Let me get one thing out of the way, first off, to help people grasp the important part of this concept:
[size=12]Fertilizers must be expensive[/size]
I don't mean "expensive to buy from a caravan", I mean that they are rare, precious, and difficult to obtain, and worth conserving because of the difficulty of obtaining them.
Think Dune for a moment. In Dune, water was so scarce and precious that you not only had to wear a special suit to preserve as much water as possible, but when someone died, a special burial practice was performed to preserve all the water they could, and when nobles threw water out on the floor, peasants would soak it up with rags to keep as much of the wasted precious resource for themselves as they possibly could.
Fertilizers, likewise, need to be something that is really, really easy to waste, but for someone who needs every edge they can get, worth going through every possible trick to reclaim as much of that resource as they possibly can.
This means poo, by the way. I'm talking about getting poo up to being a resource people cannot afford to waste by merely throwing it out and ignoring it. And yes, this
is a serious subject.
If we are going to make this a game where advanced farming is based around farming in crop rotations, and the "gaps" between the fertility of the field after one crop is done with the field, and the place where the field needs to be for the next crop to be able to grow are bridged by adding fertilizers (what I am proposing), then the key game balance issue upon which this entire system becomes either a brilliantly crafted challenge for new and advanced players alike, or a miserable joke where every problem can be solved by simply slapping the button for adding more of your nearly-infinite resources to the problem comes down to one major question:
How precious is your poo?
Yes, I'm serious, quit asking!Making fertilizers that come from biological waste your primary source of fertilizer serves the important balancing purpose of giving you a set ready amount of fertilizers that you can use based upon the number of dwarves and livestock that you are actually feeding with your plants.
Here's another important aspect to remember with using fertilizers, however: They rarely have one direct effect for using them. There are about a dozen different variables for soil for a
reason. Everything you do to the soil will have an impact on more than one variable, not all of which are good. This means overreliance upon any single resource will come back to bite you later on when you've managed to turn your soil toxic by trying to just apply the same fertilizers in absurd quantities to just force your soil to keep growing a single crop over and over. To that end, I'm adding in some little guideline + and - symbols next to some of the fertilizers so you can keep track of what sorts of things this might have an impact on.
Urea - Untreated
urine contains mostly water and a chemical called
Urea. As a nitrate, it is useful both as a source of Nitrogen in the soil, and as an ingredient for the concoction of explosives, including Saltpetre, one of the key components of gunpowder. Urea is broken down by common bacteria that live in most soils into ammonia, which most plants use as their nitrogen source. Spreading untreated urine on your fields replinishes the most nitrogen for your buck (as well as phosphates and potassium to boot), but can have unintended consequences as it may raise the total soil bacteria population up to dangerous levels, and kill sensitive plants with biological toxins, add to soil salinity, is typically acid, and generally "burn" plants (biological toxins). Some plants may be resistant to this burning, however, so weed-type plants are perfectly fine with you just going to town on them. It is possible to dilute urine in water significantly enough that untreated urine can simply be applied directly to the fields. A special function on the irrigation pumps may make this a decent idea.
Lant/Ammonia - Functionally, urine that has been allowed to age and to have bacteria process and break down the urine outside of the soil itself. This is the primary source of ammonia in the Middle Ages and Ancient times, and was used quite extensively as a cleaning agent until the invention of the Haber-Bosch process in the 20th century. (Yes, treated urine is used as a cleaning agent.) Ammonia is generally known to be a weak base, as opposed to urine, which is generally a weak acid. Both these would be impure forms of urea and ammonia, but the general rule should apply.
This means we will need to have some sort of "Gong Farmer" job, and chamberpots, although "sewers" are pretty popular with the crowd that wants biological waste in the game. If we use sewers, collecting all the useful urine, and separating it out from the common water and solid waste may be more difficult, and may require dwarves whose most unfortunate job it is to actually strain out the useful urine from the useless other waste that goes in the sewers.
In some communities where Lant was positively necessary for the industry of the area, however, it should be noted that there were communal requirements that you actually save your urine, and keep it separate from any other waste so that as much of it could be harvested as possible. How, exactly, such an edict could be put in place over your subjects, and what its social ramifications are might require further discussion, however.
Manure and
Night Soil - Solid waste provides another form of fertilizer, although, as the stuff the body couldn't use, is not quite as useful as a direct injection of nitrogen as urea is, although it would work well as a means of building up the humus layer. Night soil is the manure of humans (or in our case, humanoids), and can put potential parasites and pathogens into the soil above and beyond the problems of regular manure. Human waste also carries heavy metals, which can gradually accrue heavy metal pollution in the soil. Applying manure or night soil directly to the fields can "burn" plants, which cannot take the increased bacterial activity and biological toxicity. Composting the manure or night soil, however, leads to a significant drop (up to half) in the nitrogen content of the night soil, while at the same time, mitigating many of the downsides. May also add pests in the form of parasites and diseases the host animal passed out.
Compost - Night soil and manure left to compost outside the fields allows many of the biological processes that decompose those materials to take place away from the plants, where the toxic chemical byproducts of the funguses and worms and bacteria do not harm the more delicate of the crops you grow. Composting can be done by a vat filled with fecal matter with worms to go at it and the like, but we might also try "composting by farm", and grow some kind of mold by tossing waste on it. This would mean growing a type of "crop" purely on manure whose sole function is to generate a "fruit" of fertile soil for collection. Composting can also take place with dead organic matter of all sorts, including clothing, wood, rotting food, dead creatures, etc.
--- I cut out the non-waste-related forms of fertilizer, but the post goes on to cover decomposing dead creatures and mineable fertilizers ---
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