Turning compost by temperature


By Richard Mitchell

Farmers, municipalities and home gardeners alike understand the concept and value of composting but may not understand how to make good compost. The National Organic Program (NOP) offers guidelines for composting to eliminate pathogens and weed seeds. However, following these guidelines does not guarantee the creation of quality compost. To address this concern, composting research at Rodale Institute is geared towards developing methods that will produce quality compost and clarify some of the best practices to bring greater success in implementing the NOP guidelines.

Composting is the oxidative decomposition of a mix of organic materials. Oxygen is required to support the growth of beneficial organisms and to eliminate the risk of pathogens and other toxic compounds. Waste materials are blended together and then mixed on a regular basis to maintain proper oxygen levels throughout all parts of the pile. Because the oxygen is constantly being used up by the microorganisms that are breaking down the organic material and there is a limited volume of space between the material particles of the pile to hold oxygen, a compost pile must be turned many times to “re-fill” those in-pile spaces with oxygen. This turning process ensures that oxygen levels do not drop low enough to kill the good organisms and grow pathogens.

NOP guidelines require compost to be turned a minimum of five times within a 15-day period, during which time temperature must be maintained between 131- and 170-degrees F. While the guidelines act as a safety net to ensure pathogens are destroyed, they do not ensure that a diversity of beneficial organisms will be produced in the end product. In some cases, during the active phase of composting when organisms are using lots of oxygen, five turns in 15 days may not be enough to maintain proper oxygen for growing beneficial organisms. In other cases, the pile may not need to be turned as often as five times in the 15-day period.

This is a critical issue that may leave composters feeling uncertain. Instead of a general rule for turning, guidelines that help composters know exactly when the pile needs air would improve the end product. By observing biological indicators of compost activity in a pile a compost pile can be turned at the exact moment that the organisms need more air.

Establishing the research: May

Last May, as part of a research project funded by a Natural Resources Conservation Service Conservation Innovation Grant (NRCS-CIG), six piles were built on concrete pads to investigate issues with compost management according to the NOP guidelines. The piles were made out of identical materials: leaves as a carbon source, food waste as a green material, and chicken manure as a high nitrogen input. Three piles were managed according to NOP guidelines and the other three piles were managed by a process known as TAT (turn according to temperature).

The activity and growth of organisms produces vast amounts of heat and causes the temperature of a compost pile to rise quickly. This heat is essential to kill harmful pathogenic bacteria, fungi, protozoa, worms and other parasites as well as weed seeds in the pile, and it can also tell us when the pile needs to be turned. We use thermometers to measure the temperature of our compost piles as an indicator of the activity of the microorganisms in the piles. When a pile reaches 160 degrees F (or above) we then know it is time to turn the pile because high temperatures indicate that the activity of organisms is so high that the oxygen in the pile is being used up faster than it can diffuse into the pile from the outside air. This loss of oxygen, coupled with the high temperatures, can actually kill the good organisms if it isn’t addressed quickly enough.

The TAT piles were turned whenever temperatures reached this critical threshold, whereas the NOP piles were simply turned five times in 15 days (typically once every 3 days) as the guidelines suggests. Our goal was to investigate if turning according to temperature would result in a higher quality of compost with more beneficial microorganisms. We are also hoping to clarify whether the TAT method would allow the pile to be managed more easily than the NOP method, which requires mandatory turning but not always necessary or timely turning.

Concrete pads: The issue, the resolution

The design of the concrete pads used as platforms for our six compost piles caused quality issues in our end product. The design of the concrete pads inhibited mixing because the sides of the pads were angled slightly towards a drain at the center of the pad to allow any water leaching out of the pile to drain out into an underground holding tank for testing. As mentioned above, compost must be thoroughly mixed to maintain aerobic conditions, but the slight V-shape of the pads prevented proper aeration of a portion of the compost at the very bottom of the piles. Our flat-bladed compost turner was unable to reach those bottom-center materials, allowing that small portion of the pile to go anaerobic and generate pathogens. Even though harmful pathogens where destroyed throughout the rest of the piles, that small anaerobic portion of material at the bottom center was a continual source of pathogenic contamination for the rest of the pile.

