Well, that nitrogen stuff, just looking at that first, seems to be entirely based upon looking at the plants once the problems have already occured.
In-game, this will probably need to be displayed as a text line, and it might seem a little odd, but if we go by that, we would come up with a scale like this:
"Plant leaves look healthy"/"Plant leaves are slightly pale"/"Plant leaves are showing slight yellowing and somewhat small"/"Plant leaves are yellowing, new leaves are progressively smaller, and show ruddy undersides"/"Plants are stunted in their growth, and are discolored yellow and red"
(keep in mind, this would show, even while fallow, and also, it would say "Plant leaves look healthy" even if it said plants are dying in other fields...)
This would be my mockup Phosphorous, I suppose:
"Plant stalks look healthy"/"Plant stalks seem slightly thin"/"Plant stalks seem slightly thin, with thin purple veins appearing"/"Plant stalks are thin, with purple veins, and a slight blueish leaf tint"/"Plant growth is stunted, with spindly thin stalks and purplish-blue veins and splotches on the leaves"
Potassium mockup:
"The leaf tips are healthy"/"The leaf tips are slightly yellowish"/"The leaf tips are yellowing"/"The leaf tips are yellow with browning splotches, and purple spots are appearing on the underside"/"Plant growth is stunted, the leaf tips appear burned and dark brown, with purple splotches on the leaf undersides."
Acidity would be more of a balancing act, even if we don't include over-fertilization in other aspects. Nitrogen fertilization (wether by crop rotation or by artificial fertilizers) often adds acidity to the soil, but if we use ammonia as a fertilizer, that would actually potentially be making soil too basic. According to wikipedia, you actually want your soil just very slightly acidic, so "neutral" is a little too basic, but that might be confusing, so I'll just ignore that part.
"The soil is too alkaline for proper growth"/"The soil is alkaline"/"The soil is slightly alkaline"/"The soil is faintly alkaline"/"The soil is balanced"/"The soil is faintly acidic"/"The soil is slightly acidic"/"The soil is acidic"/"The soil is too acidic for proper growth"
Oh, and hey, let's do water, too.
"The soil is moist"/"The soil is slightly moist"/"The soil is losing moisture"/"The soil is becoming dry"/"The soil is too dry to support farming"
Note, this isn't talking about having any specific nutrient or even water being possible to "over fertilize", which may or may not be in Toady's plans.
Additionally, the game might start reccomending yellow solution activities, the way that the game currently tells you that you need mud. For example, saying that legumes (or whatever fake plants we make up as nitrogen fixers in an ecology that isn't even based on photosynthesis, anyway) or ammonia fertilizer would help add nitrogen.
I'd also like to say, before we get locked into NPK+pH+water as our only nutrients of note, that, well, yes, we're still underground farming as much as anything else, here. Chemosynthesis would be a realistic (if potentially not particularly appetizing) means of theoretically unlimited underground nutrient creation via magma farming. Basically, just using some method of turning obsidian farming /
a pumice explosion into producing nutrients by crushing various igneous stones into some sort of powder that could be dumped into "farms" of shallow pools of microorganisms (or just dumping stones into water outright), and the creatures that live on them.
http://www.geo.uni-bremen.de/Ozeankruste/Research/Research_Weathering.htmhttp://en.wikipedia.org/wiki/ChemosynthesisReal life chemosynthesis is based upon things like oxidizing iron (which mafic magma flows are rich in, such as ones near the magma sea in this game), and especially hydrogen sulfide, which produces, as a byproduct, clumps of solid sulfur.
If we model this in-game, we could either use the megafauna that can survive off of deep vent chemosynthesis creatures as a food source directly (mmmmm... tube worms and abyssal crabs), or, presuming that eating a sulfurous life form would be too disgusting, we could fish them up, and use their carcasses as the organic base for fungus growth instead of using wood chips, as most modern mushroom farms do.
Once composted by fungi (whether edible or not), they could then be used as a base material for future underground farming. (Funguses are capable of growing off of other funguses, essentially to the point where absolutely every last trace of chemical energy has been consumed, so you just need to keep adding biomass in to replace the amount of biomass you take out.)
As had been said earlier in this thread, mushroom growth is often done simply by planting funguses onto a dead log, and waiting for mushrooms to grow. Even controlled-environment mushroom growth (that even take place in abandoned mines, no less) often uses sawdust as the base medium for growing mushrooms. Going to "Start your own mushroom farm" places, they are basically selling either wooden dowels as growth mediums, or a mash of some kind of cereal grain or a fruit mash.
In one of these, however, it does reccomend using a "fertilizer" of ammonia (that's NH
3, or a nitrogen fertilizer) early in the process.
Oh, and hey, while I'm at it, there's a British meat-substitute mushroom that goes under the brand name "quorn", that is used to replace chicken for those who think that soy beans aren't strange enough, and want to eat mushrooms as their meat replacement, instead:
Quorn, which I had never heard about until a Modern Marvels on, of all things, fungus. This stuff is apparently a non-mushrooming ground fungus that is grown in a vat of water that is fed with glucose and starch, which are largely carbohydrates you only get out of decomposing some photosynthetic or chemosynthetic lifeform (or something that ate one).
I would go into the subject of fertilizers, but I think this post is probably getting a little on the unweildy side, so I'll break it up into another post.