you are right!

i did actually forget about that when commenting, and thanks for the added info!

however, that's not exactly what i was talking about:

assuming normal or better soil you need less work (i.e. time spent working the fields) per unit of nutrition when moving from rice->potato->corn because of yield.

so your pawns spend less time planting and harvesting, which results in higher overall colony productivity since they can do other stuff in-between, like cooking, cleaning, mining, etc.

you are correct in that you should choose which plant you use based on the soil first, and according to productivity second!

i just wasn't really considering soil quality when writing the comment...