For me, I just learned civil service, but I still cannot make farms chained to other farms next to a lake. The worker ability remains "greyed" out, although the "red" message saying "requires civil service" is now gone
The only thing I can think of, is that I never bothered to learn archery (due to early special unit) or horsemanship (due to no local horse sources early). Does the effect of Irrigation (or Biology perhaps) require more techs than just the one listed?
For example, in another game, I couldnt learn philosophy until I learnt meditation - fair enough, but the lines dont show the direct requirement. Could something like that be happening with irrigation/biology effects?
ew