade-offs of deep ripping. In soils where potassium is abundant at depth and surface compaction limits root growth, deep ripping can offer longer-term benefits, although immediate yield responses may not always be clear or consistent.
Potassium Application Strategies
  • Moderate potassium application rates around 30 kg K/ha appear optimal, balancing improved biomass production and cost-effectiveness. Higher rates showed diminishing returns, particularly on sandy soils similar to those at Badgingarra. This does not necessarily mean the fertiliser would be wasted; as the crop only takes up what it needs in season, the excess fertiliser would reside in the soil and could either be lost through leaching and volatilisation or has the potential to be used in the future as shown in principles such as N-banking. The trial site this past year did not collect data on long-term soil reserves of fertiliser however future trials are being planned to assess the efficacy of N-banking strategies for soil types and rainfall patterns common in the West Midlands region.
  • Placement of potassium fertiliser away from the seed row is recommended where higher rates are used, mitigating the risk of poor early establishment. However, modest reductions in plant numbers observed at higher seed-placed potassium rates had minimal impact on final biomass and yield, indicating some flexibility.
Potassium Cycling connection to Biomass
  • In the Dandaragan Trial, wheat emerged as the most effective in recycling potassium compared to other crops largely due to its high biomass production. Growers might leverage this characteristic strategically by focusing on optimising biomass production.
  • This trend was also evident in the Badgingarra trial with Potassium uptake coinciding with biomass production and not so much fertiliser strategies.
Conclusion

The 2024 trials provide valuable insights into potassium management within the West Midlands farming region. While these results are promising, they underscore the importance of carefully balancing potassium rate, placement, crop choice, and soil management practices for optimal crop performance. Growers should remain cautious in extrapolating the trial findings broadly, recognising the influence of seasonal variability and specific site conditions.

The West Midlands Group will continue investigating these key questions, building a stronger evidence base for potassium management strategies that enhance productivity and sustainability. Farmers are encouraged to engage with ongoing research, share experiences, and adopt tailored potassium management approaches to suit their specific farm context.

Further information and ongoing updates from the K Extension Project can be found on the project page.

Evaluating the Economics of Soil Amelioration Strategies for Non-Wetting Soils

By Kate Parker & Nathan Craig, WMG

Key Takeaways
  • Plozza Plow emerged as the most cost-effective treatment, with the highest yield and return on investment (ROI).
  • Soil amelioration treatments outperformed untreated plots, with significant yield increases in 2024.
  • Early results suggest that Plozza Plow offers the best financial returns, with the fastest break-even period.
  • These results are based on trial data from 2024, and further research is needed to assess long-term benefits.
Introduction

Non-wetting soils are a significant challenge for farmers in the Geraldton and Kwinana West Port Zones. Water repellence on sandy and gravel soils leads to poor crop germination, lower yields, and inefficient fertiliser use. The Soil Water Repellence project is addressing this issue through a Participatory Action Research (PAR) approach, testing various soil amelioration techniques to improve water infiltration and crop establishment. The goal is not just to find effective practices but to evaluate their economic feasibility.

Economic Considerations

While improving soil health is crucial, understanding the economic viability of these practices is equally important. Valuable data on the cost-effectiveness of different treatments, can assist farmers in making informed decisions about which practices to adopt based on their potential ROI.

An economic analysis will assess:

  • The cost of machinery and amendments
  • Expected improvements in crop yield
  • The economic return over multiple growing seasons

This analysis will initially focus on the 2024 season, providing preliminary data to guide farmers. A full economic report will follow at the conclusion of the project, taking into account long-term results.

Challenges and Limitations
  • Climate & Soil Type Variability: The results of this trial are based on the specific soil types and climate conditions in the Geraldton and Kwinana West Port Zones across one season. Variations in these factors may influence the outcomes.
  • Machinery Costs: The estimated machinery costs are provided by the participating growers, which may vary depending on equipment availability and usage rates.
2024 Economic Analysis Results

The table below summarises key results from the trial conducted at the Dandaragan site in 2024. Peak biomass was measured at the anthesis stage of oats, while grain yield was calculated using the grower paddock yield map at harvest. Gross Margin is calculated using a figure of $390/tonne for milling oats. (This table has been reduced from its original full analysis for ease of reading).

