Here's an interesting piece, via grist, on the problems of using "carrots". I'd extend the problem to conservation measures on farms. If you have, as you do, a range of farmers, from those who are operating responsibly (i.e., taking measures to reduce erosion) to those who are not, issuing carrots poses big problems. Either you give carrots to everyone who meets a standard, thus not getting much bang for your buck because you aren't changing the behavior of the good farmers, or you give carrots only to those bad farmers who become good, which is unfair to those who have been good all the time.
See the Bible and the prodigal son for the resentments this can cause.