I am quite sure you can get out of most any contract. the thing is can you afford it.  May be a penalty, if you are normally a good customer or seller they may work around the delivery problem. They can always or at least most times buy off the board and replace your grain.  Trouble is you will have to make up the difference, incuding all delivery charges etc. Call a neighbor and see what it will cost you to get them to fill your contract. Then you will know. Just remember the next time when they want to cancel.

  I would do whatever it takes to deliver it.