The picture above illustrated the area of the concrete pads that could not be properly mixed and aerated. Properly aerated compost will be the brown color of 75% cocoa. Note how the color is dark black in the center of the concrete pad, indicating that the material became oxygen deprived and went anaerobic.

Luckily, the ability of the concrete pads to drain liquid was determined to be unnecessary which allowed us to resolve the turning issue easily. There was no liquid collected from the holding tanks below the concrete pads at any point during the process. This result illustrated another valuable aspect of making quality compost. A compost pile shouldn’t produce leachate if you’ve used a proper mixture of starting materials. It is absolutely necessary to use enough brown materials, such as leaves or woodchips, so moisture levels are managed properly. The brown materials also provide the piles with adequate structure to allow oxygen flow throughout. Too much wet waste material will cause the pile to become compacted due to lack of structure, preventing the circulation of oxygen.

Similarities in TAT and NOP piles: Actinobacteria

In both the NOP and the TAT piles, we ran into problems with the growth of actinobacteria. These bacteria are easily recognized as a powdery or ashy white growth that can show up in a compost pile with reduced oxygen. We determined that the standard compost recipe we used was too low in brown materials to deal with the quantity of food waste in the mix leading to the overgrowth of actinobacteria throughout the trial. Although we didn’t have enough food waste to create leachate, it was still too much for proper oxygenation.

When a pile isn’t turned frequently enough, or if the pile becomes matted down by too much food waste, the oxygen levels will decrease and these facultative anaerobic bacteria will take over. The problem is that actinobacteria suppress the growth of other beneficial organisms such as mycorrhizal fungi. Most agricultural soil is lacking a healthy fungal community and has too much bacteria to begin with. So adding heavily bacterial compost to a soil that already has plenty of bacteria doesn’t really benefit the soil microbial population, or result in improved plant growth. Ideally you’ll want to make compost very high in beneficial fungi so that you can begin correcting imbalances in your soil.

Differences in TAT and NOP piles: Actinobacteria

Visibly white-ish areas are actinobacteria.

At the end of the composting process we analyzed all six compost piles and found that, while all piles contained actinobacteria, the TAT piles had lower levels. By turning according to temperature we were able to introduce oxygen into the pile at the crucial times when oxygen levels where beginning to fall. Turning according to the NOP guidelines did not always coincide with the critical temperature window when oxygen was most needed in the pile.

Furthermore, the TAT piles only needed to be turned four times instead of 5 within the first 15 days. This demonstrates an interesting point. We were able to turn less often yet produce higher quality compost because we turned at the critical time when oxygen demands where highest.

Replicating the research: July

Our next step was to repeat the experiment in July by building six new compost piles. This time we decided to move the trial off the concrete pads so we could eliminate possible contamination. The six piles were built on level ground to ensure every inch was being aerated by our Global Repair Sittler1014 compost turner.

We also decided to make an adjustment to our compost recipe. We doubled the amount of leaves so our piles would have better structure and allow more airflow through the pile. We learned from our May piles that food waste can be very high in moisture and that there must be a substantially high amount of brown material in the pile to properly absorb and manage the moisture. We also suspected this new recipe would grow more beneficial organisms, specifically fungi. Since fungi live on logs, sticks, leaves and other woody material in the environment, we hoped that the extra leaves would help us make compost with higher numbers of fungi.

Beneficial fungi in a compost sample (400 magnification).

The management of the new compost piles was also slightly modified from the previous trial. As before, three piles were turned according to NOP guidelines and three piles were turned when temperatures reached 160-degrees F or higher. However, we decided to also turn the TAT piles whenever a significant amount of actinobacteria was visually apparent. We hypothesized that if the temperatures reached the critical threshold during the nighttime hours, depleting oxygen levels, then we would see the effects in the morning by looking for actinobacteria.

May versus July

Analysis of the data shows that the July NOP and TAT piles had significantly lower action bacteria and significantly higher fungi that the May NOP and TAT piles. This indicates that the adjusted compost recipe with higher amounts of leaves contributed greatly in solving the actinobacteria problem. The data also shows a trend of the May TAT piles having lower amounts of actinobacteria compared to the May NOP piles, suggesting that the TAT management practices may be beneficial in reducing these bacteria.