Table 1. Peak biomass and grain yield for each soil amelioration treatment at the Dandaragan site in 2024. Peak biomass was measured at the anthesis stage of the oats while grain yield was measured using the grower paddock yield map at harvest. Gross Margin has been calculated using the grower-based figure of $390/tonne for milling oats.

MeasurementPlozzaFangerControl 1NufabControl 2Nufab Dbl
Peak Biomass (t/ha)6.88.95.58.54.77.8
Biomass benefit (% of average control treatments)+34%+75%0%+68%0%+53%
Grain yield (t/ha)3.23.01.82.81.62.8
Yield benefit (% of average control treatments)+89%+76%0%+65%0%+64%
Harvest Index47.2%33.6%32.5%33.1%34.7%35.8%
Yield Income ($/ha)$1252$1166$698$1096$636$1088
Gross Margin ($/ha)$961$876$408$805$346$798
Capital Investment (estimated by those involved)$63$147–$130–$243
Net difference after investment (Gross Margin)$491$322–$268–$147
Return on Investment (% Return)876%319%–307%–160%
Breakeven period (Years to return on investment)*0.10.3–0.3–0.6
*Note: As grain farming only has returns once a season (in this context), breakeven time below 1 year simply means that it is expected to get a return on investment within the first year of implementation of the treatment.
Figure 1. Grain yield for soil amelioration treatments in 2024.
  • Plozza Plow Treatment: This treatment achieved the highest average yield (3.21 t/ha), an 89% yield increase over untreated plots, and delivered the best ROI with a break-even period of just 0.1 years—the shortest among all treatments. Despite lower operational costs, this treatment provided remarkable returns for farmers.
  • Fanger Plow Treatment: While it also showed good yield improvement, it had higher costs and a longer break-even period compared to the Plozza Plow.
  • Nufab Rip/Delve Treatments: These treatments also provided yield improvements, but they required higher investment and had longer payback periods.

The economic analysis confirmed that the Plozza Plow offered the highest ROI (876%), delivering substantial returns with minimal additional investment. The treatment required less fuel and machinery time, making it highly efficient for farmers.

The Plozza Plow treatment this year has demonstrated a low operational cost, quick break-even period and high yield benefit. The gross margin for this treatment also showed the most significant increase, reinforcing its value as a profitable soil amelioration technique.

While the 2024 results are promising, further research will be crucial in understanding the long-term benefits and sustainability of these treatments. The soil types, rainfall patterns, and other variables across the region can affect the long-term effectiveness of these approaches. Ongoing monitoring and trials will provide more clarity on how these treatments hold up over multiple seasons and under different conditions.

Harvest Index

Harvest index (HI) is the ratio of harvested grain to the total dry matter of a plant’s shoots. It’s a measure of how efficiently a plant reproduces. In Australia, a considered “ideal” harvest index for most cereal crops, like wheat, is typically between 0.30 and 0.45; meaning that 30-45% of the total plant biomass is made up of harvestable grain (Hunt et al., 2012).

The Plozza plow treatment had a relatively high harvest index (Table 1) indicating better yield efficiency and larger proportion of biomass allocated to harvestable product. This also indicates the treatment has allowed more balanced conditions for the crop as the crop has put more resources into producing grain rather than overall growth. Although the other amelioration treatments showed higher biomass, their lower harvest indexes could be due to the lack of rainfall at a critical point in the season (24 days in September with no rainfall) (Table 2).

The deep ripping/delving mixing mechanisms of the Fanger and Nufab treatments do allow for better root penetration and subsequent nutrient and water use however, the increased growth and biomass from this may not be able to be sustained in stressful conditions (i.e. low rainfall at critical timing).

Studies have shown links between harvest index and % of water use after anthesis (Unkovich et al., 2006; Sadras & Connor, 1991). The disced inversion mechanism of the Plozza plow may not reach as deep or reduce as much soil strength but provides a more consistent and balanced nutrient and moisture distribution closer to the surface.

Overall, the 2024 seasons data from the Dandaragan trial site shows that the Plozza plow treatment has allocated more resources to reproductive structures rather than vegetative growth than other treatments allowing for a higher harvest index.

