(LONG post. Probably ninja... Yep, Ninja'd)
Ok, so basically, the idea I had was this:
Water availability:
A tile that is unable to retain moisture (desert biome, without irrigation) will lose biomass per growing season (NOT YEAR!) at a rate consistent with its lack of moisture, with an upper bound of 25% per season. Thus, if not irrigated, dumping compost on it will result in all the compost vanishing without a trace in 1 year. Distance from a water source determines how moist it is, in desert biomes. Exact rate of falloff needs to be determined carefully to avoid game breaking consequences.
Tiles that are too wet (Swamp!) will have a similar problem, even though this isnt exactly RL accurate. (Instead, swamps accumulate biomass, but prevent crop growth, due to toxicity, and lack of aeration for soil microbes, leading to plants literally rotting in the ground, and becoming peat.) Instead, dryness will be dependent upon proximity to dried tiles. (May require a magma source below to force-dry the tiles, or extensive tilling to keep the tiles aerated.)
Rainfall on a tile adds moisture, and on all tiles except swamp biome ones, tiles naturally revert to being parched. Parched tiles lose biomass like on desert tiles.
Weather:
Weather affects the amount of sunlight, and the amount of rainfall a region has. In addition, "Abnormal" weather, like deadly dust, and deadly rain, block out 100% of sun when they are in effect, and in the case of deadly rain, do NOT moisturize soil.
Region:
The latitude of the embark region will determine the amount of sunlight per growing season, and variance between seasons. An equitorial region embark will receive maximum sunlight per season, on all seasons, year round. A temperate zone embark will receive maximum sunlight only in summer, 50% sunlight in spring and autumn, and 25% sunlight in the winter. A polar region embark will receive 25% sunlight in summer, and 0% sunlight in winter.
In addition to geographical factors, effects like "Goodness" and "Evilness" will impact the natural homeostasis of the soil, making it trend more toward fertile, in the case of good biomes, or dead, in the case of evil ones. The degree of this impact needs to be carefully implemented, and needs to be (very) subtle. Little things like this can be used to keep sunberries ONLY in good biomes, and sliver barb ONLY in evil ones, for instance.
The amount of rockiness of the area should also play an important factor, just by being there, since there is no way to remove rocks from a field efficiently without simply flooding the surface, and using mud.
Biomass casino roulette, and plant growth:
Plant requirements are static. A strawberry always requires the exact same amount of energy to grow. As such, there cant be any cheating by starting a strawberry on a tile that doesnt have enough biomass in it to theoretically supply 100% of its needs, should the sun fail to shine for some reason. (Like, it being the winter at the north pole, maybe?)
This means that a tile with 0 biomass will NEVER support life, unless it is fertilized first, and then only support what could theoretically be 100% supplied by that biomass, even if the sun is shining brightly overhead.
Composting is VERY inefficient! It is this way BY DESIGN. At LEAST 50% of the biomass of the source material will be lost, and up to 99% at the top end, based on the crop. here is a tentative list of made up values that look good without being tested:
Sliver barb (Loses 99%)
ratweed (loses 90%)
hideroot (loses 80%)
bladeweed (loses 80%)
ropereed (loses 70%)
Fisher berry (loses 60%)
Prickle berry (loses 60%)
Strawberry (loses 60%)
Sunberry (Loses 50%)
Whipvine (Loses 50%)
Going the other way, different crops produce less biomass than others, as they gain in potency for composting.
Whipvine (yeild: 5 per tile end of season)
Sunberry (yeild: 3 per tile end of season)
Strawberry (yeild: 5 per tile end of season)
Prickleberry (Yeild: 8 per tile, end of season)
Fisher berry (Yeild: 8 per tile, end of season)
Ropereed (Yield: 12 per season)
Bladeweed (15 per season)
Hideroot (20 per season)
Ratweed (20 per season)
Sliverbarb (30 per season)
note how the edible crops are lower yeild: This is intentional.
In addition to this, the consumption rate to produce alcohol closely parallels the costs for composting coupled to yeild and crop size.
1 barrel curor == 500 sliver barb (barbs are low nutrition, AND small.)
1 barrel sewer brew == 30 rat weed
1 barrel river spirits == 20 ropereed
prickleberry and fisher wine == 100 berries (Small)
strawberry wine == 120 berries (small)
sunshine == 120 berries (small)
whip wine == 50 whips
naturally, you should be seeing how it is going to be very difficult to survive now, without MASSIVE agricultural allotments. This is more realistic than most players are used to. Welcome to hell children.
Each soil tile has a fertility ranging from 5000, to 0. Depending on the biome, regional effects, and moisture balance, this will either naturally hold steady, or fall like a gold brick through the atmosphere of jupiter.
Let's play a sample.
Evil biome, North pole. (the infamous "Haunted Glacier" embark!)
Natural vegetation: NONE
Tree cover: NONE
Temperature: FREEZING
Surroundings: TERRIFYING
Site prospect says:
NO SOIL
AQUIFER
DEEP METALS
DEEP STONE
Neighbors: Goblins, Tower, Dwarves, Humans
embark window asks if you REAAAAAAALY want to embark there.
We say yes...