The data shows that there were slightly higher fungi levels in the NOP piles but this difference was not statistically significant. The numbers of fungi in all piles was still much lower than is needed to build better soil fungal populations and grow healthy plants.

We have learned that it may be possible to make quality compost by turning only at critical stages in the composting process exactly when the biological activity is reaching a crashing point, rather than turning a pile a prescribed number of times. We did discover, however, that actinobacteria may indicate that we have reached this turning threshold during the night when nobody is available to monitor temperature.

We have also demonstrated that the starting ingredients in the compost pile must be in the right balance to allow for proper moisture balance and adequate airflow. You must understand the nature of the waste resources you have and carefully plan out a recipe that will address potential problems later down the road. We quickly learned that much more leafy brown material is needed to compost wet food waste, which help with the in-pile dispersal of oxygen, the critical component to making compost.

Looking to next year

Next year we plan to build six more compost piles and repeat the experiment with the goal of finding more effective ways to promote fungal growth in the piles. This time we will be monitoring the temperature throughout the night, via a newly purchased recording thermometer, to determine if a correlation can be made between the visual appearance of actinobacteria and peaks in temperature at night. This will hopefully allow us to understand what is happening to the compost at night when nobody is watching. We can then determine better management strategies to mitigate problems that may occur.

We were able to reduce the problem with actinobacteria by adjusting our compost recipe to include more leaves. However, one problem that can’t be fixed so easily is the amount of garbage that can end up in compost made with food waste. Waste hauling companies are struggling to eliminate trash contamination, such as plastic bags and other non-compostable materials, so we have decided to use alternate waste materials for our green pile component until the contamination problem is solved.

Next year, instead of using food waste, we will use aged cow manure and rotten hay, which are both easily obtained farm waste products, and we will continue to use leaves because they are readily available. We predict that we will be able to further reduce actinobacteria and hopefully grow much more fungi when we make these adjustments.

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.

22 Responses to “Turning compost by temperature”

  1. Jeff Demers

    Thank you the above information. I own a small scale compost co. & predominatly compost wood shaving based horse manure in a mulch. I have recently sent samples to Rodale for testing. One was a shredded horse manure & the other was a leaf & horse manure mixture.
    My question is that I want to make a higher quality compost using these ingredience. I have the opportunity for food waste but I don’t know if I want to incorporate it. For the obvious reasons. But, if food waste can improve the quality of the compost I’ll introduce it. Or, could I make a great compost using the manure & just leaves?
    A big issue I have is that the bedding material, when broken down, still has a rough texture to it unlike a mature leaf compost. My customers have complaints about this. Eventhough the compost is very good, visual appearance is a tough sale. So many assume compost is soil like & are stuck on that.

    Any information is very helpful or, if I may, have the opportunity to speak with someone regarding my situation that would be a great opportunity also.

    Thank you,
    Jeff Demers
    203.748.6516

    Reply
    • Richard Mitchell

      Hello Jeff,

      You asked some very great questions.

      Compost recipe:

      Your compost recipe is missing one crucial component – green material. A standard compost recipe is five parts brown (high carbon), four parts green (hay, grass, food waste…etc.), and one part high nitrogen (manure, soy beans, blood meal, alfalfa…etc.). This is simply a guideline and must be adjusted for specific materials and end results.

      The food waste may be the missing (green) component to your recipe but there are also many other types of green materials you can use. Food waste has advantages and disadvantages. It is a good material because it is generated in large quantities and is readily available. You can actually get paid to take the stuff. Other materials such as hay may be harder to come by and can become expensive.

      Food waste, however, can lead to many problems (In our article we discussed some of the issues and have decided not to use food waste for our next round of compost). Food waste can arrive is a putrid anaerobic state, can have excess moisture (so you will need more dry martials to deal with this), may be contaminated with plastic… the list goes on. If you have a consistent, uncontaminated source of food waste, that is relatively fresh (not been sitting in containers for many days or weeks) then adding it to your compost is a great idea. You will have to experiment with the ratios of ingredients to produce a quality end product.

