NEWS: Green Manure Crops in Irrigated Cotton Systems Project

Thu, 17 Sep 2026 06:16:57 GMT

What the Data Tells Us

With synthetic fertiliser costs remaining high and increasing industry pressure to improve nitrogen-use efficiency and sustainability, MCA Ag Research – as part of the Cotton Research and Development Corporation (CRDC) Innovation Call - launched a feasibility study into the viability of pulse green manure crops within irrigated cotton systems.

This project evaluates whether the natural nitrogen-fixing benefits of pulse crops can outweigh the added costs of seed, management, and irrigation, helping growers make informed decisions for their rotations.

The first part of this study comprises a desktop assessment and a survey of cotton growers and consultants to understand their experiences, perceptions and willingness to adopt green manuring. The findings of this survey will help design a potential on-farm validation project.

Project Overview: Balancing Free Nitrogen with Crop Costs

A "green manure" is a sacrificial, fast-growing crop incorporated into the soil while still green to return organic matter and nutrients to the system. While historical industry studies have shown legumes fixing between 100 and 260 kg N/ha (representing significant fertiliser-replacement potential), growing a cover crop requires land, water, and management inputs.

Our study combines direct feedback from local growers and consultants with an agronomic desktop review to establish where green manure crops genuinely add value on farm.

Inspecting Faba Bean growth and biomass production in a large-scale, replicated field trial near Goondiwindi, QLD.

Industry Survey Insights: What Growers & Consultants Said

Our recent survey captured perspectives from 36 key industry respondents (58% irrigated cotton growers, 33% agronomic consultants):

Current Adoption: 75% of respondents have used cover or green manure crops, with 22% using them regularly and 53% using them occasionally. Over 90% expressed interest in adopting them or are actively using them.

Perceived Benefits: Improved soil structure and condition was cited as the top benefit ( 86% ), followed by improved water infiltration ( 64% ) and reduced synthetic nitrogen requirements ( 44% ).

Primary Adoption Barriers: The biggest hurdles preventing regular use are lack of irrigation water ( 70% ), seedbed preparation timeliness ( 56% ), and fitting crops into tight rotational windows ( 42% ).

Disease Risks Are Critical: Soil-borne disease is a major consideration. Verticillium wilt was flagged as a relevant concern by 75% of respondents and Fusarium by 61% . Notably, 83% stated that even a slight increase in disease risk would be a major concern or deal-breaker.

Species Preferences: Faba beans were the standout choice for winter green manure crops ( 67% ), while Millet/Sorghum ( 56% ), Cowpea ( 33% ), and Sunn hemp ( 25% ) led summer preferences.

Desktop Study Findings: Key Agronomic Insights

Complementing grower feedback, our technical analysis highlighted several key agronomic factors:

Starting Soil Nitrogen is Decisive: Legumes preferentially scavenge existing soil nitrogen rather than fixing atmospheric nitrogen via rhizobia symbiosis. In fields with starting soil N >50kg N/ha, N-fixation drops significantly . A survey of MCA client paddocks post-cotton harvest revealed that 26% of fields had <50kg N/ha (ideal for legume N-fixation), while 30% had high residual N where a grass cover crop would be better suited to scavenge deep nitrates.

Rotational Fit & Irrigation: Faba beans perform well in winter windows (March to August), whereas Sunn hemp offers rapid biomass production and N-fixation (up to 60-146kg N/ha in 60-90 days) during warm summer windows. Overhead irrigation systems provide greater flexibility for light establishment water compared to flood irrigation systems.

Disease Dynamics: While legumes can host certain diseases, recent commercial observations and preliminary DNA testing indicate that green manure crops like faba beans and multi-species mixes may actually help suppress Verticillium wilt and Black Root Rot DNA levels. Further field validation remains a high priority.

Active root nodulation on faba beans - the pink internal color confirms atmospheric nitrogen is actively being fixed by rhizobia.

What's Next

Survey results highlighted that comprehensive economic gross margin analyses (72%) and local trial data (61%) are essential to building grower confidence.

In addition to our CRDC feasibility study, MCA has coordinated a separate, commercial-scale replicated field trial with local MCA client Clark Farming Group (Goondiwindi, QLD) .

