Friday, March 29, 2024

Winning with wetlands

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Treatment wetlands might be a winning solution for farmers to reduce their farm’s environmental footprint and meet future nutrient limits set by regional councils without having to change their farm system.
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Owl Farm, the St Peter’s School-Lincoln University demonstration dairy farm at Cambridge, is investing in a treatment wetland to reduce nitrogen losses from the farm.

Water monitor wells would be installed to test nitrogen levels of water flowing into and exiting the wetland to determine the nitrogen extraction effectiveness of the wetland and to aid in improving wetland performance.

On some farms, well-constructed treatment wetlands could reduce nitrogen leaching by up to 70%, Opus environmental services manager Roger MacGibbon says.

A well-designed wetland worked to convert nitrate to atmospheric nitrogen by a bacterial process called denitrification.

It could also trap sediment and phosphorus and reduce the release of faecal bacteria into water bodies.

A treatment wetland could be an extremely effective tool, but it had to be on point, MacGibbon said.

“If it’s not done right it could just become one big duck pond.”

Every farm had variables, including hydrology, climate, topography and soil type, which needed to be considered.

The location of the treatment pond was crucial as well as the types of plants selected, which would vary depending on the region.

The maintenance of a wetland to maintain optimum performance and make sure it didn’t become over-grown was also important, he said.

The construction of the wetland at St Peters is planned for February with planting in spring.

If it could achieve a 50-60% reduction in nitrogen leaching it would significantly improve the farm’s nutrient budget, Owl Farm demonstration manager Doug Dibley said.

About 45ha would drain to the 0.7ha wetland, equivalent to 30% of the milking platform.

If it reduced the nitrogen leaching by just 50% from that area, it could reduce the overall farm leaching from 33kg N/ha to about 28kg N/ha, he said.

“If that was achievable that would be a success. If it is only 20%, in this environment it might not be a good investment. That’s the value of what we are doing – if it doesn’t work we will be the first to say.”

The direction regional councils were going with nutrient limits meant farmers had to be as profitable as they could be within future set regulations, he said.

The $55,000 wetland plus monitoring costs were being jointly funded by Waikato River Authority, Waikato Regional Council, Opus and St Peters. St Peters would be responsible for the cost of maintenance and upkeep of the wetland, and monitoring.

“We have skin in the game. We are a commercial farm like all others, we don’t have a bottomless pit – everything we do has to be commercially viable,” Dibley said.

A lot of farmers would resist spending that money themselves on treatment wetlands until they saw more data, which was what the project was about, he said.

The payback on the investment could be more profitable than the other current options, which included reducing cow numbers, reducing nitrogen fertiliser or building a feedpad – all options that impacted on production or came with a hefty capital cost.

“It’s another option farmers may have up their sleeves if they become restricted with nitrogen limits under new regional council regulations.

“It’s about trying to provide an alternative option to manage some of the environmental impacts.”

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