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Windrow composting systems can be feasable, cost effective (Research Brief #20)

Posted June 1996

One of the things we were interested in was how to implement a composting system without changing a farmer’s existing setup. — Bill Connolly, UW-River Falls

Windrow composting can help farmers manage dairy wastes economically, according to a study sponsored by the Center for Integrated Agricultural Systems (CIAS).

Researchers from the University of Wisconsin-River Falls calculated the costs of various composting systems that use either specialized composting machinery or common farm equipment and compared this to existing research on the economics of long-term manure storage systems. Their research suggests composting can spare farmers from expensive long-term storage systems that require high structure and upkeep costs, especially if farmers are willing to share compost equipment or use existing farm machinery.

Bob Butler, of the UW-RF agricultural engineering technology department, Bill Connolly, assistant director of the UW-RF research farm, and Vern Elefson, a UW-RF ag economist, estimated composting costs by measuring the labor required and by calculating equipment and operating costs for four composting methods. Butler said the cost analysis may be useful to farmers who are thinking of switching to composting rather than investing in long-term liquid or solid storage systems.

“We wanted to look at composting for small to medium dairy farms,” says Connolly. “Not much was being done for these farmers to help with manure management.”

Windrow composting

Composting using the windrow method requires some management to set up windrow piles, turn them periodically, and monitor the composting process. Compost forms as microbes in the manure decompose the organic wastes. Since this method requires a moist environment containing oxygen, farmers must aerate the material by turning the piles two to four times during the process.

The researchers estimated the costs of managing compost piles that were 50 feet long, 12 feet wide, and 3 feet high, using manure and bedding from the UW-RF farm. The team considered four scenarios for composting: investing in a tractor-drawn compost turner; hiring custom help with a compost turner; using an existing front-end loader; and renting a bulldozer.

The team examined both the labor costs of composting and the equipment investment for a 60-cow dairy farm. They based these values on an economics model developed by Brian Holmes of the UW-Madison ag engineering department, and Rick Klemme, a CIAS ag economist. This format allowed the River Falls researchers to compare the economics of composting to several other manure management methods, from daily haul to higher-investment, long-term storage systems.

Estimating the costs of composting

  • Time required. In their on-farm demonstration, the researchers measured several elements of composting time management, including the time required to form the windrow pile (loading, traveling, and unloading time using a tractor and manure spreader); the time needed to turn the pile for the first time and for subsequent times (using either a compost turner and tractor, a front-end loader, or a bulldozer); and the time required to reload the compost (using a tractor, spreader, and front-end loader). When calculating the time required, the researchers assumed two turnings were adequate for the compost turner methods, while four turnings were necessary for the bulldozer and front-end loader methods.The researchers estimated that the time required to form the windrow pile takes about 6.8 minutes per ton of manure, with 20 minutes’ setup time. The time needed to turn the piles for the first time varies, depending on the equipment used. A bulldozer takes the least time at 0.2 minutes per ton, followed by the compost turner at 0.8 minutes per ton, and the front-end loader at 1.5 minutes per ton. Although the bulldozer takes the least amount of time to turn the piles, this method is also the least efficient and requires more turning times, the researchers found.Additional turnings require about half the time compared to the first turning. Again, the researchers found the bulldozer was the quickest method, followed by the compost turner and the front-end loader. Reloading the compost for field spreading using a tractor/spreader/front-end loader combination took about 2.2 minutes per ton, with about 20 minutes for setup.
  • Annual operating costs. Based on these time estimates, the researchers calculated annual operating costs for each composting method, including electricity and fuel, labor (at $5/hour), annual land cost for the compost site (for 2.1 acres), and costs of straw to mix with the manure (at $2,450 per year for 60-cows at 4 pounds/cow/day). The bulldozer method required an additional $1,420 annually for renting equipment, while custom hire using a compost turner required $3,055 (for labor at $65/hour). Annual operating costs per cow were the lowest for the front-end loader and the bulldozer methods at $142/cow each, followed by the custom-hire compost turner scenario at $170/cow, and investing in a compost turner at $185/cow.
  • Equipment costs. The researchers estimated equipment costs for composting. Regardless of the method, composting requires about a $12,600 equipment investment for using a tractor (calculated by assuming 40 percent of its use is loading and hauling) and for buying a solid manure spreader, based on a 60-cow farm. Composting using a turner and tractor requires another $16,600 equipment investment, for a total of $29,200. The front end loader requires an additional $2,750 investment (for costs of a front-end loader at 15 percent of its use), for a total investment of $15,350. Using a bulldozer or hiring custom help with a compost turner would require no additional equipment investment beyond the $12,600 tractor and spreader costs, according to the study.The total investment costs per cow are $487/cow for the compost turner, $256/cow for the front-end loader, and $210/cow for both the bulldozer and custom hire compost turner methods.

