New Farmland Paradigm
The current situation with the farm fields should be remedied. There have been suggestions for a farming queue or something like that, but after much internal discussion, we've come to somewhat of a consensus.
1 or more of the following may need their own tickets.
Farm fields are infinite, no matter where they are placed.
Gatherers have a "diminishing returns" feature, in that for each additional gatherer after 1 drives down the gather rate of all of them, to the point that it is more efficient to build a 2nd farm field by the time the gatherers get to 5.
Update: Both of these were committed in r13616.
There should be a set of terrain textures on the terrain that give a big gather boost if farm fields are built there. Anywhere from +50% to +100% gathering rate, depending on playtesting. These "farmland" areas then become areas of contention for players to fight over. The player can choose to seed farms anywhere they wish, but they will be considerably more efficient if placed on farmland.
There can also be an overlay for the farm field when the player is choosing where to place it. This will explicitly tell the player whether they're placing the farm field on efficient farmland or non-efficient land.
Green - When the farm field is being hovered within the farmland terrain adequately (and will receive the efficiency bonus when built there).
Yellow - When the farm is being placed on non-farmland (and will get no efficiency boost).
Red - When obstructed.
Farmland terrain textures in Atlas
A similar technique should be used for farmlands as is already being used for 'city tile' or 'road' textures. Each biome will have its own farmland texture. It'll get placed in a new "Farmland" tab in the terrain panel by an XML file (exactly like what is done with city/road textures). If you don't know what I'm talking about with the city/road textures, then please look in mods/public/art/textures/terrain/types/biome-mediterannean/medit_city_pavement.xml for an example. That file gives the medit_city_pavement terrain its properties and places it in the "city" tab in Atlas.