Not sure on how long it takes for fecal matter to break down. There are various factors involve to properly maintain a bio-active vivarium. There is also a need to turn the soil around too, to keep thing 'stirred up'. Worms and other insects in the soil certainly can do alot of this for you.
Best way to get a deeper understanding on how this works for a semi-arid setup is to google arid or semi arid vivariums, or Live Vivarium setups. Reptile Magazine has had a few articles in the past relating to this and of course for rainforest and forest style vivariums, there are much more info out there. Arid, semi arid or dessert type vivariums not as common but still possible.
All this talk about the value of having some humidity for bearded dragons makes me wonder if a low humid hide would benefit them especially in cages that don't use loose substrates. Humid hides are often used with snakes and other humid needing lizards. I think its even recommended to have a humid hide for many gecko species, even those who normally come from a semi-arid environment (ie leopard geckos). Though leopard geckos are nocturnal and don't 'bask' in the heat under the sun, they do hide all day...
The following is addressed more to TheVirus, Kmartin and BDlvr:
There are still many variables and unknowns with bearded dragons and though these boards do invite name calling, please, do remember it is against the TOS for anybody to 'bash' another. Its fine to say 'I don't agree with what you are saying' but be tactful, and leave out the 'no you are wrong' type phrasing. I really do hate having to remove some good posts because either they contain TOS violations along with the good info or enough of a reference to a violating post I have to pull it too.
It is clear there are many different ways of doing things and not all are bad. The important thing is whatever is done, is producing a healthy thriving animal. There are pros and cons with each method but if the pros far outweigh the cons, then its a good setup. Nearly all reptile keepers and breeders started from not knowing anything about the proper care...and over years and peer discussions (even before internet was so readily available) used trial and error to come up with the best way to care for their animals.
My strongest suggestion is always keep an open mind, even if the new information seems radically different. Analyze it objectively and instead of automatically rejecting it cause its different, try and see why it works so well with others. Length of time keeping bearded dragons or reptiles etc. does have some value, numbers of total animals and overall age of dragons is important too. One could keep bearded dragons for 20 years but never kept an adult past 4 years of age isn't quite the same as keeping bearded dragons 20 years and each one they own they kept from egg to grave...with them living on average 10 years.
Pets and breeder animals are a bit different too, as most breeders tend to sell off older animals that are past their breeding prime, replacing them with new blood from different lines or offspring of the 'retired' pair. Or a combination of both. Large scale breeding operations also have space limitations and resort to the simplest and most efficient methods...mostly due to space and cost concerns. This means their methods of husbandry are likely different than the hobbyist who just has a couple dragons as pets, maybe with some breeding on the side. And of course everybody in between.
I have been around these forums and other forums for about ten years, maybe longer, now. I have heard all kinds of different ways to care for bearded dragons. Some don't work at all due to sickly animals etc. Others have used methods against the norm without problems. Even using things for substrates I would never even consider...such as seeds and rabbit food. Each them these odd things come up I logically try and figure out why it would work or not work, what are the pros and cons..so I research. I don't' always keep a lengthy record of where I read things and some sites may be bogus, but I do try and find more than one source of information, to better validate it. I also ask questions, especially during the special guest chats we have.
There is still plenty for me to learn. Alot of times there just isn't any information to find out due to lack of real research. I would love to do some of this research myself, in a controlled environment..but I lack the money and space. Like buying every brand of calcium based sand on the market and finding out if it can actually be digested as the bags all claim. Then I heard of somebody on these forums or the chat rooms, who tried this himself. Found that even using acid stronger than is typically found in animal stomachs, calcium sands don't break down sufficiently even after 24 hours. He drained the acid away and dried the remaining sand, weighed it and it was exactly the same weight (or a tiny fraction of a difference). It also clumped up and reduced acidity of the acid.
I would love to do this test myself, but I have no access to the tools I would need. If I was still in University, I could use the Chem lab for this easily. Things I don't know about that particular test was whether he used an agitator with the acid/calcium mix (an agitator will simulate the movements of the stomach as it churns etc during normal digestion), among other things.
I would also love to have several clutches of dragons...raised them up all the same, then breed them and each baby from these raised from hatching to full adulthood under several different conditions, with weekly and monthly testing to monitor growth, bone density, levels of calcium in the blood etc. to see if they thrive better in different situations. Such as no UVB conditions (heat light, no source of UVB at all. No supplements at all. One with supplemental Vitamin D3, etc. to see which group thrives best..
Oh the things I would do if I had unlimited funds
I have rambled on long enough..I hope this proves interesting to anybody who has taken the time to read my latest long winded post.
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PHLdyPayne