Table 2. Monthly rainfall in 2024 and the long-term average (LTA 2005-2024) at the closest weather station to the trial site. (Nambung station (009276) – BOM)

 Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual
 2024 0 2 3 8.2 45.2 124.5 140.3 99.7 8.8 45.0 6.0 0.8484
 LTA 13.2 17 17.8 17 61.6 90.5 102.2 85.1 44.6 24.9 13.4 11.8 514
Conclusion

The trial’s results show that ameliorating non-wetting soils doesn’t just improve crop yields—it can also boost farm profitability. The soil amelioration treatments in this study demonstrate that adopting any of the methods is more profitable than continuing without them. Among the treatments tested, Plozza Plow emerged as the most cost-effective option, offering significant financial returns for farmers looking to improve yields in non-wetting areas. However, the 2024 season, with its late season break and low September rainfall, may not fully reflect the potential long-term benefits, especially if rainfall had been higher. This underscores the need for caution in interpreting the results, as rainfall variability can significantly impact crop yields. 

The study also highlighted differences in the cost and effectiveness of soil amelioration methods. The Nufab ripper, which works to a depth of 60cm, had higher costs due to equipment hire and fuel but may offer long-term benefits due to deeper soil loosening. Practicalities, such as equipment accessibility and costs, need to be considered when choosing a method. Additionally, the study’s limitations, including reliance on data from a single season and assumptions about stable input costs, suggest that long-term studies are necessary for a more accurate economic assessment.

Future research could focus on multi-season studies to assess the durability of the findings, explore other agronomic factors, and examine how soil amelioration interacts with other farming practices. A broader economic analysis, considering equipment depreciation, labour, and regional market dynamics, would provide a more comprehensive understanding of the financial impact.

As these treatments continue to be refined and tested, farmers in the Geraldton and Kwinana West Port Zones can look forward to practical, science-backed solutions for managing non-wetting soils, improving their bottom line and increasing knowledge and confidence in managing non-wetting soils.

Next Steps
  • Ongoing Monitoring: Data will continue to be collected on this trial site through to the end of the 2026 season, providing a clearer picture of the long-term impacts of the amelioration practices. More trial sites will be established across the region on varying soil types to further assess soil amelioration options.
  • Follow-Up: Farmers interested in participating or learning more should contact projects@wmgroup.org.au for further information.
References

Hunt, J., Brill, R., & DPI, N. (2012). Strategies for improving water-use efficiency in western regions through increasing harvest index.?Department of Primary Industries (DPI) NSW, Australia, p10.

Unkovich, M. & Baldock, Jeffrey & Forbes, Matthew. (2006). A review of biological yield and harvest index in Australian field crops. 

Sadras, V.O. and Connor, D.J., 1991. Physiological basis of the response of harvest index to the fraction of water transpired after anthesis. A simple model to estimate harvest index for determinate species. Field Crops. Res., 26: 227-239. 

FEED365 Summer Sheep Grazing: Implications for Paddock Management and Grazing Strategies

By Kate Parker, WMG Project Officer

Introduction

A recent grazing period at the FEED365 site in Warradarge was conducted over a 7-weeks from December to January and has provided valuable insights into the weight gain patterns of sheep and the optimal grazing duration for paddocks. The results confirm previous observations from the main FEED365 sites in Katanning and other studies (Clayton EH et al., 2024), where sheep exhibit high growth rates early in the grazing period (initial 3 weeks) that taper off as the trial progresses (last 3 weeks). This decline can be attributed to the gradual reduction in pasture quality and availability over time, leading to sheep walking greater distances to find grazable parts of the paddock. The findings have important implications for farmers seeking to optimise their grazing management to improve livestock productivity while ensuring sustainability in pasture use.