      Wood shavings in bedding material:

      Wood shavings can be a valuable component to a good compost recipe but must be dealt with properly. The high lignin content of the wood shavings will provide food for beneficial fungi. Shavings can also help provide structure and allow air to diffuse into the pile. This material, however, will take much longer to break down than other brown materials such as leaves because of its recalcitrant nature.
      The type of wood must be considered. Pine and other sappy/aromatic woods will take longer to break down than hard woods. The shavings may take years to break down. One option may be to let your compost age longer before selling the material. Over time, fungi will break down the material but only if there is fungi in the compost. If the compost is bacteria dominant the shavings may be present for a long time. Increasing fungi levels and species diversity will help your problem. You have the food source (wood shavings) to grow fungi so the next step will be to inoculate your compost piles with fungi.

      You can find great fungal inoculum in nature. High numbers and diversity of fungi are practically right under your feet. Look under logs, under the leaf layer in the forest, in old mulch piles…etc. and you will find white web-like mycelia (the vegetative part of a fungus). Another sign of fungi is the mushroom (the fruiting body of fungi). Collect small handfuls of fungal inoculum from many different sources (being careful not to disturb natural ecosystems) and add this material when you start composting. You can also inoculate woodchip piles with the material. The fungi will grow and multiply in the woodchips and will become large piles of inoculum for future use. The inoculum should always go through a thermal compost phase to insure pathogens are properly dealt with.

      Leaf material:

      A double edged sword? Brown leaves are a great carbon source for composting. They are dry and can serve to soak up moisture from food waste, they are easy to work with, and are also readily available. They also break down very quickly turning into a usable compost product in short time. The downside is that they become compacted as they break down. As leaves compact, oxygen diffusion to the center of the pile is reduced. The wood shavings from your horse bedding should provide structure which will help with this issue as long as they are fluffy and not the consistency of sawdust. Wood chips are chunkier and will add structure to a compost pile.

      I hope this information helps. Start with a basic recipe that includes more green materials and some fungi and make improvements from there.

      Happy composting.
      Richard

      Reply
  2. alexander mackay

    I am trying to get my pile to heat up in the winter. I have horse manure, old round bales of hay, food scrapes, leaves and cardboard. I started the pile by layering with hay, then cardboard , then manure and or food scrapes and leaves and then same one more time. I add to the pile every weekend with fresh horse manure and turn the pile.
    Any ideas on how to heat a plie in minus 10 weather?
    Thanks in advance.

    Reply
    • KJMClark

      “Any ideas on how to heat a pile in minus 10 weather?”

      Well, for one, I’d leave the cardboard out of the pile itself. *Very* high carbon there. But instead of putting the cardboard in the pile, put it on top. It’s great for insulation. Just remember to leave air gaps for oxygen to get in and waste gases to get out. Then do what you’re doing, but once it gets about 4′x4′x4′, start a new pile. Combine piles every now and then when they get smaller than about 4x4x4. And be sure to add water. Things get dry fast in the winter.

      Reply
    • Richard Mitchell

      Alexander, getting compost to heat up during the winter months can be tricky for small scale compost piles. It is best to start compost piles in a warmer building such as a greenhouse or a barn , and then move the piles outdoors when they are hot. Another option is to store the starting materials indoors so they don’t freeze. Lastly, make sure to use fresh not aged or leached manure.

      Reply
  3. Ben Cains

    For the question about composting in minus 10?
    This is just an idea but maybe have a greenhouse for composting. Another idea is to have the greenhouse connected to where you keep animals if you have any so that the heat that is generated is used to maintain the temperature in the greenhouse?

    Reply
    • Richard Mitchell

      Please be advised that composting in a greenhouse can have negative consequences if the recipe and management strategy is not carefully thought out. Putting large amounts of organic material together can result in large quantities of noxious gas (such as ammonia) being produced. Before composting indoors you should have experience making compost with those starting materials. Proper C:N ratio, structure, moisture and aeration is crucial. You should have developed a recipe and management strategy to keep the pile composting aerobically.

      Last winter we learned this lesson the hard way. A pile was built in our greenhouse with too much chicken manure. Within a few short days the green house was filled with ammonia and other noxious gasses killing all of the plants. The greenhouse workers reported that they were unable to enter the greenhouse until it was ventilated.

