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Critical steps for producing the best farm compost

More farmers are trying composting, but their questions indicate that some have been disappointed with the results, says a composting researcher at Alberta Agriculture, Food and Rural Development's AgTech Centre in Lethbridge.

"Composting can be a very beneficial way to turn potential waste into a useable product, but only if it's done properly," says Virginia Nelson, of the AgTech Centre. "I've seen the results of unsuccessful composting. Product that should have turned into compost, rotted instead."

Using aerobic decomposition, which means "in the presence of oxygen," composting in a windrow turns manure into a valuable resource by breaking it down into a humus-like product that can be applied as a soil amendment. The compost has less odour than raw manure and producers can benefit from its nutrient value.

A suitable carbon to nitrogen ratio is step one for successful composting, says Nelson. Adding a carbon amendment helps keep beneficial levels of nitrogen in the manure, because the nitrogen bonds to the carbon, which prevents it being lost to the atmosphere in the form of ammonia.

"The starting material's carbon-to-nitrogen ratio should be 25:1, or at the most, 30:1," says Nelson. "If producers don't have the right ratio, they need to add a carbon amendment, such as straw or untreated sawdust."

The right moisture content is also an important part of that first step. "Material planned for composting should have an initial moisture content of 50 to 60 percent. If it's above that, it needs to be dried out before composting begins," she says.

Moisture content needs to be closely monitored during the active composting phase. A 55 percent moisture content is key to maintaining valuable microbial activity in the composting pile.

"Any more than 55 percent moisture and oxygen will be forced out of the pile, which will kill the micro-organisms responsible for the composting process," says Nelson. "But, any less moisture than that and those same micro-organisms won't be able to move throughout the whole pile. The composting process would then slow down or stop completely."

Temperature is the other main criteria that requires close monitoring. This, too, relates to maintaining microbial activity in the composting pile.

"Monitoring temperature helps reveal if something else is wrong in the windrow," says Nelson. "Microbial activity in the composting windrow generally raises the temperature to between 40 and 60° C. But, if the temperature rises and then suddenly drops, it probably means a lack of oxygen or a lack of moisture has killed the micro-organisms and the process has stopped. Turning the windrow frequently to aerate it will help keep oxygen at the level needed by the micro-organisms."

The active composting phase has ended when the windrow is turned, but the temperature doesn't rise, says Nelson. The length of time that takes varies depending on the material being composted. The curing phase follows, during which producers need to let the compost rest until it reaches ambient temperature, generally about three months.

While these steps lead to successful composting, producers need to be aware there may be restrictions on the sale of compost. It's not enough to simply monitor temperature and moisture levels, says Nelson. Alberta, for example, has formal regulations for making compost that is a legal sellable product.

AgTech Centre is part of the Alberta Agriculture, Food and Rural Development Agricultural Engineering Branch and has expanded its mandate to include all aspects of agricultural sustainability.

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