Key Findings

Weight Gain Patterns: The average daily gain (ADG) data reveals distinct patterns across different quartiles of sheep during the grazing trial:

  • Quartile 1 (Q1) saw an initial weight gain of 3.38 kg in the first 21 days, but the rate slowed, dropping to -0.57 kg by day 48.
  • Quartile 2 (Q2) exhibited consistent growth, starting with 4.00 kg gain in the first 21 days and maintaining a positive ADG throughout the trial period.
  • Quartile 3 (Q3) showed a similar trend to Q2 with a notable 4.42 kg gain in the first 21 days, followed by slower gains.
  • Quartile 4 (Q4), the heaviest sheep at the start, experienced the highest gains overall, with a 4.81 kg weight gain in the first 21 days, followed by reduced, yet steady, gains throughout the 7 weeks.

On average, all sheep in the trial saw a weight gain of 5.25 kg, with an average ADG of 0.11 kg/day. Notably, the growth rates were highest in the initial 3 weeks (Change 1) and slowed during the last 4 weeks (Change 2).

QuartileTransfer InMidwayTransfer OutChange 1ADG 1Change 2ADG 2 Change allADG all
Q127.1430.5229.953.380.16-0.57-0.022.810.06
Q229.3133.3233.824.000.190.500.024.500.09
Q330.8035.2136.664.420.211.450.055.860.12
Q433.4938.3041.314.810.233.020.117.830.16
All30.1934.3435.444.150.201.100.045.250.11
Change 1 = 21 days, Change 2 = 27 days, all = 48 days | 7 weeks, 3 weeks Change 1 and 4 weeks Change 2
Figure 1. Groundcover levels at the Warradarge FEED365 grazing trial paddock.

Grazing Duration and Groundcover: The trial demonstrated that the paddock could be grazed for a total of 7 weeks without compromising groundcover below 50%. The last measurement of groundcover, taken when the sheep were removed, indicated that grazing beyond this period could potentially harm pasture health. This underscores the importance of rotational grazing and managing paddock rest periods to ensure pasture sustainability.

Figure 2. Distribution of sheep weights at Warradarge FEED365 trial during 7-week grazing period.

Sheep Weight Distribution: The weight distribution of sheep shifted significantly over the 7-week period. Initially, the majority of sheep were within the 25-35 kg weight range. By the third week, however, the distribution peaked in the 30-40 kg range, and by the seventh week, more sheep had moved into the 40-45 kg range. This trend highlights how quickly sheep can gain weight in optimal grazing conditions, with most of the flock transitioning into heavier weight classes within the first month. The graph also shows a flattening of the distribution meaning the longer the sheep were in the paddock, the more they spread out in the weight ranges.

Weight rangeCount 1Count 2Count 3
45-50013
40-4511056
35-4012129129
30-35168186124
25-301662235
20-25323
Implications for Farmers

Early Growth Optimisation: The trial results confirm that sheep experience the most significant growth during the first three weeks of grazing, which is consistent with findings from the Feed365 Katanning trials. Farmers should consider maximising pasture quality and availability during this period to support the rapid growth phase. This could involve pre-grazing management, such as ensuring the paddock is adequately rested and that pasture conditions are favourable.

Paddock Management: Farmers should be mindful of the grazing duration to avoid compromising pasture health. While the trial demonstrated that 7 weeks of grazing did not reduce groundcover below 50%, it is critical to monitor pasture conditions closely. Rotational grazing and early exit strategies are key to maintaining pasture integrity. Overgrazing or extended grazing beyond the optimal period could lead to reduced groundcover and soil degradation.

Weight Gain and Market Readiness: Farmers targeting market-ready sheep should aim to capitalise on the high growth rates in the first 3 weeks of grazing. By adjusting grazing strategies, they can ensure that sheep enter higher weight categories within a short time frame, enhancing overall productivity and profitability.

Limitations of the Study
  • Seasonal Variation: The study was conducted during the summer months (December-January), which may not fully represent grazing conditions across different seasons. Future research should explore grazing patterns in cooler months and how pasture regrowth and sheep growth rates are influenced by seasonal changes.
  • Pasture Species: The trial was conducted on a barley paddock, which could have a significant impact on sheep performance. Further studies could investigate the effects of different forage species on weight gain and grazing efficiency.
  • Sheep Breed and Age: The trial did not account for potential differences in sheep breed or age, which may influence weight gain rates. Future trials could include a broader variety of sheep breeds and age groups to better understand how these factors impact grazing behavior and performance.
Future Research Directions