We arrive, and first thing, we dig down into the ice, and hit the aquifer. We have to breach it, so we double slit. We hit stone. In order to get surface crops started, we have to wait several years, and we also have to get magma just below the surface to keep our irrigation system from freezing solid. This means we have to get to the magma sea.
We murder our migrants, and compost the bodies, because we can't make any alcohol yet, and have VERY limited reserves. We make boatloads of stone crafts to sell.
The dwarven caravan for the first year arrives. We sell our crafts, and buy food and booze. Gods, do we buy food and booze. We continue our digging, and then the yetis arrive. Thankfully, we have built a drawbridge with stone mechanisms, and deep stone we got through breaching the aquifer. Then the deadly weather arrives, killing the yetis. We think this is a blessing, but no! NO! the yetis rise from the dead as HUSKS. We cleverly devise a freezing cannon with pumped water from the aquifer to murder them, so they stay dead. The necromancer arrives shortly afterwards. We succeed in destroying his undead army with the water cannon, but he escapes off the map.
The humans show up. We sell them more of our useless stone goods, and buy wood, and surface crop seeds. With the leftovers, we buy more food and booze. With the wood, we make SORELY needed beds, averting that tantrum spiral that is imminent from always drinking the same booze, sleeping on cold stone floors, and seeing the undead, and witnessing death (Murdered migrants, remember?).
We have now reached the magma sea, and constructed a minecart dipping system to transport it to the surface... but need wood for powered rollers. Our embark doesn't have a cavern layer.
Dwarves arrive, and we buy the wood we need. We buy more food, and more booze. Shortly after they arrive, the goblins spring from ambush, killing some of the dwarven merchants. We compost the bodies. (both dwarven and goblin) Shortly after, we channel the surface, and start dumping magma in. Combo attack of evil weather, Tower attack, and Kobolds. It isnt pretty. (thank the gods we used a bridge!) By the end of it, we have several new ice sculptures, a magma cart that has been derailed, job cancellations of doom, and monsters that refuse to get in range of the ice cannon.
Summer rolls around, and the humans show up. More deaths-- but they break the seige for us. We compost the bodies, re-rail the magma cart, and put a stone block floor over the magma pool, along with a privacy wall around the crop yard. We FINALLY pour water on the constructed floor over the magma pool. MUD! HOORAY!.. but wait.... it has ZERO fert! OH NOES! Well, we have about 10 units of compost from all those bodies... so, we put it on. Ok, our 1x5 plot now has a whopping 2 fert! (10/5=2) whee......... Ok, we can grow... NOTHING. Great. (Humans dont have sliver barb seeds. Ratweed needs at least 10 fert. We should have made a 1x1 plot, fertilized to 10, and planted ratweeds... but we didnt.)
The season comes and goes and... whats that? the fert dropped to 1?! ARHG!
Now we get serious. We ask the trade liason for turkeys, because CLEARLY we arent gonna be growing any damned plants any time soon, and it is ALREADY year 3, and by then, the plot has returned to being 0 fert.
The turkeys arrive next year, after we buy out food and drink from the human caravan again. Stone is getting a little more scarce now, so we build an obsidian machine. We have been dutifully murdering our migrants by blocking them outside until they die of thirst and starvation, and then composting thier little fat dwarven bodies this whole time. We are now officially a death trap. We put out nest boxes, and hope for the best.
Another year.. Another round of sieges.. More migrants we euthanize.... our dwarves have DARED to get married and start producing babies. (HOW DARE THEY!?) We now have a steady supply of turkey poults being pooped out! We butcher their asses, and compost some of the turkey skins. We thankfully have had only metal and stone moods so far, and none have needed any bones or other cloth... Cloth.... our clothing is looking rather tattered. We will probably have to order some.
Year two after ordering turkeys. We are now swimming in adult turkeys. We enable egg collection, and start composting the SHIT out of turkey eggs... watch painfully as it requires absurd numbers of them to produce 1 unit of compost..... But... progress is progress..... We buy cloth, make clothes, and watch the old ones fly off like at a frat party.
Milestone! We now have 100 units of compost from dead yeti, dwarf, human, and zombie bodies and turkey eggs! HOORAY! YAY! We fertilize our 1x5 plot, and get 50 fert! YAY! We plant that bitch into ratweeds. The month passes, and we get 100 ratweeds! YAY! we think....... We compost it and get... 20 compost!? ARE YOU SHITTING ME!? ARMOK TAKE YOUR SOUL YOU EVIL THING!
Next season rolls around, and the farm plot is down to 20 fert. I could have SWORN that the wiki said that it... oh... right.... 0% sunlight...... SHIT. (-20 fert for evil biome, and dry. -10 fert for ratweed, no sun) We can plant ratweed again, so we do. Another 100 units of ratweed. Composted... 20 compost added. Now at 40 compost.
We quickly realize that in order to sustain our 1x5 plot of farmland, we are going to have to CONTINUOUSLY subsidize it with dead turkeys and eggs. We completely forget about building the soil above 50 every 2 years, and produce sewer brew as the main alcohol, and live on turkey meat almost exclusively. We BUY all of our cloth, by selling turkey leather, and stone crafts. we savagely prune our population to survive.
Now-- see how that works now?