During the past decade, growers in low-rainfall zones such as the Victorian Mallee have begun to embrace pulses as more than just the occasional break crop.

But soil variability and undulating sand hills make it riskier to plant pulses other than lupins, and low biomass can increase the potential for wind erosion to occur during dry times.

Research trials found the practice of deep ripping can lead to significant yield and profitability benefits in cereal crops grown on sandy soils, so researchers are now exploring whether that is also the case for pulses.

Frontier Farming Systems research agronomist Michael Moodie says there have been remarkable results from small-plot trials on sandy soils.

“Loosening the soil profile by deep ripping or other mechanisms – spading or whatever you choose to use – is having a real, positive effect on how that pulse crop grows,” he says.

“And the production gains have been substantial. We have seen, on average across a range of trials and a range of seasons, basically a 0.5-tonne-per-hectare benefit in lentils, and most of the other pulse crops have seen around a 1t/ha benefit. That’s how much we are closing the yield gap on those particular soil types.”

Mallee growers attend an on-farm field day demonstrating the benefits of deep ripping for legumes. Photo: Michael Moodie

Chickpea yields across six Mallee trial sites increased by an average of 1.1t/ha, field peas 1t/ha, faba beans 0.9t/ha, vetch 0.7t/ha and lentils 0.5t/ha.

Mr Moodie says the monetary gains from addressing constraints such as high penetration resistance are significant, and he urges growers to consider the value of pulse crops as a profitable part of the rotation, not just as a weed or disease break.

Boosting barley yields by 0.5 to 1t/ha might put $200/ha extra in the pocket, but a 0.5t/ha increase in lentil yields could improve the bottom line by as much as $300 to $400/ha, he says.

Then there are the added benefits for nitrogen fixation from growing crops with more biomass.

A trial at Tempy last year found yields in chickpeas increased 1t/ha after deep ripping. Follow-up research near Ouyen this year measuring water use and water use efficiency (WUE) in chickpeas will test whether variety and time of sowing have any impact on responses to ripping.

Another trial in progress is investigating whether deep ripping affects the efficacy and crop safety of pre-emergent herbicides such as fomesafen, terbuthylazine and metribuzin when applied before lentils on sandy soil.

A landscape-scale trial set up last year at Kooloonong to evaluate barley response to deep ripping across multiple soil types is this year being used to measure the response of chickpeas in the second year after ripping. A section also has been re-ripped for comparison.

Mr Moodie says once deep ripping was applied at larger sites, the benefits were lessened because of variability in soil types. There were also questions about the effectiveness of ripping done last year when conditions were dry.

“There’s a few things going on there,” he says. “It’s a work in progress. The next step is seeing what happens when we scale it out to different soil types.”

Potential issues

A concern for many growers is whether deep ripping makes soil more fragile and following it with pulse crops that do not produce sturdy stubble would increase the risk of erosion.

“A few people are hesitant to rip in front of pulses for that reason,” he says. “But then there also are quite a few farmers who are doing it.”

Mr Moodie says he is looking for ways to help growers overcome that unease and better understand that it is possible to conserve soil and maintain ground cover by ripping in the right conditions and using the right types of rippers.

Growers making the choice to deep rip or ameliorate soil were looking for productivity improvements across several seasons, not just in the cereal or pulse phase.

The only real question was whether they were confident putting the legumes first. “Some people are deciding it’s far too risky,” he says. “They are going to rip, go in with a crop like barley and then follow with the legume later. Other people are saying that the benefits they are seeing in the legumes are far more profitable than what can be achieved in a cereal crop, so they’re willing to take that risk. The decision to rip or not is irrespective of whether you’re going to grow a legume crop – it’s how you use that legume crop in the rotation.”

But deep ripping is not as simple as running a machine through a field and going back to business as usual.

Potential adverse effects include trafficability issues, excessive soil throw, poor seed placement and crop damage caused by inadequate separation from pre-emergent herbicides. For these reasons, and the absence of a response to ripping, lupins should not be sown in the first season post-ripping.

Risk mitigation methods

Mr Moodie says rolling post-ripping can reconsolidate the surface soil and improve flotation, while implementing full or partial controlled-traffic farming (CTF) and not ripping where machinery will pass also helps, especially in lentils.

He recommends ripping in the right conditions, when there is some moisture in the soil, but not when it is bone dry or too wet, ensuring there is good stubble cover over these areas and disturbing it as little as possible.

Slower sowing speed and using wider press wheels can reduce the risk of excessive soil throw into the crop row and collapse of the furrow side wall.

“Thinking about some of the risks of sowing into soft soils, it’s important to be really careful with pre-emergent herbicides to the point where you might forgo pre-emergent herbicides in that first year after ripping,” he says.

“But then you need to have a backup option for what’s going to happen if you have weeds. Do you grow a Clearfield crop in that circumstance? That is where pulse crops can come in, with options to control grass weeds with in-crop grass-selectives. So that’s a good thing.”

Grower testimony

Piangil grower Mark Kentish, who has been using CTF since 2016, has followed Mr Moodie’s research projects across the Victorian and South Australian Mallee with interest.

Mark produces cereals, canola and pulses and brown manure crops across a range of soil types, from deep sands to sandy loam, limey heavy flats and sheet limestone.

We saw some really good responses on chickpeas in that first year.

After seeing a neighbour get good results from deep ripping, he and a friend – who also operates on 12.2-metre CTF  – bought a ripper together.

The hard pan layer in the sand seems to be at a depth of about 300 to 350 millimetres, so the ripper was set for 400 to 450mm, and followed by a heavy steel roller to flatten the rough soil surface for better seeding depth control with an NDF disc planter.

Mark says the first ripping of paddocks with deep sand in 2020 generated biomass and yield  responses in legumes, apart from lupins, but no noticeable difference in cereals.

“We saw some really good responses on chickpeas in that first year,” he says. “The second year we concentrated more on paddocks planned to rotate to legumes and did not see much of a response. I think it’s because we were so dry, and there was no moisture there at depth. Plus, because it was hard pulling that year, the ripping maybe didn’t get as deep as we should have.”

Mark says the long-term average annual rainfall in his area is about 300mm, but there had been a run of very dry years since 2018, when just 190mm was recorded.

With a record 97mm in April contributing to a rainfall tally of 256mm by the end of August, Mark says the deep-ripped crops are now able to access moisture and nutrients at depth. “This year, we’re seeing a good response in the legumes,” he  says.

“This is the first time I’ve had field peas on deep-ripped country and it’s just nice and even from the flats to the hills and, normally, even with this much rain, you wouldn’t necessarily see the peas grow that well on the sand.

“The paddock trials aren’t perfect but but the differences are stark, especially with the chickpeas, we’re seeing a lot better growth on those in that deep sand where chickpeas used to underperform.

“And in the past three or four weeks, we’re seeing a very good response in the paddock that was ameliorated, had chickpeas brown manured  then sown to wheat. It’s really taken off.”

The trials are being conducted as part of GRDC’s investment in southern pulse agronomy through Agriculture Victoria.