To build on the findings of this trial, several areas of research warrant further investigation:

  1. Pasture Composition and Management: Research into the impact of different pasture species and management practices (e.g., nitrogen fertilisation, irrigation) on weight gain and sustainability could provide valuable insights for farmers.
  2. Grazing Strategies and Rest Periods: Further studies on the optimal rest period for paddocks between grazing cycles could help farmers fine-tune their grazing management practices to maintain both livestock productivity and pasture health.
  3. Longer-Term Trials: Extending the trial period beyond 7 weeks could provide a better understanding of long-term grazing impacts on pasture condition and sheep performance, especially in diverse environmental conditions.
Conclusion

This trial provides practical insights into the grazing behavior and weight gain patterns of sheep over a 7-week period. While the sheep experienced the most significant growth in the first three weeks, careful management of grazing duration and pasture health is crucial to achieving optimal livestock productivity. The study reinforces the importance of rotational grazing and monitoring groundcover to maintain both sheep growth and pasture sustainability. By incorporating these insights into their grazing strategies, farmers can enhance their sheep production while ensuring long-term pasture health.

References

Clayton EH et al. (2024) Average daily gain in lambs grazing mixed annual forage species compared with single species and relationship to feed on offer. Animal Production Science 64, AN24102. doi:10.1071/AN24102

Understanding the Microbiome Responsible for Crop Residue Breakdown

By Kate Parker, WMG Project Officer

After harvest, many farmers face the task of managing leftover crop residues, including stubble, leaves, and roots. Although these residues can be difficult to handle, they play a vital role in improving and maintaining soil health. One of the main drivers of residue decomposition is the soil microbiome, a diverse community of bacteria, fungi, actinomycetes, and other microbes that break down organic matter and recycle nutrients back into the soil. By understanding how these organisms function, farmers can make better decisions about residue management, leading to healthier soils, higher crop yields, and more sustainable farming operations.

Wheat stubbles that have been machinery manipulated (left) to promote residue breakdown, and those left standing (right).
What is the Soil Microbiome?

The soil microbiome is essentially the living, active part of the soil, made up of numerous microorganisms that interact with each other as well as with plant roots. They perform critical ecological functions, such as nutrient cycling, decomposition of organic matter, and the formation of stable soil aggregates. Research by CSIRO highlights that these communities adapt to different soil conditions and climates, a factor that is highly relevant in WA due to the states soil types and rainfall varying dramatically from one region to the next.

When it comes to breaking down crop residues, specific microbes release enzymes (proteins that speed up reactions; Figure 1) that target and degrade the complex plant compounds found in stubble and other plant materials. These compounds—cellulose, hemicellulose, and lignin—are responsible for the structural strength of plants. By decomposing these materials, the soil microbiome gradually releases nutrients back into the soil. This is especially crucial in WA, where soils often have low organic matter. Increasing the organic component of the soil through residue breakdown contributes to both short-term and long-term soil fertility.

Figure 1. Enzyme activity process
How the Microbiome Breaks Down Crop Residues

Residue decomposition typically starts as soon as the plant material comes into contact with soil. Early in the process, simple compounds like sugars and proteins break down rapidly under the influence of various bacteria and fungi. As residues continue to decay, more specialised organisms take over, focusing on tougher materials such as cellulose. Certain bacteria, like Bacillus and Pseudomonas, flourish in these conditions by producing enzymes that can effectively degrade cellulose fibres.

In the later stages, fungi that specialise in lignin decomposition, including species of Trichoderma and Phanerochaete, become prominent. Lignin is one of the most rigid components of plant cell walls, and its breakdown is essential if stubble and other sturdy residues are to be fully returned to the soil’s organic matter pool. In WA’s hotter, drier areas, a lack of adequate moisture can slow this process, underscoring the need for careful moisture management. Finally, the end-products of decomposition transform into humus, a long-lasting and nutrient-rich form of organic matter that bolsters soil fertility and helps to stabilise soil structure. As this conversion unfolds, nitrogen, phosphorus, potassium, and other nutrients are gradually released, which may reduce the necessity for increased synthetic fertiliser inputs.

