Maybe I am missunderstanding what you said.

Here's what I understood....you rented land knowing it might sell.  You begin to prepare for the next crop year with tillage and application of manure.   It has sold.  The owner (old, or new owner?) has agreed to reimburse you for the expenses you have put into the land for this crop.  You are asking only about the manure.

If that is not right, correct me....maybe my opinion will change.  

Right now, my opinion would be that if it were a normal ag lease, you would be entitled to farm it until the next end-of-lease date.  If there were added provisions to enable it to be sold sooner  without encumbrances,  it would depend on what those provisions stated. 

Since they are paying for your tillage expenses,  I would not understand why they would do that and refuse to pay for the fertilizer which you applied.  I don't see why there is any difference between commercial or manure, either way if they are reimbursing. 

I don't know if they are obligated to pay, but you have said that they are paying....with that given, I see no reason to pay for some and not all.