The trustee  or trustees (whomever was given the authority to make decisions for the trust) can decide who may or may not enter the property. The trust is its own legal entity--its own "person" if you would. Just as a person (or business) could refuse to let you on their property, so, too, can a trust refuse to let you on the property. So if the trustees will not let you enter, if you do, you will be trespassing and could face criminal charges.If they won't voluntarily let you on the land, your only option would be to file a lawsuit against the trust in chancery court (a part of county court which deals with issues involving "fairness" rather than clear legal rights and which also focuses on granting court orders to do things, not monetary compensation) and seek an order allowing you to retrieve the item. The court could weigh the terms of the will vs. the trust, look to the equities or fairness, and *could*--but is not required to--allow you to access the item, though it could put conditions on you doing so (e.g. scheduled in advance; a witness from the trust to what you are doing; inspection of anything you find, to make sure it's *only* what was willed to you; you posting a bond or escrowing money to pay to restore/repair any damage you do in digging; etc.).