I would not take the chance of going on the land at this point in time.  If the owners' permission was verbal and there is a lease in place for the land then the lease will over ride the verbal permission.  But even if there is written permission to go on the land it could violate the rights of the tenant and their lease and subject you and the owner to being sued.  Even if the crops are not in season you and the 4 wheelers could indeed cause damage to the soil thereby compromising the investment the tenant has put in to the land.  This guidance assumes that  tenant has control under the lease.  Without seeing it and knowing more about the rights of each party I think it is best for you to steer clear.