Are there any known Creo Terram guidelines for changing/improving qualities of any particular earth (such as steel to alchemical steel, or average soil into chernozem) instead of just creating the enhanced stuff separately?
I'd think there would be, but I don't see it in the Spell Guidelines pdf.
There are guidelines for transforming Terram under Muto, p154 which may be slightly useful in generating CrTe guidelines.
Yes, and they're in the spell guidelines pdf, too. Take a look at CrTe3 and ReTe3 bases from A&A for reagents. You need to learn how to do it via experimental philosophy first, though. And then there is the Finesse roll...
So no simply improving something through magic like you can improve someone?
Guess I'll just create steel of maxed quality out of thin air, no philosophy required (just +1 magnitude).
The relevant rules for this are foremost on ArM5 p.77 Creo (Cr) "I create" and HoH:S p.60 Creo Magic.
A&A p.70 box Replicating Formulae with Hermetic Magic addresses creating A&A p.76 Alchemical Steel.
See also Mass-Produced Reagents for another discussion on a similar topic.
Cheers
The fundamental assumption used is that the understanding of how to go past good steel as used in weapons is not available unless researched, so I would never let that fly as a Storyguide. It's essentially the same thing as saying you'll skip picking up a Mystery, instead just adding a magnitude to something for complexity to allow you to do what the Mystery Virtue allows.
Some smiths make better steel than others, such as the famous Damascus steel. Which one is the limit for Hermetic Magic? A magus without smithcraft wouldn't understand how to make even "normal" weapons-grade steel, so it's not easy to reduce to a matter of knowledge.
Maybe not just one magnitude for complex items, but I would prefer a system with a simple and consistent system. Hard creations should be very high level spells, not low level spells requiring a strange and complex subsystem from a book many players won't even have. It's natural that AM5 has become so baroque over it's long life but that's not a good thing in cases like this.
You can use ReTe to improve soil quality. And you do not need vis to make it permanent nor have crops become warped. Richer, more fertile soil is just another state of soil.
This is already handled perfectly well with craft magic, either Rego or Creo. There is a difference between crafting well and making what is ultimately a different material, at least in ArM5 terms.
And it's perfectly fine for Storyguides to choose what to keep and what to drop. If we're not worried about what is in the canon, that's fine. I was basing my replies on the original query about existing guidelines in the rules as opposed to how one might go about replacing those guidelines.
Yes, as similarly you can use ReTe to work iron into different types of iron/steel, as is done in Covenants.
Actually, I'd argue that it's the best thing in cases like this. For one thing, old magi are really powerful, and Ars Magica characters don't tend to breach the upper limits of what characters in the setting can accomplish unless many things are heavily altered in that saga to make the unusual power growth possible. So any effect that might radically change the setting but hasn't needs the justification of "why," and a fairly elegant answer to that is "because no amount of pure power or vanilla knowledge will let somebody figure that kind of magic out." And keeping that out of the core rules both helps prevent clutter and makes it easier for new players to keep in mind what the general Order has access to.
Plus, while I admit this is just my own perspective, I think Mystery Cults and other things demanding not purely Hermetic experience (which I'm just going to refer to collectively as Mystery Stuff) only add a little complexity (as in they only demand a little bit of effort to understand) while adding a lot more depth. Mystery Stuffs allow for a meaningful opportunity cost in power that have a hard time coming into existence with how overwhelmingly powerful Hermetic magic is. Learning a Mystery Stuff generally represents a (small?) step down in lifetime power for the magus, because they take a lot of time away that could've been spent improving upon normal magic, but gives them access to cool and useful abilities that almost nobody outside their Cult (group of Stuff-Users?) has ever had. Adding those abilities to vanilla Hermetic magic just makes them more generic, and removes a path to differentiation and stories.
In my opinion, magi generally don't need to know how the sausage is made mundanely to make it with Creo Animal (and geez I'm mixing my metaphors here).
Magi should definitely not have to do something through a magical imitation of mundane alchemy if there should be a method to do it through Creo alone (as in, "making something a better example of its kind"). There may be a Finesse requirement involved for the steel (not the soil, as soil is a natural thing), but requiring experimental philosophy sounds like something that only makes sense for fatigue-cleansing theriacs (since Hermetic magic can't fix fatigue and theriacs can, at least short-term fatigue).
Not exactly. Fertile soil has MORE of something in it (loam), adding something to it that's not there is Creo.
You can use Rego to improve soil. ReHe to gather vegetation and turn it into mulch/compost (or ReAn to compost manure) and then ReTe to mix the products into the local soils. Composting might be Perdo, but composting is something that's done in a deliberate fashion (it's a mechanical process that's assisted by natural decay), so Rego is probably appropriate.
