Can i create an improvment with a food bonuse on land ? In the editor, i see only a food bonuse on water.

unfortunately, you can't boost food production on ANY land tiles with an improvment, which sucks.... I had some great ideas of how to use such improvements to keep the AI and human players from clear-cutting all the forests, draining all the swamps and bulldozing all the rain forests, but unfortunately that was impossible to do with improvements.

I WAS able, however, to get the same effects by making swamps irrigatable (symbolizing aquaculture), and jungles and forests mineable (symbolizing managed forestry) to achieve the same effect ;)

you can make a recource and place it on every tile you want improved...

but then he won't get bonuses from other recourses!