Some more things I discovered. plant nutrient levels are based off of "nutrient grids" I guess I'll call them. they're 4x4 grids that start on x,y coordinates that are multiples of 4 (1,1 - 4,4, next grids would start on 5, 9, 13, 17, etc both x and y)
all plants within these grid add their nutrient drains to all of the soil within that particular grid. exactly how the drain works exactly I'm still working on, but it culminates in plant growth slowing down, stopping, or dying altogether.
a quick and dirty fix for this is to make crop strips. this entails 1 wide by however long you want crop lines. this ensures that there is only 4 plants causing a drain on the grid for any grid you would happen to be in.
the most efficient way space wise (arguably) would be to find a 4x4 grid smack in the middle of 4 of these nutrient grids and then making that into a farm this would ensure that no more than 4 plants drain on any grid. the downside is that you would have to place your next 4x4 farm outside of all 4 of those grids, etc.