Ok, scratch my last post, it wasn't good. It didn't really allow for crop rotation, now I see it. I'll try something else... Considering you want crop rotation, there are many ways to implement it, not just one. Let me demonstrate why I'm worried about the NPK+Ph+Biomass+Water system.
This is how I understand it, correct me if I'm wrong:
You could let the AI handle it automatically (like in Fieari's example, a nice post by the way!), but you some of you seem to dislike the notion. So let's do everything manually.
There are several soil properties being tracked (6 if I count correctly). All of these
continually change (depending on what you grow and what's happening to the soil) and affect the crops. Let me repeat it: you have
six separate, continually changing variables for something as critical as farming. This sounds like trouble. It means the player will regularly have to check their farms to see if something important has changed... having six variables, it's very probably that something
will have changed every few weeks or months. The player needs to step in and order more water, fertiliser, perhaps change crops or do something special. Every few months.
Translation: we have added a menial uninteresting task to the game that needs to be done regularly and can't be skipped. Awesome.OK BUT... the player can set the system once and then let it work indefinitely by itself, right? So they can, for example, spend 30 minutes browsing through the nutrient numbers, game wiki, farming tables, crop properties, etc. and after a lot of difficult calculations come up with a clever system that will keep all the six variables on desired levels without them drifting away in any direction... but only if they hadn't made any mistake in any of the million calculations. If they had, the soil properties will change after a year or two and whole the process must begin anew.
BUT! Let's say I'm very clever, I'm willing to spend a day learning all about the nutrient system, then I'm willing to to spend half a day calculating the numbers AND I don't make any mistake. In the evening, after a hard day's work, I have a nice small wheat farm that's able to grow tasty grain for years, and with crop rotation set so that the soil properties won't change. Victory!
Or not?
Two years into the game I realise my wheat field is to small to feed my fortress and decide to create a new one on the opposite side of the river. But alas! The soil there has different properties! I can't use my former calculations because they would make the soil quality drift away. I need to calculate it from scratch. Fortunatelly, I'm very good at it and with a small aid of a calculator manage to build my field in mere 15 minutes.
All is well until another year into the game I decide I will simply import all my food and will grow rope reed insted. I switch both my farms to grow rope reed, only to find out rope reed has different effect on the soil and makes my farm become too phosphorous over time. I need to scratch my former calculations again, and begin anew. Twice, because I have two different fields.
Swearing never to change crops I again, I play on. Another year in the future, a plague comes and kills all my rope reeds. Which is fine, I have many in reserve. What's worse is that the plague
changed two of the six properties, completely ruining all my former plans. I need to run all calculations again! Cursing heavily, I turn Dwarf Fortress of and decide never to play it any more.
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So did I get it right?
I'd be very happy if you disprove my theory and explain why the NPK+Ph+Biomass+Water is much less difficult. Because I'd really hate to have the above in the game.
(EDIT: I also doubt historical people spent their evening in the company of NPK+Ph+Biomass+Water tables, trying to come up with a way to make the land less phosphorous or perhaps decrease its pH. Hell, they didn't even know there's something like phosphorous and pH. Their farming system was "the land is good", "the land could be better", "the land is bad, let's try planting some legumes and hope for the best". If they could use such a simple system, why can't I?)
(EDIT2: Let me also say I've grown up on a village myself. My grandma has a large garden and has been growing lots of different vegetables over her life. If I asked her what nitrogen, phosphorous, and potassium are, she wouldn't now. All she does is water her garden, weed it, and sometimes buy use a general "fertiliser". Yet! A miracle! The garden lives, the vegetables grow, and the soil isn't getting too acidic or whatever.)
As for 'challenges', easy and challenging are mutually exclusive, you can't have challenges to keep your dwarves from starving to death, if it's always easy to keep your dwarves from starving to death.
Oh... when will people learn and stop doing this logical leap? Easy controls =/= easy game with no challanges. Difficult controls =/= fun game.