      A second pile was built with much less manure and no gas was produced. The pile was also managed more closely and turned more often to add oxygen to the pile. Always have a good idea of how your starting materials will react before composting indoors. Start with less nitrogen than you think you will need adding more if necessary. If you cannot commit to turning the pile frequently less nitrogen is a great idea. Also, build the pile with more structure (chunky materials) so the pile can breathe. Lastly, start with less moisture and add more if necessary. It’s much easier to add moisture than to remove moisture. Soaking your pile with water will limit the ability of oxygen to enter the pile resulting in anaerobic conditions (45-50% moisture is ideal).

      Reply
    • Max Smith

      Second that!

      I’m so excited about the questions you guys are asking and following through with + your in-season modifications to the original experimental designs. Inspiring stuff for young agrarians, really!

      Reply
  4. Norm

    [quote]
    Any ideas on how to heat a plie in minus 10 weather?
    [/quote]

    Lowering the C:N ratio will help make the pile heat faster. So use less “browns” or more “greens” or “manures.” Also, turning the pile mixes the components, which generally helps heating as well. Low moisture can be a reason for insufficient heating, as can lack of oxygen. While a greenhouse will definitely help, the cost is not justified just for the compost. If you do use a greenhouse, make sure it is adequately ventilated to draw in fresh air (oxygen) and vent out the CO2 and (hopefully not too much) ammonia.

    Happy composting,
    Norm

    Reply
  5. JohnS

    What was the reason of the low fungi level in all piles? If you have trouble to produce high level fungi what can a backyard composter expect?

    Reply
  6. Richard Hggins

    Regarding turning compost. As mentioned in my video’s on our web site, you only need to make the 1st turn at 14 days, and the 2nd turn at 30 days, then you can grow heat loving plants on it and at 90 days it is spread for all other crop types. Not only are you making an optimum soil conditioner you are producing a once only application of fertilizer!

    This solves the problem of modern day farm traffic, which in the latest British conferences is losing 20% of cultivable land in any one field due to the need for so many subsequent spray applications.

    I presented the Howard-Higgins System at the Soil Association’s National Soil Symposium in November and sold out of books too. There is no need for fallow or even green manuring! Needless to say the Soil Association want to visit my farm.

    I did a ten year study of the life and works of Sir Albert Howard and have developed technology that has no rival…..The world’s first Dog Waste composter for one.

    We provide practical teaching sessions as well as seminars on this revealing work.

    Reply
  7. Dwight

    Is your compost recipe available? I.E., number of front end loader buckets of chopped leaves to manure etc.
    Thanks

    Reply
  8. Richard Hggins

    Yes, it is available, and the majority of composters world-wide are missing out on several ingredients.
    Rodale Institute have been asking me ‘how do I make this kind of compost’

    I have suggested they get me over there to do a master class on the Howard-Higgins system.

    This system is gaining momentum in the UK and is going to Africa (Kenya) this spring.

    The science is available in the title The Lost Science of Organic Cultivation wherein it is shown how you can turn human effluent into a saleable fertilzer in 90 days.

    This is available from our web site
    http://www.suaglon.co.uk

    Sustainable Agriculture London.

    Reply
  9. Robert

    We have been using old/aged Sawdust for our Blueberries since 1979. We then started to take Woodchips, Leaves, Yard Waste, Horse Stable Maure ( which ends up being more Hay and shavings), & Grass Clippings. Food Waste has many issues/Regs and I have stayed away from it! All of this was being mixed/turned will front end loaders and I was able to buy a Good Used Pull type Compost Turner a few years ago. That has help us to make a better material to apply over our Farm to increase the organic matter levels in our already great soil. I just want to make it better before I go. This discussion is some of the best I have seen and I hope it continues. I am not organic, but use IPM and less Com. Fertilizer on my Farm. Still lots to learn! To Mr. Higgins, I am on a planning board for a great Mid-Atlantic Conf. and hope to contact you to see if we can get you over here to speak. Will pull up your web site to contact you.

