Composting barns for production livestock is not a hugely new concept and has been used in wetter dairy environments, including the Pacific Northwest, for some years.
Typically, a barn system will comprise of an 800mm to one-metre deep bark-type material, which becomes self-composting as animal effluent, urine and air mix into a dry bedding material that farmers can get a season’s use out of before scraping it off and applying it to the land to help lift soil organic matter over time.
Nelson firm Wholesale Landscapes is also finding increasing interest from Kiwi dairy farmers who are grappling with the complexities of water quality management and greenhouse gas (GHG) emissions, and looking to adjust their farming systems to better manage these.
For many the challenge is to try and contain those emissions and losses, but the cost of systems that could capture both, like completely enclosed barns, is significant.
They may also detract from the ‘free range, grass-fed’ image that is starting to resonate so well with overseas consumers.
Marketing manager Tom Filmer says for some farmers a more cost-effective compromise is an open-sided barn system allowing good air circulation, while also providing the compostable surface for cows to sit and lie on post-grazing.
Wholesale Landscapes currently has several farmer clients in the upper South Island utilising the company’s bedding shavings and is also involved in trials in Canterbury in its early stages.
“Typically, they will work to a base of about 700-800mm deep of wood material and this will get ripped, often on a daily basis to keep it aerated, and stop it from matting up and the composting process stalling, turning it smelly and wet,” Filmer said.
“It does need to be managed, it is a bacterial process.”
At the end of the season the material is dug out and can be spread via a muck spreader onto paddocks due to be cultivated as additional organic matter.
Filmer says the company has its own methodology for collecting the trash material left post-harvest, but the demand from foresters for the company to come and collect it was growing.
“More forestry companies say they want to do better (with forest residue). Everyone knows about what happened at Tolaga Bay, and the risk of it happening again is something many want to avoid,” he said.
The value of forest residue is also on an upward trajectory as technology and demand develops for using the material as a coal replacement for industry fuel.
Other uses are also developing, including as a biofilter media in wastewater management systems.
Work by Waikato University professor Louis Schipper has shown agricultural water quality can be improved through denitrification to treat subsurface drainage water on farms.
This can be achieved using denitrifying bioreactors – large trenches dug between farm paddocks as outlets from drains or drainage tile.
These get filled with wood chips, in turn colonised by bacteria from surrounding soil, with the water routed through the trenches.
As the bacteria consume the carbon in the wood chips they absorb the nitrate in the water, reducing nitrogen levels between 15-90%.
The suitability of compostable systems for New Zealand dairy farms has also been touted by Lincoln University honorary professor of agri-food systems Professor Keith Woodford.
He first came across the systems in Oregon, and could see the suitability for NZ’s similar higher rainfall climate.
He follows a Waikato family, the Allcocks, who are into their seventh season using the composting barn approach with their Te Awamutu dairy herd.
Called a cow “mootel” by the family seeking cow-friendly housing, the compost bedding became an unexpected bonus from the system, something to be added to paddocks once the season has ended.
The nitrogen bound within the compost can be released at a rate the paddocks can absorb, rather than the dump received during in-paddock urination.
Woodford says the warmer bedding environment for the cows means less energy consumption to stay warm, while pastures recover quicker with the cows off the paddock.
Filmer says Wholesale Landscapes enjoys being part of a rapidly developing concept where thinking is moving to a more circular approach to resources like wood.
“We are working resourcefully and collectively to solve a couple of big problems for two big industries,” he said.
