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Wetland weeds to farm compost: everyone’s a winner

A floating excavator pushes weeds towards the bank so the terrestial excavator can pile them up to dry.

Compost made from harvested water weeds improves soil health on local farms

JAMIE Jurgens approaches one of several large compost piles spaced out across his Bowen farm, scoops up a handful of rich crumbly dark earth, and inhales deeply.

“This is ready to spread on my green beans,” he said.

“You can tell because there’s no bad aroma. It just smells of soil. The cool temperature and the texture are also good indicators.”

It has taken three months to get to this point, and the pile has been turned approximately 10 times.

“It’s important to turn compost regularly and add moisture because the organisms breaking it down need oxygen, water and food just like we do,” he said.

“While they are working, they use energy and generate heat – like when you go for a run.

“It really doesn’t matter what materials you start with, as long as you adhere to the composting process and you end up with a black soil.

“It could be bagasse, green waste, anything.”

This compost is unusual because it’s made from an invasive weed that had been choking a nearby wetland – and posing a threat to wildlife.

The scheme to harvest the weeds from Kalamia Creek, Ayr, and transform them into a natural soil conditioner was delivered through a partnership between NQ Dry Tropics and Evolution Mining.

NQ Dry Tropics Senior Project Officer Scott Fry (left) with Bowen vegetable grower Jamie Jurgens.

Dead weeds (on the left), becomes nutrient-rich compost

The aim was to restore the creek to good health while boosting local agriculture.

Jamie said he didn’t hesitate to join.

“I got involved with this project because I agree with the concept,” he said.

“The weeds in these waterways are doing a job naturally by harvesting all of the minerals and nutrients in the water.

“If it came off the land, it makes sense to me to put it back on the land.

“Compared with synthetic fertiliser, the carbon and nutrients contained in compost are a lot more stable in the soil, so they’re less likely to leach out of paddocks and into waterways.

“That means they are more available for our crops, making them healthier.

“It’s a win-win.

“I just don’t see the sense in paying money for chemicals when there’s a more natural process available.

“We have noticed a lot less nutrients running off our farm since we started using compost, that’s for sure.”

A new approach to weed control

Scott Fry has been battling the spread of invasive weeds in local wetlands for nearly 10 years, alongside groups including the Burdekin Shire Council, Lower Burdekin Water and local farmers.

The Senior Project Officer at NQ Dry Tropics said species such as cumbungi and water hyacinth damaged valuable habitat, and required ongoing management.

“Traditionally Kalamia Creek would have been teeming with mangrove jack and barramundi, and providing food for a wide range of migratory birds,” he said.

“However, constant weed outbreaks have sent fish numbers plummeting by physically preventing them from migrating between freshwater wetlands and the sea to breed.

“When kept under control, the weeds can actually be beneficial because they filter water and prevent nutrients and sediment from flowing downstream.”

But, without control, they quickly grow to cover the creek surface, removing oxygen from the water.

Preparing to spread the compost on a newly-planted crop of beans.

Weeds left on the bank of Kalamia Creek to dry.

If they’re left to die and decompose, oxygen levels deplete further, leading to fish kills during hot weather.

Things get worse when the rains arrive and flush the putrid water downstream towards internationally-significant wetlands and the Great Barrier Reef lagoon.

“The key is to harvest them regularly and keep the waterways open,” Scott said.

“In the past, our budget only stretched to mechanical removal, and we simply left them on the bank.

“It’s exciting that for the first time we have funding to take things to the next level by turning them into an organic, renewable compost.”

Once the weeds have been removed by an excavator, they are left on the bank to drain, reducing their weight prior to relocation.

Following strict biosecurity checks to ensure no viable seeds remain, they are loaded onto trucks and transported to local farms.

With the pilot project coming to an end, Scott believes there is plenty of scope to streamline the operation and make it more cost-effective.

“This has been a great start and we’ve had a lot of interest from local farmers,” he said.

“Continued investment would help us find ways to make the process cheaper and more efficient.

“Turning these weeds into a marketable product could help us offset the ongoing cost of managing them.”

Jamie agrees.

“The next challenge is finding more efficient ways of harvesting them and getting them to the trucks,” he said.

“We have a lot of great heads in our industry, and I’m sure that if we put them together, we’ll come up with something.

“I think there’s a positive future for what we’re doing.”

Rows of compost ready to be delivered to the farm.

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