This project compares a faba bean green manure crop against a bare winter fallow. In collaboration with the QLD DPI Low Emissions Intensity Farming Systems (LEIFS) project and Crown Analytical Services, the trial is tracking:

Nitrogen accumulation and soil carbon levels
Soil disease DNA presence
Operational costs relative to bare fallow strips (for economic analysis)
Subsequent cotton yields

Aerial view of the commercial-scale replicated trial at Clark Farming Group (Goondiwindi, QLD), comparing faba bean manure strips against bare fallow.

A massive thank you to everyone who completed the survey and supported this initial research phase! As we finalise our feasibility reporting for CRDC, we are actively planning the next steps to bring more local data to the industry as we await outcomes for the next stage of project funding. Stay tuned for updates on trial results and future project milestones!

This project is proudly supported and funded via the Cotton Research and Development Corporation (CRDC) Innovation Call.

NEWS: Spray Drift Awareness

Sat, 30 May 2026 04:54:29 GMT

If you were lucky enough to get planting rain, let's not dampen the mood by touching up the neighbours' crops...

As we race to finish off winter planting and are trying to get pre-plant sprays done (most with Glyphosate as an inclusion), it is worth taking a breath to consider the risk of spray drift; there is still plenty of time to get our crops planted!

It is imperative to keep in mind that current conditions are creating a perfect storm for spray drift - specifically through temperature inversions. When spraying near sensitive crops, understanding the "invisible" physics of the air is the difference between a clean field and a major liability.

What is a Surface Inversion?

Under normal daytime conditions, air near the ground is warmer and rises, dispersing spray droplets upwards where they dilute. During an inversion, this process flips:

The Setup: On clear, calm nights, the ground loses heat rapidly.
The Trap: A layer of cool, dense air becomes trapped under a layer of warmer air.
The Risk: Instead of dispersing, fine spray droplets stay concentrated in a dense "cloud" near the ground. This cloud can slide sideways across the landscape for kilometres, landing on non-target cereal crops with devastating precision.

Why are we at Higher Risk Now?

May and June are particularly hazardous in our region due to several local factors:

Clear Skies & Low Wind: Our classic crisp winter nights and still mornings are the primary triggers for inversion layers.

The "Valley Effect": Many parts of the Downs and surrounding districts have subtle undulating topography. Cold air is heavier than warm air; it will literally "drain" like water into lower-lying areas, carrying glyphosate plumes directly into creek flats or sheltered paddocks where cereals are emerging.

Dry Air Persistence: Inversions here often form before sunset and can persist well into mid-morning, long after the sun has come up.

Cumulative Effect: With so much fallow spraying occurring at the same time, the amount of aerosolised herbicide adds up to create a much more risky situation. Don’t think your nozzle selection alone will keep you safe. Even if using a TTI nozzle, there is a % of driftable fines that may move off target, especially in an inversion scenario.

Glyphosate + Cereals = A Costly Mistake

While glyphosate is our go-to tool, it is non-selective . Even a low-dose drift event during the early growth stages of cereals can lead to:

Stunted root development .
Chlorosis (yellowing) of new growth.
Significant yield loss, or
Total crop failure in the affected drift zone.

Safe Spraying Checklist

To protect your and your neighbours’ crops, follow these golden rules:

Check the "Delta T": Aim for a Delta T between 2 and 8. Avoid spraying when the air is too still.
Watch the Smoke: If you see smoke/fog or dust hanging horizontally in the air rather than rising, stop immediately . This is a visual confirmation of an inversion.
Nocturnal Caution: Avoid spraying from sunset until at least one or two hours after sunrise, when the ground has had a chance to warm up and break the inversion layer.
Check your WAND Network: Before going spraying, be sure to check in with your local WAND Tower.

The WAND is a real-time hazardous weather warning system developed in Australia
It utilises a network of over 100 profiling inversion towers. These towers use remote sensing to detect hazardous temperature inversions
It updates every 10 minutes and offers a 24-hour forecast, allowing you to look 2 hours forward and 2 days back, without a subscription

The Bottom Line...

If the air is dead, keep the rig in the shed!

It's not worth the risk.

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