Rock crushing project at Conmurra Station hopes to double carrying capacity on shallow soils

Now with the big jump in rural land prices, heavy machinery is once again rolling in some paddocks across the region, this time transforming some of the least productive farming land into high performing country.

One of the most ambitious projects is at Conmurra Station, between Kingston SE and Millicent, where Nick and Katherine McBride are close to completing the first 240 hectares of about 1012ha of shallow soils with rocky outcrops they plan on tackling in the next few years.

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Since early January, their 2020 D11 CAT bulldozer with a single tyne ripper has been ripping to a depth of one metre.

Mount Benson-based contractor Andy Murdock, Murdock Rock Crushing and his team have been following behind with a D8 pulling a 30 tonne roller and levelling bars.

After three passes, any large boulders have been crushed to a size where a Fendt 500 hp tractor towing a 2.4 metre wide FAE225D rock crusher - more commonly used to build roads - can crush the rock further.

Once repastured, the McBrides hope to be able to more than double the carrying capacity of these paddocks from about 9DSE/ha to 20DSE/ha.

"These flats we are working on have been described as 'weekend soil' because 'they're too wet on Friday and too dry on Monday'," Mr McBride said.

The idea that these flats could be considerably more productive was evident more than 30 years ago when a D7 ripped down the Princes Highway to lay a telephone line towards Robe. That one metre wide strip is green year-round on shallow soils.

Since then, they have ripped 2ha with a D9 and in the late 1990s they did another 8ha with a D10.

"It was expensive, hard going and brought up a lot of rock, which ended up at the Kingston groyne but the 20 acres (8ha) we did for $5000 grew much more feed, was always green and the sheep liked to camp out there," Mr McBride said.

With strong livestock prices and the tax incentives available, the McBrides decided it made economic sense to tackle a larger area.

After looking at several machines they bought the CAT D11 from Japan which had 300 hours on it for $3 million, excluding GST.

Their exit strategy was to sell the bulldozer after the first year if they couldn't keep the earth works within a $2000/acre to $3000/acre or $4940/ha to $7413/ha budget but this looking very achievable.

There have been some challenges along the way with the rock beneath their paddocks some of the hardest limestone in the region. According to tests it varies from 40-80 megapascals.

In comparison house cement foundations have a strength of 25MPA.

The McBrides say their main dozer driver Lee Sutherland has done a fantastic job but Mrs McBride said it was a challenge on the hills where they were replacing the metal boot on the ripper nearly daily.

Luckily back on the flats, where the water table is only 70cm below the surface, the tyne is ripping in the water keeping the metal cooler. In these areas they have only had to replace the boot every five to seven days.

Mrs McBride says several other areas of the project have been better than they expected, including the fuel economy of the D11, which is using about 105 litres an hour.

"We were unclear of how many acres we would be achieved a day but at 1.25ac (3ha) an hour it has come in well under the worst case scenario," she said.

"Another thing adding up to a positive result was that Andy thought he would need to do six passes with the roller and leveling bar but now he is only doing three, as the 57-tonne on each track destroys most of the rock problem when it goes over one half of the previous rip line."

The McBrides estimate the final costs of the ripping and munching are about $4940/ha and - while this equates to $5m across the earmarked 1012ha - they see it as an investment for future generations at Conmurra, including their son Phillip, who is working as a mechanic at CAT Adelaide.

They also plan on contracting out their D11 to other producers, if the opportunity arises.

"We benchmark our returns per DSE and if things (commodity prices) stay where they are and the management stays in tune we will be in front in less than 10 years at 20DSE/ha," Mr McBride said.

Once the earthworks are complete in a couple of weeks, the McBrides will sow permanent pastures, which will be largely chicory and clover based.

Contractor Andry Murdock knows first-hand the benefits, having transformed about 100 hectares of his own shallow limestone country at West Avenue.

"There are places which would always go brown on the first hot day in September but now are staying green to the end of the year," he said.

"On dryland paddocks which normally only run 3-4 DSE/ha, once we had ripped the paddocks and sown them down to chicory, lucerne and clovers, in the first year we were able to carry 45 lambs a hectare from September to the end of January."

He says cracking the surface rock enables the water to move down into the soil profile instead of sitting on the surface during winter.

In the past three years, his FAE225HD has completed more than 3000 hours - both locally and down to Mount Schank near Mount Gambier. Most of this has been between January and March each year.

Mr Murdock says there is growing interest as land values have "gone through the roof", making the costs of $1600/hectare to $2470/ha (depending on how hard the rock is) economically attractive.

"Most farmers will start with 50 to 100ac (20-40ha), which is a budget that most find achievable so in 10 years they have 1000ac (404ha) that have doubled in production and because it is pasture renovation it is a 100pc tax write off," he said. "Once you have done (rock crushing) once, it is done forever."

Conmurra is Mr Murdock's biggest single project to date and while it has been slow going at 0.8 kilometres an hour, he is pleased with the results. He has also bought a second rock crusher to speed up the process.

"We could be going to six inches (150 millimetres) and going nearly twice the speed but then there is more surface rock - eight inches (200mm deep) is the sweet spot," he said.

"At the surface the rock is like gravel and the rocks which are golf ball or tennis ball size tend to be four to six inches (100-150mm) down."