Reducing field upkeep

Hi there, this is probably going to sound super noobish but I'm new to farming and a lot of guides are telling me to use wood choppings in order the reduce their upkeep. Whenever I try to do this, however, the choppings just don't register with the field. I'm left clicking the woddchoppings then right clicking the field, but the choppings are never removed from my invent, and the upkeep is never reduced. Is there something I'm just not getting? I've tried tilling a few more fields but it just never seems to work.
Do I have to use my humus first?
Do I alternate humus with the wood choppings?
Is there some secret method that I'm completely oblivious to?
Thanks for any help!
Do I have to use my humus first?
Do I alternate humus with the wood choppings?
Is there some secret method that I'm completely oblivious to?
Thanks for any help!