But no, you can't just cast a single ReTe spell to turn sterile soil into fertile soil. Sterile soil is missing something that must be added.
I wasn't thinking of the craftsmanship involved in forging the sword. There are different grades of steel involved and "Alchemical Steel" sounds to me look a good stand-in for the most famous of them, "Wootz Steel".
en.wikipedia.org/wiki/Wootz_steel
It's a natural substance. If Creo can make diamonds (which it can) I don't see any reason why a high level Creo shouldn't make high grade steel. The A&A rules may offer an alternative path but I don't think that should be exclusive.
Wootz steel indeed appears to be a very good example of A&A p.76 Alchemical Steel to me.
By the wiki entry you quote, it is a crucible steel (see en.wikipedia.org/wiki/Crucible_ ... ly_history ): cast steel made by melting the ore, e. g. black magnetite, in the presence of carbon and other substances in a crucible.
See en.wikipedia.org/wiki/Wootz_ste ... cteristics for research on the process, and a hint on some ingredients passed on only by word of mouth.
Wootz steel is not a natural substance, and making good one requires both good raw materials and a well conceived and controlled carburization process.
The true Ulfberht swords (en.wikipedia.org/wiki/Ulfberht_swords ) were made from crucible steel, so a really interested magus might learn the prerequisites and technical details for making one.
Cheers
For the soil, I would suggest an Mu(Cr)Te spell.
MuTe for the guideline "Level 2: Change dirt to another type of natural earth (for example, sand to loam)."
The Creo requisite to allow it to be permanent with a Momentary Duration Ritual. (+1 for the Requisite).
Range: Touch(+1), Duration: Momentary, Target: Boundary (+4)
Add +2 Magnitudes for Size.
Dirt to Dirt is +0 Magnitudes (Optional: +1 Magnitude for (up to) Stone to Dirt - to allow for any near surface stones/rocks to be converted into chernozem, as well - avoid including stone buildings in the Boundary though. 
)
So you'd end up with a level 30 (35 for the stone version) Ritual that could affect a maximum of approximately five and a half virgates of land if my math is correct.
I don't follow the rationale to Ars magic system of a Muto effect being made permanent by using a Creo requisite. Is there a spell which has done a similar thing?
I understand you're changing the soil which is present. And that creo makes things better permanently with rituals, but not both combined in a ritual.
Couldn't it just be made as a creo ritual, like adding strength?
Or use rego to manufacture better soil and avoid the vis cost and add a very easy finesse check (very easy to make compost).
You can use Rego to manufacture better soil, but that's a mess of requisites like Corpus, Herbam and Animal, plus potentially time and effort - see Gwidion in MoH, page 43 - No Animal requisite there , but if his needed to work on animal dung, it would need one.
There is at least one Cr/Mu (Fo) Momentary Ritual - sort of. Harmonic Metamorphosis of the Beast, page 83 MoH, in the box. It's (really?) iffy, but it's there. I'll do some more looking later and see if I can find something better.
Edit - Harmonic Metamorphosis of the Beast does, in fact, use Creo to make a Muto effect permanent - "The spell compensates for the vast difference in size between the two heads."; Changes in Size are clearly a Muto effect and it's still a Momentary Ritual with lasting effect in the Creo Ritual fashion. There's still the whole un-discovered Breakthrough issue with my cited example, but I'd argue the Breakthrough aspects deal with the Frankenstein stuff and not the Muto/Creo synergy.
It's every bit as natural as any other form of steel or, for that matter, baked bread. Are you suggesting that AM5 Creo can't create these?
Bread is explicitly called out as example of an artificial, not a natural item on ArM5 p.77 Creo (Cr) "I Create".
Creo can create artificial things also. But a Finesse roll is in order. Check this on ArM5 p.77 Creo (Cr) "I Create" and on HoH:S p.60 Creo Magic, and find the difficulty of this Finesse roll described on Covenants p.49 box Rego Craft Magic and HoH:S p61 box Ease Factors for Creating and Crafting Objects.
To create artificial things, a magus needs also to be familiar with them (ArM5 p.77). We can assume this for bread, unless the magus never left a medieval version of Buñuel's Las Hurdes (en.wikipedia.org/wiki/Land_Without_Bread ).
We learn from A&A p.70 box Replicating Formulae with Hermetic Magic, that a magus needs to know the specific formula of A&A experimental philosophy to be familiar with A&A p.76 Alchemical Steel.
In general: the more rare and potentially world altering the item to be created might be, the more arcane and specific is the knowledge required to be sufficiently familiar with it.
Cheers