How the Microbiome Improves Soil Health

Microbial activity related to residue breakdown has a direct influence on several dimensions of soil health. First, as microbes decompose crop residue, organic matter levels in the soil rise, improving moisture retention and offering a stable supply of nutrients. This benefit is particularly important in WA’s sandy soils and regions with limited rainfall, where retaining moisture can determine whether a crop thrives or struggles.

Second, the by-products of microbial digestion help bind soil particles into aggregates. Aggregation (Figure 2) enhances soil porosity (spaces that can hold water or air) and aeration (movement of air in the soil) while minimising erosion—a notable concern in certain parts of WA. A well-aggregated soil is also more resilient to weather extremes, allowing it to absorb heavy downpours without collapsing. Lastly, maintaining a rich and diverse microbial community fosters soil ecosystems capable of withstanding stressors such as drought, changes in pH, or nutrient imbalances. By encouraging a broad spectrum of bacteria and fungi, farmers can establish a more robust soil environment that remains productive over a long period.

Factors Affecting Microbial Activity and Residue Breakdown

Numerous variables influence the speed and efficiency of residue breakdown in WA. Soil temperature is a critical factor; microbial activity and efficiency typically increases as temperatures rise. However, if soaring heat is coupled with limited rainfall, the resulting dry soil can slow decomposition significantly. Sufficient moisture is therefore essential to keep microbial populations active, although excessive wetness (such as waterlogging) can suppress certain microbes that depend on oxygen.

Soil pH also plays a role. Most decomposer microorganisms prefer a slightly acidic to neutral range (roughly the same conditions as the average crop), meaning that soils well outside this spectrum may require amendments such as lime to promote beneficial microbial growth. The nature of the residue itself is another determinant of decomposition rates. Materials with a high carbon-to-nitrogen (C:N) ratio (Carbon levels higher than Nitrogen), such as cereal straw, break down slowly unless adequate nitrogen sources are provided. Incorporating legumes or nitrogen-rich amendments can help balance the C:N ratio, accelerating microbial decay processes.

Lastly, soil management practices heavily influence microbial density and diversity. Excessive tillage or a restrictive crop rotation can impair microbial habitats, leading to less efficient residue breakdown. On the other hand, introducing organic matter through compost or manure, rotating different crop species, and minimising soil disturbance all support a richer microbial community capable of handling greater volumes of residue more quickly.

Managing the Microbiome for Optimal Residue Breakdown

Farmers can adopt a range of strategies to foster an environment conducive to residue decomposition. One of the most effective methods is reducing tillage, or using no-till systems, which help maintain soil structure and stability. No-till practices have already been successfully applied in much of WA, contributing to water conservation, stubble retention, and protection against erosion.

Another tactic involves regularly adding organic amendments—such as compost, manure, and green waste—that serve as additional food sources for microbes. These substances can enhance soil organic matter levels and provide the carbon and nutrients required to balance out high C:N residues. Cover cropping is similarly beneficial, especially when legume species are chosen to supply nitrogen and counteract carbon-rich debris. By planting cover crops in fallow periods, farmers can keep living roots in the soil, providing a continuous food supply for microbes and stabilising the soil against erosion.

A serradella plot at the WMG long-term Wathingarra trial site that has seen the addition of soil amendments such as compost, biochar and frass.

It is also useful to monitor soil conditions, including pH, moisture, and nutrient availability. Adjusting practices—such as the timing of residue management—can significantly impact the ability of microbes to thrive. Employing diverse crop rotations further supports microbial variety, offering an array of residue types that feed different microorganisms. By continually refining these practices based on local conditions and soil test results, farmers can ensure that their soils remain productive and biologically active year after year.

Conclusion

The soil microbiome that breaks down crop residues is fundamental to soil health and long-term productivity. When farmers nurture these beneficial microorganisms through practices like minimal tillage, the incorporation of organic amendments, cover cropping, and regular soil monitoring, they can encourage faster, more effective residue decomposition. This, in turn, improves soil structure, bolsters nutrient cycling, and reduces reliance on chemical fertilisers. In a state known for its diverse soils and climate conditions, harnessing the power of the soil microbiome can significantly enhance both farm profitability and environmental sustainability, laying the groundwork for a resilient agricultural sector.

References and Further Reading