Composting barns to allay public fears

Speaking at the recent Centre for Dairy Excellence Dairy Barns conference in Timaru, Woodford said dairy farmers will have to do “something” to get cows off pasture in late autumn and winter.

The New Zealand community will not allow current dairy practices to continue for the next 20 to 30 years, he said. However, there are various types of dairy barns and no one answer for all.

“I am enthusiastic about composting barns and the solutions they can to provide in NZ, but they are not the only solution of course.”

Woodford said he has found one composting barn that is working well in NZ but there may be as many as three others, and “a couple of hundred” in the US.

He identified four basic barn farming systems: 24/7 indoor farming with year-round milking and fully cut-and-carry feeding; indoor-outdoor hybrid with year-round milking; indoor-outdoor with seasonal milking; and off-paddock shelter used only for limited periods of bad weather in a seasonal milking operation.

He also identified four basic barn types: composting; freestall barns with separate standing areas and individual bedding stalls; non-composting loafing barns; and slatted-floor barns with effluent bunkers underneath.

On his analysis, only composting barns tick all the boxes as suitable and economic for all four farming systems.

A fully composting barn has large areas of composting material at least 600mm deep where the cows spend virtually all their time.

“It will have roof venting and daily tilling. If those things aren’t occurring then it is not going to be a composting barn.”

The compost should stay in for 12 months. If it has to be pulled out sooner because it is turning into a foul-smelling “anaerobic custard” then the farmer is doing something wrong, said Woodford.

“It’s got to smell nice. It’s got to be pretty dry. If you can squeeze water out of it or anything like that, it ain’t compost.

“There’ll be steam everywhere as you till, because evaporation is where the moisture goes.”

There has to be some form of waterproof sealing under the 600mm compost, with a drainage system to catch any effluent, although in a properly functioning composting barn nothing will come out.

“All your moisture is going up through the system to the sky. But it won’t work without the right structure -- a decent-shaped roof of at least 18 degrees [slope]. You’ve got to have internal venting up the top and you’ve got to have daily tilling.”

The compost is tilled by tractor twice a day, usually when the cows are out being milked. However, tilling also works with robot milking systems in which the cows do not leave the barn.

“That’s OK. The cows will get up and get out of the way as you do it. I’ve seen that happening in North America.

“I’ve seen one of these systems in Oregon working nicely with a robot system. That particular one is interesting because they have a freestall barn and a composting barn they put in later. The cows have a choice as to where they go and most of the cows prefer to walk past the freestall and around into the composting barn.”

Woodford said benefits of composting barns include cow comfort -- “cows love them” -- clean udders, less lameness than with freestall, and no liquid waste.

They may also mitigate nitrogen leaching and greenhouse gas emissions, although that needs quantification. That should come with improved biological efficiency, as measured by the ratio of milk produced per kilo of bodyweight.

Woodford said farmers should be aiming for a minimum of 1.1kg of MS/year/kg liveweight, or an average across the herd of at least 1.2.

“There’s no doubt you can do better than 1.2. The very best pasture farms are probably around 1.1 and there might be some claiming to be closer to 1.2. But with barn farming we can go beyond that. You really can get very big increases in production from these systems.”

Emphasising that a composting system will not be for everyone, Woodford said it is a matter of matching the barn structure to the farming system, but he warned that systems could change over time and there is no simple answer as to whether it is the structure or the system that comes first.

“I’ve concentrated on composting because that is the exciting one that a lot of you wouldn’t know anything about,” Woodford said.

“I’m confident this is going to have a role for us in NZ. We are going to have to do something to get cows off-paddock in the second half of autumn and winter.

“If we think the community is going to allow us to stick with [our current systems] for the next 20 to 30 years, that’s not going to happen.”

However, one critical questioner from the floor of the conference said that while composting had emotional merit, “economically, I can’t make it work”.

He questioned the cost of the necessary sealed layer under the compost; ongoing costs in acquiring compostable material such as sawmill waste at a time when sawmills were increasingly using it themselves; possible costs in storing material before and after composting; and problems with fungus and dust.