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AgTech Centre tests best windrow turners for top quality compost

Compost windrow turners are the lynchpins of quality compost production, yet they are also the most costly component to purchase and operate. To help producers choose the right compost turner for their operations, the AgTech Centre in Lethbridge, Alta. tested seven turners for their ability to produce high quality compost.

“Windrow turners are vital to the composting process because they help optimize the temperature, oxygen and moisture levels of the compost windrow,” says Virginia Nelson, AgTech Centre Manure Management Project Co-ordinator. “Turners release excess heat that can build up from microbial activity and provide oxygen to promote that activity. Without the proper conditions, the micro-organisms that are consuming the oxygen and breaking down the manure will die.”

Tests were conducted over three years at five sites with multiple compost windrows in southern Alberta. The following models were tested: a standard front-end loader, Allu SM 2-12 bucket, Scat 481, Wildcat FX700, Aeromaster PT-120, Earthsaver CT-12-PTO and Brown Bear PTO PA35-10.5. The Aeromaster, Earthsaver, Wildcat and Brown Bear turners are what are known as drum-style turners. Drum-style turners make up 90 percent of the turners used in agricultural composting. With the exception of the front-end loader, all the turners tested were specifically designed for compost windrow turning.

Nelson and her team tested each unit for horsepower requirements, compost mass and volume reduction, nutrients retained, organic matter retained, compost temperature as well as other biological and mechanical efficiencies.

“All six compost windrow turners produced high-quality compost,” says Nelson. “In general, the compost was coffee coloured and the texture was similar to a loam or potting soil.”

The only device tested that did not produce high quality compost was the regular front-end loader. “Turning compost with a regular front-end loader found on most farms will produce compost of sufficient quality if the goal of producers is to spread it on their own land,” she says. “But if a producer wants top quality compost to market, then a turner built specifically for compost management is required.”

The horsepower (hp) required to turn the compost varied considerably. The Brown Bear, averaging just under 100 hp to operate, required the most horsepower because its saw-tooth paddle auger system lifts, turns and moves the entire windrow, says Nelson.

The Aeromaster required the least horsepower, averaging just under 40 hp to operate. “It turns the entire windrow, but it has a simple, efficient mechanical system,” she says.

Other tuners, such as the Scat and the Wildcat, turned half of the windrow at a time, generally using half of the hp than the models that turned the entire windrow at once, she says.

While the Aeromaster required the least horsepower to operate, it also made the quickest work of the compost windrows, moving the most tonnes per hour. The Allu SM 2-12 bucket turned the least tonnage per hour.

Beyond quality, one of the most important selling points of composting for producers is mass reduction. In this crucial factor, all the turners did well. For example, the Brown Bear, Aeromaster and the Earthsaver all promoted mass reductions of around 30 percent. “With a properly controlled composting system, producers can realize consistent mass reductions independent of the turner used,” she says. “Additionally, volume reduction in most cases amounted to around 40 percent.”

Organic matter content was relatively high in the compost produced by the turners except for the front-end loader. “The front-end loader doesn’t break up clumps of material as well, leaving little organic matter in those clumps at the end of the process,” she said.

Final organic matter percentages are not yet in, but Nelson says the Brown Bear, Aeromaster and the Earthsaver achieved high organic matter levels, averaging an estimated 60 percent organic matter content.

When choosing a windrow turner, Nelson recommends producers first do their homework. “Decide what you want to use it for, take a look at all the available options and the costs you are willing to incur,” she says.

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