Old techniques revived to fight weed resistance

31 Mar, 2011 04:00 AM
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Stuart Smart
Stuart Smart

IN A state where 90 per cent of grain growers practice minimum till, turning over the top 30 centimetres of soil may seem almost blasphemous.

But Stuart Smart is convinced it has enormous potential for managing weeds and the non-wetting soil on his property at Mingenew, Western Australia.

This season Stuart started using a mouldboard plough, after watching with interest a series of trials run by Peter Newman of the Department of Agriculture and Food (DAFWA), who is funded by the Grains Research and Development Corporation (GRDC) for much of his research into weed management.

The mouldboard plough is still widely used in the United Kingdom and Russia on certain soil types. By turning the top 30 centimetres upside down, it buries dry matter, green matter and, most importantly, weed seeds. It also brings the clay-based soil to the top where the moisture is available for newly sown crops.

Stuart’s property, Erregulla Plains, comprises of yellow sand, coarse pale brown sand through to sand over gravel, which have clay content between 10 and 30 per cent . Average rainfall is 380mm.

The property is 22,000 hectare and Stuart’s now cropping 12-14,000 hectares a year. He also runs 12,000 Dorper breeding ewes, which are run on the non-arable areas and utilise the stubbles after harvest.

“This is still very much an experiment, there is very little information on how to turn this type of soil sucsesfully so we are on a very steep learning curve” Stuart said.

“We have to make sure the soil’s wet enough that the sand doesn’t spill back into the last furrow rather than being buried, but we’re starting to work out how to manage that.

“It’s taken several attempts to get the sowing right, and it will be interesting to see how each technique impacts yield and quality at harvest.

“When we first started with an air-hoe drill it was getting bogged in the soil, which ends up feeling as fluffy as fresh snow after the plough’s been across it. Using coil packers stopped that, but the air-hoe was still bringing up the soil we wanted to stay deep.

“We’ve swapped to using an air seeder and following it with a coil packer to help to prevent wind erosion, which is the biggest concern when you’re exposing the soil like that.

“Barley’s the best crop because you get some cover in a week to ten days which helps to hold the soil together. Wheat’s not too bad, but we can’t put lupins in paddocks that have been ploughed.”

Managing the weed seedbank is one of the key reasons Stuart has turned to the mouldboard plough. Ryegrass and wild radish are the biggest problem on his place and he’s keen to reduce the need for chemicals and help to prevent resistance.

“Previously, we’ve had land out of cereal production for up to six years to make sure we killed any resistant ryegrass, and were paying up to $80 per hectare for chemicals on the hard to kill populations.

“Burying the seed so deep stops it germinating and so far there’s not a weed in sight on the paddocks which have been ploughed – so they’re back in production straight away.

“We deep-rip our soils anyway, so would have had that expense anyway. Overall, I think we’ll come out in front in terms of both labour and costs by preventing the need for chemical spraying for several years,” Stuart said.

Ryegrass seeds are believed to survive 2-5 years in the soil, and wild radish about 8 years.

Stuart’s plan is to use the mouldboard plough on about ten per cent of his cropping area each year, so each paddock would have a ten year cycle of weed seed burial.

DAFWA’s Peter Newman says the key to success is to use the practice in the right places, and his research has been aimed at identifying the soil types where the technique will work best.

“We’ve tested mouldboard ploughing across eight sandplain soil sites over three growing seasons.

“While the impact on yield has been mixed, and some other factors have been at play, on average the ploughed paddocks yielded an additional 320 kg/ha for a range of crop types.

“The great news is that average weed control has been 94 per cent, and some sites have been completely weed free for several years after ploughing,” Peter said.

The ideal sandplain soils, according to Peter’s research, are made up of wettable topsoil, with a good pH profile (no acidity), no subsoil compaction and good water and nutrient holding capacity.

Stuart Smart’s still waiting to see the results on his property, but a month after sowing there was not a weed in sight.

He believes the practice does complement the minimum till techniques he uses nine years out of ten in each paddock.

“The soil is fragile so you have to take care and minimum till is important, but I think there are times when you simply have to move the soil.

“We take an integrated, holistic approach aimed at achieving sustainable, profitable farming using a minimum of chemicals, and I’m always keen to add another string to the bow.

“If we get the results that means mouldboard ploughing, then I’m all for it,” Stuart said.

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