Spreading vs. Composting Manure

A couple months ago, I decided I was fed up with shoveling stall waste into my compost bins only to shovel it back out again a short time later, and I decided to try spreading manure on the fields directly (post here). I think it is about time to update with the results of this experiment.

As expected, spreading the stall waste directly on the fields was a nice timesaver. Rather than dreading shoveling out the manure bin once a month or so in the summer, every week I hooked up the tractor, toodled on out to the field, and spent less than 10 minutes driving around emptying it. Bing bang boom, no shoveling involved. I monitored temperatures in the spreader as I would in the compost pile and found that even without any aeration, the waste would naturally heat to over 140 degrees, hot enough to kill weed seeds and pathogens.

My two horses were on stall rest at the time so they were filling the spreader up in about a week, and probably would have filled a compost bin in 3-4 weeks. As the horses started to get turnout again, I spread the waste on sections of the paddock that they weren't using.

The one downside is that I have to remove the tractor's PTO arms to use the spreader, which was kind of annoying when done on a weekly basis (though not nearly as labor-intensive as cleaning out the bin).

You may notice I'm writing in the past tense...this is because I stopped this method after about a month out of concern for how it was affecting my grass. Here are some photos:

This photo was taken just days after spreading some fresh stall waste and you can see how it already burned a swath of grass.

Close-up taken the same day as above.

Two weeks later, the very lush late-spring grass appears fully recovered.

As you can see, the grass suffered what I believe to be nitrogen burn from the direct spreading, which has never happened when I spread even briefly composted manure. At first I thought this might be caused by the added ammonium sulfate, so I cut down on how much I was adding and then stopped adding it entirely. The burn continued. The grass did recover within a couple of weeks, but I was concerned that it wouldn't once summer heat and dryness set in, so I stopped direct spreading and switched back to compost, despite its flaws.

I think the direct spreading method could be perfectly fine if you have more acreage and don't need it all for grazing, but since I have to spread on my meager three acres of pasture I really don't want to damage any of the grass.

So I was back to composting, and still wondering why it didn't seem to work very well for me. Fortunately my local Soil Conservation District has some great staff who can troubleshoot issues like this. One of their helpful staff members came out in June and after examining my compost pile (which involved standing in the full bin and digging a deep hole), he said: 

A couple fingers are pointing to the possibility of a moisture imbalance in your compost, which may be brought on by you selectively removing only urine-soaked shavings from the stalls. At least one of the people I talked to mentioned how without drier materials to reabsorb it moisture can migrate from the top of the pile to the bottom, causing anaerobic conditions in the bottom while limiting the ability of the waste material on the top to be composted. This may go far in explaining a bottom layer which was warm mud that smelled like ammonia, a middle which was hot and actively composting, and a top which was warm but not doing too much. This is not a dynamic that could be seen in a wheelbarrow from a barn or one that can be addressed by a forced air system. It is simply physics. Adding more dry shavings might help with it, but it may also skew your C-N balance.

So apparently I clean my stalls too efficiently by removing only the manure and soiled bedding? The thought of deliberately throwing away clean shavings just to make my compost pile happier is anathema to my frugal, anti-waste nature, so I am looking to switch from aerated compost to a traditional multi-bin system that can be turned with the tractor. Thankfully the county also assists with funding for projects like these. Meanwhile, I continue composting and until I have a better system I may just leave the gross "mud" in the bottom the next time I empty a bin, since the top seems to compost fairly well.

Looking down into the compost pile, you can see that it is much darker, denser, and wetter at the bottom. This pile accumulated from last fall to about April of this year (since the horses lived outside all winter, there wasn't much stall waste to deal with).