Manure Manager

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Manure Minute: Troubleshooting your compost pile

May 27, 2022  by Chryseid Modderman, University of Minnesota Extension

Proper composting is almost an art, and it takes the right combination of many components to work efficiently. In general, you want a particle size of one-eighth to two inches; internal temperature of 110 to 150F; moisture content of 50 to 60 percent; oxygen content of 10 to 15 percent; and carbon to nitrogen ratio (C:N) 25:1 to 30:1. When these components are unbalanced, it can hinder the whole composting process. However, when a compost pile doesn’t break down correctly, it’s not always immediately apparent which factor is lacking or in over-abundance. Below are some common compost problems, their symptoms, and how to remedy them.

Rotten egg smell
If your compost is giving off a sulfurous or rotten egg smell, it might be an indicator that the pile is oxygen-deficient. Composting is an aerobic process, meaning it requires adequate oxygen for decomposition. The lack of oxygen might be from excessive moisture or compaction due to small particle size. 

To test for excessive moisture, pick up a handful of compost and squeeze it. If water drips from your hand, the compost is too wet. If wetness is the problem, turn and mix the pile to aid drying and consider covering it with a tarp or roof.

If particle size appears to be the problem, turn and mix the pile. This “fluffing” of the pile will help create air pockets and reduce compaction. If the problem persists, add bulky particles, such as wood chips, that are about two inches in diameter.

Ammonia smell
A quick whiff of strong ammonia smell is quite distinct. And if it’s coming from your compost pile, it’s likely due to excess nitrogen. Keeping carbon and nitrogen balanced is a necessary tightrope to walk; and if the compost C:N drops below 20:1, the pile may become rancid and sludge-like. Nitrogen is also lost to the atmosphere at high rates as ammonia (hence the smell). To increase the C:N, carbon sources such as straw, corn stalks, or wood chips can be added to the pile.

Pile doesn’t heat up
One of the most common problems in compost is that the pile does not reach high enough temperatures for good decomposition. There are a variety of reasons this might be happening.

The pile might be too small. A very small pile will not have the mass to maintain high internal heat. This one is a simple fix: just make the pile bigger. The absolute minimum size for manure composting is three feet by three feet by three feet. Another common reason a pile isn’t heating properly is that it is too dry. If you do the squeeze test (as described above) and the compost does not hold its form and crumbles apart, it is too dry. To fix this, simply add water with a hose or bucket while turning and mixing.

Lack of nitrogen might also be the problem. To remedy this, add nitrogen sources such as grass clippings, soybean straw, or hay. Lack of oxygen can also cause heating problems. The same rectifying methods of increasing oxygen through turning and adding larger particles apply here, as they do above for “rotten egg smell.”

The pile might also resist heating if the weather is cold. During the winter or a cold snap, turn and mix the pile less frequently. Also make sure the pile is large enough to retain heat; at least five feet by five feet by five feet. Or, finally, perhaps the composting process is complete. If the pile resembles soil, has an earthy (not manure) smell, and is crumbly, the compost is probably done and does not need to heat up any more.

Overall, knowing what might be causing a heating issue or foul smell can put you on the right track to identifying and fixing the root problem. Of course, each problem may not exist alone, and the compost can have multiple problems simultaneously. In those cases, you’ve got to put on your detective hat and analyze the combination of symptoms to find the problems and their solutions. •


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