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Lost top-soil a generational problem for farmers

Jane Ryan, Monday September 30, 2013 - 12:58 EST

An excessively wet August in northern Tasmania has farmers losing patience and a critical asset from their farms: top soil.

While drought has struck in the north of Australia, growers in the north of Tasmania are battling extremely wet conditions.

In parts of the state, rainfall averages ran two to three times their normal levels in August alone.

Crops have been planted late, or have yet to be sown, which means harvest will be pushed back by weeks next March.

While there are obvious losses to farmers from poor crops and a late or non-existent harvest, it's the hidden cost that they are being warned about.

Soil washed off properties into the neighbours place, dams, creeks or straight into the Bass Straight is a critical and long-term issue.

According to John McPhee from the Tasmanian Institute of Agricultural Research, soil takes a very, very long time to acquire and costs a lot to replace.

"It takes about 1,000 years to form about 20mm of soil," he said.

"So that's .02mm per year - you can't even measure it.

"One cubic metre of soil lost is .1mm - so if you lose one cubic metre of soil off your paddock you've just lost five years worth of soil formation," he said.

And one cubic metre is pretty easy to lose according to Mr McPhee.



"A reel which is 50mm deep, 200mm wide and 100 metres long - and there are many, many, many of them around at the moment - that's a cubic metre," he said.

"So if you've got 50 of them in your paddock you've just lost 50 cubic metres of soil.

"You're never going to get that soil back in your lifetime - probably not in your kids lifetime or your grandkids lifetime," he said.

Further to that, the cost of replacing the nutrients lost is about $15 per cubic metre - and that doesn't include the cost of transporting or laying it.

So how can this loss of productive soil be managed or prevented?

John McPhee works off a pretty simple method - but it needs to be implemented by Autumn at the latest.

"One of the first ones is to prevent run onto the paddock," he said.

"And that usually means drains - I mean there's no avoiding it.

"It's something most people try to avoid - it takes up land, it costs money to put in it costs money to maintain and they don't actually grow anything," he said.

"But at the end of the day you've got to think about well, what's the result do I want out the other end?"

Another important tactic for avoiding erosion is ground cover.

"So cover crops during the winter," Mr McPhee said.

Also within the paddock - drainage lines.



"So if you've got a place where water's going to run to any great degree put it down to a permanent grass drain," he said.

Mr McPhee acknowledges that again, most farmers don't favour grass drains, and for similar reasons: the cost of installing and maintaining as well as the loss of productive land.

But, he says, when they're used properly the results can be incredible.

Over the last five years, TIAR have managed to prevent a lot of erosion at one of their sites - and a very topographically tricky one at that.

"The first season it was put in, it was put in by eye," he said.

"The guy who did it was pretty damn good, but it wasn't quite right.

"With the guidance systems you have now we're able to do very accurate topographic maps and get very accurate drainage maps.

"We did that up there and put in a new drain in the second year, and honestly, the start of that drain was probably only five metres away from where the original one started, but the difference was just outstanding," he said.

Keeping tilling and traffic to a minimum also improves your chances of holding onto your topsoil according to Mr McPhee.

"Look, I work on a pretty simple philosophy - minimise the tillage, minimise the traffic," he said.

"Tillage and traffic are very destructive to soil structure.

"And soil structure is the guts of the issue," he said.

"How much water your soil's going to hold, and how much it's going to infiltrate."


- ABC

© ABC 2013

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