I did not know this. Thx for posting it.

Lloyd

I've seen horse manure composts that contain as much as 43 lbs. of lime per cu. yd. I am not a fan of that stuff at all for around here. Although for acid soils.....two birds with one stone. (and a free stone to boot)

Gee..........this old dog just learned something of value. Thanks. I am here in the Northeast in moderately acid soil. We have no reason to fear reasonable use of horse manure because we usually need more lime too.

I would compost that pile of horse manure. When it is finished compost it will be at PH 7 or very close to it.
Then you will have a usable product. You of course would need to add lots of browns which could be at a ratio of 1 green to 6 - 10 browns. Time will solve your problem if you have the time and space to work with it.

When it is finished compost it will be at PH 7 or very close to it.
That's a pretty good rule of thumb and works well in regards to most composts when you're just dealing with decomposing organic matter.
However, the lime makes for a special case. The organic material can break down completely but the lime is still reacting. The compost I was talking about in my last post was well decomposed and determined "mature" via Solvita testing but still had a pH of 9.5.

We've seen other members post some things to consider before using HM. De-wormers, pest control chemicals used in the stable, other meds given to the horses being among them.

What I am taking from all these is that one should ask the supplier what else is in the manure. I suppose that would apply to any manures one gets where one does not know the animals or owner.

Again, thx for bringing this up.

Lloyd

How would composting the manure (even if it was fresh) neutralize the lime? I don't think that is possible; lime is a mineral, it's PH should not be altered at all. I figure if pure limestone is alkaline and lime (kiln-dried limestone) is as well and portland cement (kiln-dried to the point of molecular breakdown) is as well, then nothing can alter the PH of limestone other than an acid.

You can add sulphur to it (gypsum is limestone that has been chemically changed by sulfuric acid), or maybe even vinegar. When invading Ancient Rome Hannibal (I think it was Hannibal's army) climbed up a mountain and down an inaccessible pass by pouring sour wine (aka: vinegar) on the limestone and heating it until it broke apart in order to carve a walkable pass through the mountain.

Normally I'd just add a lot of pine needles, but I have naturally acidic soil, so that'd be enough. In your case, with a PH of 10, and pine needles slowly neutralizing, it probably would not be enough. I'd chemically alter the PH with an acid. If you have a truckload of free manure I'd think a few bottles of cheap vinegar would be worth a try; they sell white vinegar in gallon bottles for a couple dollars.

The high PH is probably not an issue for many people, if their soil is acidic, but for those of us with alkaline soils, it's worth thinking about.

Another thing to consider (if you're in an arid climate) is that manures are often high in salt. That's not a problem in areas that get enough rainfall, but it's a consideration for those of us in arid climates.

Lime is added to manures to aid in odor and fly control where there is too little organic matter in the manure to do that. I can remember a discussion with my farmer uncle many years ago, after this was posted, about why that was done and his comment that only those that do not properly manage their manures would do that.

Wow, that's not ground limestone either, which would be pH 8.3. That's ag lime, the powerful stuff.

Lime also reduces the offgassing of ammonia from the urine, by keeping it in the soluble ammonium hydroxide form, if I'm not mistaken.

Re: neutralizing during composting, I would think that the weak organic acids produced during composting would react with the lime and neutralize at least some of it. I wouldn't depend on it getting to neutral from that alone, but I would be surprised if it was still where it started after composting was complete.

After thinking about this I may have mis-spoken about the effects of lime on the urine nitrogen. If ammonia is present, it is normally in equilibrium with ammonium hydroxide:

NH3 + H2O NH4+ + OH-

The OH- being hydroxide, i.e. alkalinity. If you were to add hydroxide to this system, it pushes the equilibrium to the left, toward ammonia, which can evaporate away. This would not have the desired effect of reducing odors.

Of course, it doesn't start out as nitrogen, it starts as urea or urinary porphyrins or who knows what, so I may be off center here.

Somebody tell me exactly why lime is used on horse manure for odor control, and how it works, because I don't get it.

No major concern for horse manure. Yes there are some stables that use lime for odour and horses do get de-wormers etc but this is minimal. If you get a small farm, maybe someone with a few horses the manure will be stable.

"Somebody tell me exactly why lime is used on horse manure for odor control, and how it works, because I don't get it."

Lime really isn't for the manure or even odor control, it is used to neutralize the ammonia created by the urine in the confined space of a stall. Breathing ammonia--regardless how it smells is hazardous to a horse's respiratory system.

The lime is usually spread on the stall floor during the mucking out process then fresh bedding placed over it. I've heard of it used most often in stalls with dirt floors as there is often a preferred spot for the horses to urinate that becomes saturated and difficult to keep dry. Ammonia is only a problem when the urine soaked bedding and dirt floor become saturated and don't have good air flow.

