Read time: 4 minutes

How effective is a legume pasture phase for ryegrass control?

with Dr Yaseen Khalil, Australian Herbicide Resistance Initiative

Adding a pasture phase to a cropping rotation can take weeds by surprise and deplete a weed seed bank that has built up under a short crop sequence.

Dr Yaseen Khalil, research associate (adjunct) with the Australian Herbicide Resistance Initiative and Kaylx, says a single species pasture legume such as serradella provides multiple benefits to the system and can make a large dent in the annual ryegrass seed bank.

The AHRI agronomy team, (from left) Dr Yaseen Khalil, Roberto Lujan Rocha, Dr Mike Ashworth and Shane Baxter, compared seven crop rotations at two sites in Western Australia, including serradella pasture in one, two and three seasons.

“Pastures can be an effective tool to disrupt the evolution of herbicide resistance without compromising grain production,” he says. “Phase farming is where a multi-year pasture phase disrupts a multi-year cropping phase. The pasture phase can build soil nitrogen stores, rapidly exhaust the weed seed bank and suppress soil-borne crop pathogens.”

With investment from the Grains Research and Development Corporation (GRDC), Yaseen and other researchers investigated the effect of seven cropping rotations in high-weed-pressure fields at Bolgart and Brookton in Western Australia during the 2019, 2020 and 2021 winter growing seasons.     

“At both sites, the more diverse rotations were as effective at reducing annual ryegrass seed production as three years of winter chemical fallow,” says Yaseen. “Diverse crop rotation is a key component in the WeedSmart Big 6 integrated weed management program. In a diverse rotation, there are many opportunities to include crops or pastures with additional rotational benefits.”

What effect did rotation have on the annual ryegrass seed bank?

In brief: Seven rotations were tested at the two sites, including serradella pasture in one, two and three seasons.

The details: The ‘worst’ rotation from a weed seed bank perspective was three successive wheat crops. In this rotation, the ryegrass population either remained high or steadily increased, even though ‘best practice’ herbicide and non-herbicide options were implemented.

All the diverse rotations made a large, and statistically significant, difference to the ryegrass seed bank over the three years. Even a one-in-three year break away from wheat, using the pasture legume serradella, was enough to reduce the ryegrass seed bank by over 50 per cent.

What is the benefit of adding a pasture phase?

In brief: Adding a pasture provides the opportunity to apply weed control tactics at stages during the season that are different to that typically used in grain crops.

The details: In a pasture phase of one, two, or three consecutive years, different tactics are used depending on whether the intention is to regenerate the pasture the following season.

In years where the pasture is grown for fodder and seed production, early-season interventions applied in isolation did little to suppress annual ryegrass (but were effective on barley grass and brome grass).

Season-long ‘excellent control’ and ‘glyphosate-free’ treatments decimated grass weed seed production whilst allowing high pasture biomass and seed production. The ‘excellent control’ treatment in serradella included tickle the soil in autumn, double knockdown, imazethapyr + propyzamide, clethodim + butroxydim (POST), spray-topping (paraquat), weed wipers (Roundup, MCPA (LVE), water, Logran, wetter).

Late season treatments implemented in the season where the pasture is terminated, such as brown manuring with glyphosate or spray-topping with tiafenacil (Terrad’or, Group 14[G]), are also very effective in reducing the seed bank of grassy weeds.

Can I expect other rotational benefits?

In brief: A boost in wheat yield is expected in the season after the pasture phase due to improved soil fertility and suppression of soil-borne pathogens such as nematodes.

The details: The final stage of this rotational trial is to measure wheat yield following the three-year rotation treatments. This assessment will occur at the end of the 2022 winter season.

In a separate pasture / crop rotational trial in Western Australia, also with investment from the GRDC, researchers from the CSIRO, Murdoch University and the Department of Primary Industries and Regional Development measured yield and protein content in wheat following serradella pasture at Ardath.

They concluded that serradella consistently boosted protein content in the following wheat crop without significantly affecting yield. This suggests that efficient pasture species like serradella, which fix nitrogen even in soils with some soil nitrogen present, can increase the value of the subsequent wheat crop through higher protein content.

GRDC Update paper April 2022 – Maximising crops and minimising weeds with smart phase farming   (Download PDF of GRDC Update paper)

GRDC Update paper March 2022 – Cereals after pasture legumes have higher grain protein levels

Related Articles

Related Articles

View all
Article
Ask an Expert

Can drones provide early warning of herbicide resistance?

Tristan Steventon, StevTech says ultra-high-resolution cameras on drones can rapidly map weeds for spray jobs and monitor changes over time. Read More...
Article
News

Cost-effective dual HWSC modes

Using two modes of harvest weed seed control can maximise the feed value for livestock and minimise the impact of burning chaff. Read More...
Article
News

Redefining fenceline weed control options

Some new herbicide registrations may help growers regain control and reduce the risk of herbicide-resistant weed seed moving into paddocks. Read More...

Webinars

View all
Video
Webinar

The economics of weeds — what they cost and the benefits of managing them effectively

In this webinar, we discuss the yield reduction weeds are responsible for and what a well-planned rotation for weed management can make a farming business. Read More...
Video
Webinar

Beating barley grass despite resistance and dormancy challenges

Learn how to control barley grass despite increasing dormancy and resistance challenges. Read More...
Video
Webinar

Can intercropping help with weed management?

Diverse rotations are a key aspect of the Big 6 and intercropping, despite its challenges, can provide opportunities for improving soils, weeds and risk management. Read More...

Videos

View all
Video
Webinar

The economics of weeds — what they cost and the benefits of managing them effectively

In this webinar, we discuss the yield reduction weeds are responsible for and what a well-planned rotation for weed management can make a farming business. Read More...
Video
Webinar

Beating barley grass despite resistance and dormancy challenges

Learn how to control barley grass despite increasing dormancy and resistance challenges. Read More...
Video
Webinar

Can intercropping help with weed management?

Diverse rotations are a key aspect of the Big 6 and intercropping, despite its challenges, can provide opportunities for improving soils, weeds and risk management. Read More...

Factsheets

View all
Fact Sheet

Control barley grass in LRZ farming systems

Barley grass in Southern and Western regions requires 3 to 4 years of seed set control to run down the weed seed bank. Read More...
Fact Sheet

Wild radish factsheet

Growers are adopting diverse and integrated control strategies to manage herbicide resistant wild radish populations. Read More...
Fact Sheet

Maximising crops and minimising weeds with smart phase farming

View the data from this research as presented at the GRDC Update (West) on 22 April 2022. Read More...

Subscribe to the WeedSmart Newsletter