Thanks for sharing that data model PDF @Ludwig! Very helpful to see how you’re modeling things. It looks great!
One small suggestion: In your seeding, input, medical, and harvest logs I notice that you include two assets in the log’s asset field (eg: “W-Rapeseed Field A Plant 24/25” plant asset and “W-Rapeseed Otello KWS Seed” seed asset in the seeding log). This may have unintended consequences. For example, seeding logs are “movements” by default, and any assets referenced in the asset field will be “moved” by them. The asset field is generally meant to be used for “the assets that are receiving the action” (as opposed to the location field which is “where the action took place”, or the equipment field which is “the equipment that performed the action”).
It makes sense that you would want to reference the seed, material, and product assets the way that you are, but I think it would be better to move them somewhere else.
One way to do it is to reference those “secondary” assets from the “Inventory Asset” field on your quantities. This would also allow you to start tracking inventory for those seed, material, and product assets.
For example, you could reference the “Innovert Rapeseed Material” asset from the “Price” quantity on that log, and record it as an inventory “decrement”. Then, you can also record Purchase logs that “increment” the inventory of the material asset.
These are both great ideas, and probably each warrant their own dedicated forum topic! 
The gross margin calculation will require establishing a standard convention for recording costs and sale prices. If you haven’t already, check out this forum topic about conventions:
I’m sure there are others that would benefit from nutrient balance optimization features too.
There are two ways to go about feature development in farmOS: custom or general. I always try to encourage designing general solutions that can be built and maintained by the community. But sometimes custom solutions are necessary to get the job done in the short term.
To understand generally how stuff gets built, read this:
We also created a “Jobs Board” category a while back, although it hasn’t had much action 
- if you want to offer sponsored development of a custom module (which could be a start to a community module), you can consider posting there! Jobs Board - farmOS