Cutting-edge compost

By Troy Hinke

 National Organic Program (NOP) regulations require certified organic compost to be turned five times in 15 days. The assumption is that temperatures will remain above 130-degrees F long enough to kill pathogens and weed seeds and give you a finished product in the end. But research has shown this doesn’t always happen. With very little detail on when and how to turn within that 15 day period, composters can end up turning too often or not turning enough for their pile. Turning too often can interrupt the heating-up process, causing temperatures to drop. Not turning enough can lead to an overheated pile (over 165-degrees F), depleting the oxygen and making the pile anaerobic.

Researchers working on the project titled “Demonstration of Improved Compost Management to Effectively Utilize Animal Waste Nutrient Resources and Support Increased Soil Nutrient Retention” are studying a technique that relies more heavily on monitoring temperatures to determine when and how to turn the pile or windrow. The goal is to develop a much more efficient system that saves time, energy and money, and yields a finished product faster.

A different kind of compost

Practices that follow current NOP guidelines commonly generate temperatures that remain above 145-degrees F for months, creating an inhospitable environment for most of the beneficial organisms in the pile. When such piles remain hot for long periods, the oxygen content of the pile becomes very limiting, killing beneficial fungi, protozoa and nematodes that are vital to cycle and retain key crop nutrients within the pile.

This research will demonstrate a different composting approach, where time of turning is based on a temperature ceiling of 160-degrees F to ensure that the pile does not reach extremely high temperatures. This practice allows oxygen to remain in aerobic ranges during the entire composting process, causing cooling and finishing to occur more rapidly and without need for excessive turning.

The innovative essence of the temperature-related composting regime is its ability to support and enhance the balance of aerobic bacteria, fungi, protozoa and nematodes within the compost mix—biota that are vital to improve nutrient cycling and retention.  Coupling the turning of compost with precise temperatures reduces the amount of turning needed to properly manage the pile and keeps the oxygen content of the pile high enough to support a better-balanced, active biotic community. The more active biotic community speeds the composting process and stabilizes its carbon and nutrients more quickly.

The setup

To begin the research, two 50-ton compost piles were constructed in November of 2011 at Rodale Institute. The piles were made up of brown leaves, food waste and chicken manure. One pile was managed according to NOP guidelines; the other pile was managed according to the temperature-related turning regime. The projected outcome was that the NOP pile would stay at a higher temperature for a long period of time, while the temperature-related turning pile would return to ambient temperatures much faster.

Initial observations

As with much research, what one expects to happen doesn’t always and surprises often lead to more poignant revelations. Contrary to our hypothesis, the pile that was managed according to NOP regulations stayed above 131-degrees F for exactly 15 days. It came down in temperature very slowly, returning to ambient temperature close to two months after starting the composting process. The pile that followed the temperature-related turning regime remained above 131-degrees F for 33 days, returning to ambient temperature a little over three months after starting the composting process.

After reaching ambient temperatures, both compost piles were assessed with a microscope for the microorganisms present. Tilled soil and soil to which synthetic chemicals have been applied often have an unbalanced bacteria-to-fungi ratio in favor of the bacteria. The hope was that there would be a high fungal content in the temperature-related turning compost pile, if not both piles, so an application of the compost would begin to return balance to the soil. The results, unfortunately, showed that each pile was bacterial-dominant. Due to the temperatures being high for so long, it is most likely that the compost piles lost oxygen and created an anaerobic environment. As stated earlier, this results in the loss of beneficial fungi, nematodes, and protozoan. These were shown to be lacking in the microscope analysis of the compost.

Next steps

The compost from these piles was spread on the neighboring dairy farm in a field to be used as a cow pasture. The rates of application were one ton per acre and ten tons per acre for each of the composts (NOP and temperature-related turn). Lysimeters were installed in the plots where the compost was applied. The lysimeters will collect rainwater percolating through the soil, allowing us to assess the levels of compost-applied nutrients that may leach through the plow layer.

Six new 50-ton compost piles were recently started atop the concrete pads at Rodale Institute. As before, three piles are being managed according to NOP regulations and three piles are following the temperature-related turning management practice. These piles are being monitored daily for temperature and moisture levels, and the data are being collected. After reaching ambient temperatures, the microbiology of these piles will be assessed using a microscope. We are, again, hoping to end up with a high fungal content in one or both of these compost piles. Results from this year should begin to reveal whether last year’s initial flip-flop of expectations was a relevant trend or a seasonal fluke.

If this research proves the new method of composting to provide more beneficial compost, it would mean big things for compost producers everywhere. Less turning would be required per pile, which means less labor. The compost piles would also finish the composting process in a shorter period of time. This means that more compost is able to be produced in the same amount of time, which in turn provides more revenue for the producer/seller. On top of these benefits, the compost will provide the life that many soils have been missing.

This material is based upon work supported by the Natural Resources Conservation Service, U.S. Department of Agriculture, under Grant Agreement Number 69-2D37-11-499. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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