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Composting Large Quantities of Horse Manure


March 16, 2018

I'm so glad I found this resource! I'm the program director for a horseback riding program in Santa Fe. Our zip code is 87507. We are located on the  Southwest Side of Santa Fe - basically we have dessert, sand, wind, and juniper.

I would like to start a program to compost our horse manure into usable compost. I'm thinking of a three "box" system, but I would like to just build cinder block partitions instead of building actual boxes. Obviously, it would be helpful to just push the wheel barrow in and dump it every time we clean stalls instead of trying to get it in a box. 

I have a few questions. First, is there any reason we would need to compost on a concrete pad? If not, is it enough to compost on the ground, or should be build some other type of floor? 

How often would we need to turn our compost. We could tractor turn it, but turning compost every 3 days is quite the time commitment for our program. Would we need to water our compost before turning?

I haven't worked with compost on this level before, so I would greatly appreciate any advice you have or resources you can point me to!

Thank you so much for your time! I look forward to hearing back!


Answer by JH: This is a great idea and you are asking all the right questions before getting started.

I also have a couple questions. How much manure will you be adding each week and will you add it daily or at some other interval? This will help determine size of and number of bins required.

Also, will you be mixing the manure with other materials, i.e., fall leaves or other browns such as straw?

To try and answer your questions, this type of system you picture is ideal and it does not need to have a concrete floor. In fact it is better to construct the walls directly on the ground. It is also not necessary to turn the piles but you will want to cover them (and weigh the cover to prevent it blowing away) to keep the manure from drying out. The pile does need to start off with and maintain sufficient moisture - about 50%.

You also will need to add some type of bulking material (pine cones, twigs, spent plant stalks and such) to keep good air flow in the pile as it decomposes and settles. Insufficient air flow will cause the pile to go anaerobic which will make for a nasty odor. With that said however, this problem is easily remedied by turning the pile and adding bulking material to improve the airflow.

Again, the pile does not need to be turned. The purpose of turning compost is to encourage a good mix of ingredients to enhance their breakdown. It is also necessary if you are hot composting. This process requires you to turn the cold outer edges of the pile into the center, add greens (aka nitrogen aka manure), moisten and cover. The hot process enables the pile to reach a temp of 150 or more for a period of days. When it cools down below 130 (or approx every 2-3 weeks), the pile can be turned to heat it up again and the process continues until the compost is finished.

This takes roughly 3 months or longer with a larger pile. The minimum size required to hot compost is a cubic yard. I suspect your piles will be much larger than that.

If you do not want to turn the piles, it is not necessary but this method is referred to as cold composting because you will not be generating much heat over a sustained period of time.

It might take 12-18 months or longer to achieve finished compost via this method but clearly it is the less labor intensive approach. And if you are continually adding fresh manure to a pile, this will also slow down the process.

If you are only using manure, I am guessing you want to be careful about how large your piles are. A massive pile of such a rich nitrogen source might catch fire from the center.

We have an excellent compost calculator in the resources section of our website. This would be helpful to you if you are wondering what quantities you need if you are mixing the manure with other items.

Additionally I encourage you to locate a compost class to attend. Our class schedule is also available on our website.

Answer by JZ: Other of my colleagues may also reply to your questions.  Excellent project !

  • Ideally manures should be composted using the hot process.  See our brochure for specific guidelines- intensive/hot.

Ideally the bottom of any composting setup should drain excess water onto the soil, not on concrete.

There is no need to build an understructure.  The first addition to an empty bin is 12” of coarse bulking material spread over the whole bottom surface. Finger size sticks, twigs, pine cones, corn cobs worm well. Then continue to add bulking as you build the pile. This decreases compaction of wet organics and provides for convective air flow throughout the pile.

  • The cinder block setup is just fine with the front access open for your wheel barrow or tractor -  just the way it is pictured.

  • You would decrease evaporation moisture from the pile by covering the whole thing with a tarp, when you are finished working with it. Then put rocks around the edge of tarp to keep it in place.  Covering the pile will also decrease flies and other flying insects.

  • Hot process guidelines are in the brochure.  Your pile temp should reach 130 -150 F in about 3 days, then allow it to process for 7-14 days at that temperature. Then turn and churn it, repeating the same process until humus is formed.  Sure you could use a front end loader to turn the pile. It is not necessary to turn every 3 days.

  • Yes, sprinkle the pile before turning it to keep down the spores that may rise up.  Maintain 50-60% moisture throughout the process.

You would be welcome to attend any of our free classes anytime.

Let us know if this helps / if you have more questions.    All the best.   You are doing a fine thing.  Keep up.

Additional Answer by JZ: Forgot to mention residual persistent herbicides which may be in the feed which the horses ate and will persist through their digestion and persist through the composting process.  So you have to go all the way back to the farmer who grew the horses’ food and find if broadleaf herbicides were used on the field.  This is a long discussion.  I would refer you to the link on our website.

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