Although compost turner methods require the highest investment, they are also the most efficient way to make compost. Farmers who share equipment or hire custom help could significantly reduce this investment. Using a front-end loader or bulldozer would require little, if any, additional equipment investment, although these methods would require more windrow turning.

Composting compared to other methods

How do composting costs stack up against other methods of managing manure? Figure 1 compares the total investment and annual ownership and operating costs of four composting scenarios, compared to four other manure management systems: a high-investment above-ground concrete tank, a picket dam, a remote stacking slab, and daily haul methods.

Figure
1: Cost comparisons of seven manure handling methods
Type Invest-
ment/cow
Annual

cost/cow

Concrete* $1,426 $266
Picket dam* $1,030 $194
Remote slab* $697 $148
Tractor turner (compost) $487 $185
Front end loader
(compost)
$256 $142
Bulldozer (compost) $210 $142
Tractor turner
(custom hire)
$210 $170
Daily haul* $150 $54
*Data from
“The economics of dairy cow manure long-term storage,” by Richard
Klemme and Brian Holmes; other data, UW-RF study; all data based on
60-cow herd.

Figure 1 shows that the total investment for composting methods are between those of daily haul (at $150/cow) and a remote stacking slab (at $697/cow). Composting costs are far below high-investment systems, such as a concrete tank system. Annual costs of composting are similar to those of remote slab methods (at $148/cow) and picket dam (at $194/cow), according to Figure 1.

The feasibility of composting

These analyses suggest that composting can be economically viable for managing manure, especially if farmers use existing equipment, rent machinery, or hire custom help.

Using a front-end loader or renting a bulldozer would lower the investment costs of composting. Although these methods don’t turn the compost piles as efficiently as a compost turner, they would not require drastic changes on the farm. “One of the things we were interested in was how to implement a composting system without changing a farmer’s existing set-up,” says Connolly.

Another option is to invest in a compost turner or hire custom help to run a turner. Several farmers could share the $15,000 cost of a compost turner. “I see this as a potentially cooperative effort where four or six farmers would share equipment costs,” says Connolly.

The type of manure management system a farmer chooses depends on the farmer’s goals and needs, Butler said. Farmers should consider the size of their herd, whether land and labor are available for composting, and what type of system they are currently using. “It doesn’t pay for farmers who’ve already invested in long-term storage methods to switch to composting,” says Butler, “but if farmers are already using daily haul or have a short-term storage system, it may be easy to switch to composting.”

In this way, a farmer can keep manure management costs reasonable and still gain some of the benefits of composting, such as fertilizer value, ease of handling, and soil amendment.

In other CIAS-sponsored research, Butler’s group has shown that compost may have long-term benefits to the soil and the health of the environment by preventing nutrient runoff. Composting may also fit more easily into a farmer’s lifestyle. These benefits of composting are hard to put a price tag on, but should weigh into a decision to compost.

Butler says composting will require some commitment, but he doesn’t expect farmers will have to make drastic changes. “There’s certainly a middle ground,” he said. “If a farmer wanted to get some of the benefits of composting like reducing nitrate runoff and producing a good product for the fields, it would be feasible to use just a front end loader, without the full blown operation. For anyone getting into expensive liquid management systems, it might pay to switch to composting.”

Contact CIAS for more information on this research.

Published as Research Brief #20
June, 1996