Maybe the wisdom of Solomon should be borrowed: let's cut somebody in half.
Nay, it looks guilty on both sides... funny how we humans like to do that. I'd still say that Farmer A (He's the Owner) is MORE wrong than Farmer B- laziness not being well smiled on in medieval times. Not to mention attempting to get profit from another man's labour. Farmer B (the Planter) seems to be guilty- in the main- of being overzealous. His statement of not having time to consult the Eorl, coupled with the relative newbieness of the Eorl (one month is NOT a long time), it seems likely to me that his offence is primarily of the "slap on the wrist" variety.
And I agree with Folwren concerning North American law. In both pioneer America and pioneer Canada, buying unbroken land from the government was cheap- but it didn't belong to you for X number of years unless you worked the land all those years. (The number of years, amount of crop, as well as other stipulations like living on the land, varied, I believe.)