Stinky cat pee and how to deal with it

A neighbor of mine is kind enough to feed and spay/neuter a group of feral cats in the 'hood (our neighborhood is near a park that strays are often dumped at). However, after a rain or irrigation, her yard is quite stinky. Anyone have any ideas how to neutralize or counteract the cat pee smell?

We were thinking about aromatic plants. Or maybe charcoal?

Is the yard in question a small enough space that it's basically one huge litterbox? What else is being done with the space? Most cats outdoors bury their pee and dung, unless they are toms which are spraying. But if the soil is compacted or the space is very small or there are too many cats, I imagine there's still be smell. The smell is ammonia....basically valuable fixed nitrogen offgassing to waste. The answer is carbon....organic, fairly fine-particled, moist, preferably half-composted....something like half-rotted sawdust.....which will absorb and deodorize the urine. But ideally it needs to be kept moist, and the microbes active, to do this well.....if it is a dry climate with a long time between rains there may be smell, as you say, when it becomes moist again. I've been experimenting with scrounging/making my own cat litter for quite a while and my conclusions are based on this. Adding some ash helps too. But eventually the mulch needs to be changed out (and all the while I'm scooping out the manure and putting this into my humanure system) and replaced.....

Charcoal (biochar) is your general, all-purpose adsorbent, capable of holding onto lots of compounds and by doing so, keeping them out of the air (and your nose).

If cats are marking, they generally choose a vertical object like a tree trunk or fence post, because it signals better to other cats. You can beat them at this game by taking a cup of urine and randomly marking your territory with your own smell. Fortunately, it doesn't take much, and we humans have such poor noses, that we can't smell it much or at all, but to a cat or a dog, it is a big, flashing neon sign that says "KEEP OUT".

Now if they are using the flat ground as a litter box and that is retaining an ammonia-like smell, then you've got a pH problem. Ammonia is a base, and when an animal pees on an alkaline, desert soil, there is nothing for the ammonia to react with, so it lingers. The usual solutions for lowering pH, like adding organic matter, will solve a lot of this problem.

And for small volumes of material, like a cat box, there are things that you can add to the cat litter so that the ammonia is absorbed. Citric acid will react with ammonia to give ammonium citrate, and potassium alum, which is used in pickle recipes to help the pickles keep their crunch, will also react with ammonia.

Alder and John - excellent suggestions.

--The property is 150 ft x 50 ft or 1/6 acre - a small city lot.
--It is in Phoenix - so definitely DRY.
--The lot is currently "desert landscape" - basically soil, covered by landscape fabric, then pea gravel mulch with desert adapted plants growing in holes cut through the landscape fabric (which has micro-funnels in it).
--I haven't checked closely but I have a feeling the smell is both pee and spray. Although she has spay/neutered the colony, some will still spray. Will anyone's pee work to "mark" the territory (not just males?)
--We are slowly working on removing the pea gravel and landscape fabric, building water harvesting features (infiltration basins on this flat property) and planting a desert food forest - but this will take some time. The ultimate goal is to rehydrate the landscape and mitigate flooding that takes place during rain events at that low end of our 'hood. So there will be much more organic matter coming in over time and the site will have more water retention properties than it does now.
--Fort the time being - would you think that activated charcoal like one finds in aquarium stores would stave off some of the smell? I don't think the cats (5 of them currently) are going anyplace - they are settled and healthy.

Many thanks for your insights - I was stumped on this one.

John - I am wondering about citric acid - would citrus peels scattered around make a difference, I wonder? Citrus season is just starting here.

Activated charcoal at an aquarium store is a waste of money (for this purpose). Ground up citrus peels that you get for free -- now you're talking! If you have a heavy duty blender, whiz them up with some water and sprinkle that over the offending smell and tell us how it works out.

John Elliott wrote:Activated charcoal at an aquarium store is a waste of money (for this purpose). Ground up citrus peels that you get for free -- now you're talking! If you have a heavy duty blender, whiz them up with some water and sprinkle that over the offending smell and tell us how it works out.

Will do! Maybe we will finally find a useful purpose for all the "mock oranges" in the 'hood (other than an over abundance of marmalade making material).

I'll report back when we have news.

I have been told that the problem with cat pee and poo is the ph?? Somehow cat pee was worse for plants than even dog pee. It would be great if I could just compost it, perhaps in a separate compost pile or bucket with worms? Are pathogens a concern if it isn't a hot compost (the less attention needed the better)?

I would also like a discussion about various litters. Natural/Organic litter is expensive, the clumping is easy to keep "clean" and cheaper in the long run, short of my digging up dirt from somewhere on my rocky property here in SW New Mexico. I have 9 barn cats going into this winter (with population fluctuations) that will poop in any soft disturbed dirt they can dig, especially in the floor of the barn which is why I provide litter boxes and they seem to like the 'sand.'

Which brings up another question regarding chickens eating cat poo. There doesn't seem any way to prevent it as the chickens make soft dirt and I can't follow the cats around the chicken yard all day. The girls really seem to relish it, I presume for the partially digested stuffs. I do believe that we are kind of a 'closed [pathogenic] system' here but I do share the eggs with neighbors. Thoughts?

Cat litter is just clay. Absorbent clay. Like what underlies half the state of Georgia. It's a triumph of marketing to convince people they should spend money to buy a bag of dirt for the cat to dump in. Of course a little science and engineering has to go into that marketing to make this dirt special -- so that it won't stink like regular dirt from the back yard. Clumping agents are mostly bentonite, where the swelling of the bentonite when it gets wet causes the clump to form.

There are all sorts of tricks to remove the ammonia smell in addition to the citric acid I've already mentioned. Baking soda is not really effective in absorbing the odor of ammonia, because the product formed, ammonium carbonate or ammonium bicarbonate, easily decomposes to give off ammonia and carbon dioxide. But almost any amphoteric compound can be used if it will bind ammonium ion and give off hydrogen ions. If you have some sauerkraut juice, the lactic acid can bind up the ammonium ion, forming ammonium lactate. Of course, then you may have the problem of the cat not wanting to use a litter box that smells like sauerkraut.

I would imagine that your "closed [pathogenic] system" is already host to Toxoplasma gondii, since it is not that closed and the cats may be eating all sorts of wild rodents. Best thing to do there is to follow the rules for how to minimize exposure, the most important of which is to cook the eggs. The way you can tell if the chickens are having a problem with the toxoplasma level is if they start showing neurological signs. Which, come to think of it, might explain another mystery that I haven't yet solved.

If it was me, I would forget composting cat poo and put it in a biochar burn. That'll take care of those nasty pathogens!