Why my station hero skill "farm improvement" has no effect on farm income?

If you have a hero with Farm Improvement active then it should increase the farm output. Try going into the management station building and 'recalling' the hero which will remove it from stationing and then check to see if the food production value changes. It may take a few seconds to adjust and it may be a small change. You can then go back to the building and station the hero again. See if it changes again.

If nothing changes then try using the support option in the game to contact the developers and report the issue.

What level is the hero's skill for farm improvement?