    Reply
  10. boo hanson

    I’m a little late with my comment but would like to get feedback if I could.
    If you wanted to increase the fungal population of the compost pile, would spraying the pile while turning with a fungal dominated compost tea work? This seems to me that this idea would speed up the breakdown of the material a little faster. I use baby oatmeal to increase the fungii in the tea.
    Just an idea.

    Reply
  11. Jeanne Boucher

    To increase the fungal content of my compost, I include lots of branches and twigs when starting my 4 x 4′ pile. I break the branches into about 24″ to 30″ length, and add them as I’m layering my brown and green materials. This insures good air circulation throughout the pile and although I haven’t had the compost tested, I assume my compost will have a higher fungal content than it did before I started this practice. As I harvest the finished product, I screen off the branches and add them to my next pile. They are starting to rot and I’m thinking they are full of good fungi and bacteria. It’s interesting to observe how them deteriorate with each pile, until they are completely broken down.
    This year, I’m experimenting with bahia grass to produce my own mycorrhizal fungi.
    Jeanne

    Reply
  12. Melanie Lewis Ivey

    Richard:

    Have these data been published? If yes, can you send me the citation? If not, can you email me with the method(s) that were used to identify the actinobacteria that were present in the compost. I just had a grower contact me about “white fungus” growing in their compost and based on their description I suspect it is not fungal but bacterial. Kind Regards, Melanie

    Reply
  13. John

    Have you heard of a broad leaf weed killer that may be used by some alfalfa growers which, when eaten by horses or other animals, passes through the digestive system minimally affected thus causing killing or stunting of most vegetable crops grown in beds mulched by such manures or compost derived therefrom?? I am told that the only way to overcome the effect of this chemical is to allow the beds to remain fallow for 2-3 years while the sun and air break it down. Regards, John

    Reply
  14. Jordan Barnett

    The chemicals you are thinking of are called Aminopyralid/Clopyralid.
    Aminopyralid – sold as Milestone, Milestone VM, Milestone VM Plus, Chaparral, CleanWave, ForeFront, GrazonNext, Opensight and PasturAll) in the USA. Forefront, Pharaoh or Banish, in the UK.

    This chemical has a very long half life, some sources state times longer than 3 years, however it is encouraging that chemical is not broken down in a ruminants GI tract and therefore the chemical isn’t likely to have entered the human food chain – this chemical kills or sickens any broadleaf plants it comes into contact with.

    New guidelines state that the chemical must not be used on grass being cut for hay, therefore preventing this problem in the future, in the UK at least.

    In the Vale of Evesham, UK, vegetable growers who use too much Round up but wish to drill a crop often add ground charcoal to the soil, it has colloids that allow for the adsorption of the chemicals. Then the field is free of dangerous levels of Round up and the farmer can drill a crop. Perhaps you could try this approach?

    Hope this helps,
    Jordan Barnett – 2nd Year Horticulture Student

    Reply
  15. Robert Qualls

    An excellent idea to monitor the relative abundance of Actinobacteria and fungi, particularly with respect to temperature and oxygen concentration.

    Just a comment: most Actinobacteria (such as those formerly Actinomycetes) are strictly aerobic and have been recognized as important in degrading lignin and promoting the formation of humic substances. I would think that Actinobacteria are one of the best bacteria to foster in compost piles.
    Here is a research method that I use to measure oxygen concentration inside compost piles: stick PVC poles with lots of holes drilled into the into pipe into the heap. Put a stopper in the top. The gas inside will diffuse and equilibrate with the compost pore space gases. When a sufficient time has passed., stick a dissolved oxygen probe down into the pipe and you can get an accurate measurement of the oxygen concentration. This is a standard method in soil research (Methods in Wetland Biogeochemistry, DeLaune et al., 2013, Soil Science Society of America). Then you really know when the pile is going anaerobic. Oxygen probes can be expensive but there are some relatively cheap ones.

    Robert Qualls
    University of Nevada, Reno NV

    Reply
  16. Louise Edmonds

    Hi there

    I was wondering if you might be able to tell me the make of the compost thermometer you are using and where it can be bought?

    I live in Western Australia so an online supplier won;ld be great.

    Thanks

    Louise

    Reply

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