The only way I see anyone being able to offer yield on corn is if the company/bank/govt issuing the yield has control of a sustainable energy source and are able to mine the corn for cheaper than the value of the corn.  

That's a very high hurdle rate and I don't think any of the current public miners are achieving that now.  It's possible but very difficult.  A bank in metro New York definitely is not creating that value.  It's going to be some stranded energy source in a desolate area generating electricity for basically free.