Multi-species cover cropping key to soil health

Nuffield scholar finds multi-species cover cropping benefits for soil


Grower Stories
Aa

Expanding cover cropping to include more species may be a pathway to healthier soils.

Aa
Alex Nixon, pictured with sons Archie, left, and Eddie, right, intends to look after his land to the best of his ability. PHOTO Supplied

Alex Nixon, pictured with sons Archie, left, and Eddie, right, intends to look after his land to the best of his ability. PHOTO Supplied

In a bid to improve soil health and boost water infiltration, Queensland grain grower Alex Nixon has been trialling multi-species cover cropping on his 8500-hectare property on the Western Downs.

The trials follow his GRDC-supported Nuffield Scholarship in 2017, when Alex researched sustainable farm management practices from North Carolina in the United States to Overbury in the United Kingdom.

He found that cover cropping - in particular, multi-species cover cropping - can greatly increase soil health.

"We get a decent rainfall here - up to 600 millimetres annually," he says.

"But we only collect about 25 per cent of that in soil. I've always felt we could do better."

A desire to improve soil health also plays into another long-term goal - keeping the land productive for the next generation.

"I don't want to degrade the land any further," he says.

"I am fortunate enough to be a custodian of some of what I consider to be the best land going, thanks to the endeavours of my mum and my late dad.

"I intend to look after this dirt as best I can to afford the same opportunities to my sons."

Farming operation

Alex, his mother Robyn and brother Tom, farm at the historic Queensland Hereford stud 'Devon Court'.

I am fortunate enough to be a custodian of some of what I consider to be the best land going, thanks to the endeavours of my mum and my late dad. - Queensland grower Alex Nixon

Tom looks after the stud, while Alex manages the cropping on 2600ha.

About 40 per cent is devoted to wheat and barley, 20 per cent to chickpeas, 20 per cent to sorghum and the remainder to long-fallow cover cropping.

Alex says his Nuffield journey began with the intention of researching ways to improve soil carbon.

"But the information I found uncovered much more than that," he says.

"What my studies have taught me is that soil is complex. Looking at improving just one element is futile.

"So, total soil health quickly became the focus of my research, through mimicking nature's fine balancing act."

His research led him to US field trials in North Carolina. Those trials showed that several consecutive years of cover cropping had allowed organic matter to build up significantly.

"The residue from the crops slowly breaks down, providing food for microbes and boosting soil retention, acting like a mulch," Alex says.

Although Australian cover cropping has mostly concentrated on using just one species (such as millet, oats, pulses or sorghum), he found that multi-species cover cropping is more beneficial.

"Single-species cover crops do enhance ground cover, but by adding even one or two different species into a cover crop the microbial activity can be greatly enhanced, boosting the diversity of the soil ecosystem," he says.

On-farm example

For the past three years, Alex has been experimenting with multi-species cover cropping on some of his long-fallow paddocks.

While implementing diverse cover crops can pose initial economic issues, the long-term environmental and economic benefits outweigh any initial costs. - Queensland grower Alex Nixon

"My advice to others would be to start small and consider the frequency and size of cover rotations based on the benefits they can produce," he says.

His first trial was implemented during the long-fallow period after a sorghum crop.

It consisted of predominantly millets, grain and forage sorghum, corn, sunflowers and pastures, such as lablab.

"And some pumpkin - a last-minute decision to see what would happen," Alex says.

The main goal is to build ground cover and harbour natural soil biology."

Protecting the soil surface from harsh Australian conditions also increases water storage by minimising evaporation.

"The different species of plants add various biological elements, as different microbes are drawn to different root systems," Alex says.

"We found that the following wheat crop, planted into the cover crop residue, out-yielded the standard long-fallow area by about 0.2 tonnes per hectare, and was far more consistent.

"The NDVI (normalised difference vegetation index) satellite image of the paddock also showed that the cover crop area obtained much denser biomass production."

After growing the cover crop for 75 days, it was sprayed out. The next crop was planted directly through the residue, with Alex noting increased moisture through the cover-cropped area.

Challenges

Alex Nixon's first multi-species cover crop, pictured, contained eight species. The following wheat crop yielded 0.2 tonnes per hectare more than standard long-fallow paddocks. PHOTO Supplied

Alex Nixon's first multi-species cover crop, pictured, contained eight species. The following wheat crop yielded 0.2 tonnes per hectare more than standard long-fallow paddocks. PHOTO Supplied

As part of his research, Alex explored the viability of multi-species cover cropping being adopted in Australia, but found a number of barriers.

"Upfront costs can be an issue. Cover crop seed is very expensive, as is the investment required for machinery or contract sowing," he says.

"Visiting farms in the US and England, it was clear that the initial cover-cropping season can result in some financial deficits.

"At Overbury Farms in England, long-term soil conservation had been prioritised over the short-term bank balance and lower income was being supplemented with other revenue streams.

"While implementing diverse cover crops can pose initial economic issues, the long-term environmental and economic benefits outweigh any initial costs."

Improvements in soil health, for example, could see fertiliser and chemicals costs decrease, while boosting yields.

Cover cropping could also open alternative revenue streams through grazing or agistment.

"It may be costly to get it going, but 100 per cent ground cover in harsh conditions will capture rainfall and decrease evaporation," Alex says.

Learning curve

Alex is keen to point out that he is still learning about multi-species cover cropping and how it will work on-farm.

"I don't have all the answers, but I'm keen to experiment with what I've learnt and seen around the world," he says.

"I do think that with careful management, multi-species cover cropping is a viable option for Australian broadacre farmers seeking to improve soil health and preserve the landscape for generations to come."

Grower story: Water infiltration in North Carolina

JRH Grain Farms in North Carolina was a tour highlight for Alex.

Water infiltration there - via increased soil organic matter (SOM) - has risen because of multi-species cover cropping.

The 320ha farm grows non-genetically modified varieties of corn and soybeans, white wheat, black oats, triticale and barley, as well as pasture-fed animals including cattle, sheep and pigs.

Alex says their initial decision to grow three cover crop species was made to reduce erosion and winter weeds.

"However, with the following cash crop season, they noticed many subsequent benefits, such as nutrient cycling, reduced fertiliser and herbicide requirements, weed suppression, increased brix levels (linked to plant health) and reduced insecticide use," he says.

The farm continued to increase cover cropping to 11 species and now boasts SOM levels of more than five per cent, Alex says.

Increased SOM and cover cropping's protective layer has also led to higher water infiltration and moisture retention, allowing the farm to optimise water storage capacity within the soil and capitalise on local high rainfall levels (1168mm annual average).

Alex says SOM acts as a sponge and research shows it can hold more than its own weight in water.

"Research has shown that a one per cent increase in soil organic matter means the soil can hold an extra 71,920 litres per acre - a remarkably significant increase," he says.

More information: Alex Nixon, aanixon@live.com.au, 0429 432 467

Aa