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Chemical residue adds layer of complexity to legume production

Wade and Chad Nickolls in a paddock of PBA Highland XT lentils at Pinnaroo, South Australia.
Photo: Danielle Nickolls


  • Owners: Wade, Danielle and Chad Nickolls
  • Location: Pinnaroo, South Australia
  • Farm size: 7200 hectares, owned and leased
  • Annual average rainfall: 330 millimetres
  • Soil types: sandy loam over clay, heavy textured clay loam over clay, white non-wetting sand, pH 5 to 7.5
  • Enterprise mix: dryland broadacre cropping
  • Crop program (2020): 55 per cent cereals, 15 per cent canola and 30 per cent legumes
  • Typical rotation: Lentils/wheat/oaten hay.

Vetch has been a staple in the rotation of third-generation grain grower Jeff Nickolls since he began producing it during the 1990s on the family farm south of Pinnaroo, near the South Australia–Victoria border.

A versatile multi-purpose crop suitable for grazing and hay, vetch copes well with a wide range of soil types and conditions. But Jeff’s sons Wade and Chad, who now operate the farm, noticed it was not doing so well in some places. The vetch would germinate vigorously before going into a decline as though it was “growing in a bowl of salt water”.

“It stays green and growing but it just doesn’t grow the vegetative growth so it can grow grain at the end of the year,” Wade says. “It comes up looking really good then it slowly gets worse and worse. When there’s damage like that you won’t get the bulk and it just doesn’t turn to yield either.”

Investigation showed the crop had been affected by residue from Lontrel™ (clopyralid) used several years earlier for controlling broadleaf weeds, such as volunteer lentils and vetch, and skeleton weed or cape weed in cereals and canola.

Wade says they are aware of the plant-back period of six to 12 months for the Group I herbicide and avoid sowing susceptible crops in the following year. But the combination of hostile sandy soils and very low summer rainfall in most years since 2012 has reduced residue breakdown and pushed out the carryover period, even when low-to-moderate herbicide rates are used.

“We are very careful,” Wade says. “Usually you don’t get caught for the whole paddock. You’ll get caught in a portion of the paddock, in a soil type that you don’t quite understand. We’ve got to be looking out two or three years ahead now, which is quite disappointing. It just makes farming more complex. It means you have to lengthen your rotations; you can’t put legumes where you want to all the time and you’re getting to the stage where choices are being taken away.”

Wade estimates 20 per cent of the farm is at risk, but not every year. In some years – such as 2019 when less than 10 millimetres of rain was recorded in the first four months – the impacts were felt across 10 to 15 per cent of the cropped area.

“There’s nothing you can do,” he says. “Once it goes like that you’ve just got to put up with it. We still harvest, it’s just really bad. This year we’ve hardly got any though, only two to three per cent, because we’re very wary of it now.”

Soil mapping a useful tool

Soil mapping has helped the Nickolls brothers identify some – but not all – areas where chemical residue is more likely to cause problems. They also have a clay delving and spreading program to address sandy soil constraints and try to smooth out some of the variability within paddocks.

“You’re always guessing a little bit,” Wade says. “Basically, you’ve got to learn each year from it. We might have to deep rip a paddock before we can try and grow legumes again. It’s not massive, we can manage it, but it’s annoying because you’re getting caught for years.”

The solution? Wade says a two or three-pronged approach is needed: one that combines more cost-effective non-residual chemicals and better-performing varieties with greater tolerance to Lontrel™ (clopyralid) as well as Group C chemicals such as metribuzin. Group C chemicals used pre and post-seeding cause similar damage to legumes – especially lentils – on the sandier soil types.

Some current and emerging varieties have tolerance, but do not yield well enough for growers to seriously consider swapping over to them. There are also issues with chemical registration and market acceptance, which Wade says GRDC is examining.

“I am looking at some trials on our place and it’s really good to see,” Wade says. “The varieties are getting better, but they’re still probably only 80 per cent of the yield of the conventional varieties with no damage and no residue. That 20 per cent is where our profit is.”

Vetch may have given them more than its fair share of grief, but it’s not the only legume crop Nickolls Partners has grown. Jeff also introduced field peas in the 1990s and lentils in about 1998. Wade recalls they dropped lentils after three years because the varieties were not suited to the area.

After converting the entire farm to no-till by 2002, they returned to lentils in 2005. By then varieties had improved and the family was running a semi-controlled-traffic program, except in their hay paddocks.

Wade NickollsWade Nickolls with chickpea seed at his Pinnaroo property. Photo: Danielle Nickolls

Wade says they do not have a standard rotation, preferring to remain flexible and base crop choice on soil nutrient levels – they test regularly for nitrogen, phosphorus and sulfur – and the spectrum of problem weeds in an individual paddock.

“We’re harvesting a lot more grain from the cereals,” he says. “So, we need to be putting nitrogen back in. As lentils and some of the other legumes have become more profitable for us, we’ve had to tighten up our rotations, as in having more legumes in the program, so there’s definitely no set rotation. Growing wheat on wheat on wheat would be very simple really, but it’s just not achievable.”

Wade says they still apply significant volumes of fertiliser in the cereal phase, especially when it follows lentils, which have shown themselves efficient at producing enough nitrogen for their own use but do not leave a lot behind for the next year.

There was a massive swing towards lentils as the region’s growers rushed to take advantage of high prices and new varieties that were more suited to lower-rainfall zones. But fluctuating prices and a downward price trend in the past two years have taken some of the heat out of the market.

“Less than half the lentils are grown here compared to five years ago because of the price,” Wade says. “I think most people are getting a bit of a steady rotation. There’s still a portion of field peas and beans and there’s still lupins on the sandy country, which is pretty important to a lot of people.”

Discussion group helps

Wade says being a member of the Pinnaroo Pulse Check discussion group, established in 2017 as part of the Southern Pulse Extension project, has been “really thought-provoking”. Regardless of whether growers were growing their first or 20th legume crop, he says the exchange of ideas is healthy and helpful.

“Everyone’s using different agronomists, so you’re not all doing the exact same and you can pick and choose a bit and challenge your own agronomist,” he says.

“The other thing is, we don’t just talk about lentils, we’re talking about beans, chickpeas and other things we’ve tried and gone away from and whether we should go back to them. The plant breeders need a pat on the back, because the varieties are getting better, they’re listening and they’re getting things through quicker that are going to help us.”

Wade says he and Chad have previously tried growing chickpeas but found them more susceptible to disease and less reliable for yield than lentils. They grow lupins most years and know they can grow a “beautiful stand of faba beans”, which can handle frost but not hot wind at flowering.

To be honest, if we could grow a bean, it would be really good because I’d love to swap it up between beans and lentils,” he says. “And if we can have a profitable bean that we could harvest a decent crop off each year? That’s on the wish list.”

More information: Wade Nickolls,

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