I agree with the farmer uncle, lime is a stop gap measure to compensate for poor horse management. When stalls have mats on the floor (or other impervious material) with bedding on top of it, and/or the stalls are cleaned on a daily basis there is no need for lime.

From a composter's point of view I would assume composted manure (which would almost always include some sort of bedding material) from a barn that uses stall mats would be preferable anyway. In those cases the bedding material would hold and contain most of the urine as opposed to it being absorbed in the stall floor.

So the reality here is the horse manure is fine...

Its lime in the west which is a problem...

I hate posts that say "The Danger of Horse Manure" when in reality they mean "sometimes people put lime in horse manure" and its really "Know your Horse Manure!"

Well, another thing to be concerned about. I've used lots of horse manure over the years and made sure I avoided manure after deworming meds had been administered. So, after this scare, I emailed my horse manure source this afternoon. She told me she has never used lime in the stables and doesn't know any horse owners who do. What's next?

And then, of course, there is this.

tj

@vermontkingdom might be a western thing, I've been around horse stables and never seen it done before either. Still around central MA I wouldn't mind at all, it'd cut down on the lime I have to spread...

We've got a major garden emergency on our hands. We've been getting horse, cow and chicken manure from neighbors for 35 years and have never had any problem other than weeds which are easy enough to control. But I suspect this lot of manure has had a lot of lime put in it. The pH when we finally tested it was 8! I realize that is a lot better than 10 but still does not make for happy plants. I'm wondering if any of you recognize these symptoms: necrotic edging on brassica leaves, general failure to grow, lower leaves of tomatoes yellowing, squash plants yellow and dying and miniaturization of broccoli plants and heads.

Oddly, the celery looks fine. We've been amending the beds that have the least manure in them with home made compost and scraping off the manure where it is possible. I should mention that this is aged and rotted manure which in addition, sat over the winter with a tarp over it.

Unfortunately we had added quite a bit to our beds and incorporated it into about 1/3 of the garden and luckily have mostly not planted in there. Do any of these symptoms correspond to just a high pH or do you suspect there might be some other chemical that was used to treat the horses that might have affected the composted manure this way? I haven't been able to talk to the manure providers. They seem to be away.

The area of the garden where I used compost rather than the manure are thriving and looking uncommonly healthy and well.

Been gardening a long time and never bumped into this before!

Miriam, did you find out if your neighbor added Lime to the manure?

Also, have they changed their source for hay for the horses or did someone start using a herbicide they haven't before? Is it possibly a herbicide carryover?

pH 8 is not bad, remember it's being incorporated into several inches of soil. Even a 50-50 mix of pH 8 manure with pH 6 soil still gives you a pH of 7.

My neighbor seems to be away. But my husband just told me that when he tested the pH it was bright purple, not murky like the 8 that is registered on the color code. It's just a cheap little kit. I suspect that the manure is closer to 10 and the beds that have a little in it are closer to 8.

ai, yai, yai. No, I don't know if herbicides are at play but as soon as my neighbor is back I guess I'll find out.

I don't have access to horse manure, but I am curious by the statement that when you compost manure that's limed, the PH will go to neutral. How does that work? Does the microbes actually break down the minerals?

Paul

I will take a stab at that. There are weak organic acids floating around in an active biological system that can react with lime to produce salts. It all depends on the relative amounts, and you have to keep in mind that every 1 unit of pH = 10 times more alkali as you go up the scale. So I'd say the composting process will have *some* effect in bringing the pH *towards* neutral, but if it's very high the resulting compost can still be at high pH.

I am pleased to announce that with the help of our soil and plant extension agents we have figured out the problem with horse manure in the garden. The problem was not Ph as I originally thought. It's true the horse owner did use PDZ in moderate amounts and that might have contributed to bringing the Ph up. But the real problem was that the manure he brought was not nearly as aged as I'd thought. Apparently even fairly fresh horse manure doesn't have much odor so I couldn't tell. The pelletized sawdust they use for bedding is the problem. It sequestered the nitrogen in the soil so plants were suffering from nitrogen deficiency. I'm very relived it wasn't a problem with herbicide or some other chemical. As time goes by, plants are recovering. I assume the sawdust is mostly broken down and the nitrogen in the soil is freed up. We also side dressed with Pro Boost that has 1/3 chilean nitrate in it so the plants got a major pick-me-up. Thanks all of you for your help!

Thanks all for this great, educational discussion and article links!

Animal manures are somewhat alkaline and may raise the soils pH some. But if those animal manures are composted with adequate amounts of vegetative waste the bacteria digesting that material will change it and the result will be a soil amendment with a near neutral pH that does remarkable things in soils.

Here is a link that might be useful: About animal manures

I have checked & have not found a stable that use lime in the stable.
Some have said line in stables is a bad sign & you should not keep your horses there.

I learn SO much when reading threads like this. Thanks, everyone!!