Upon whom is the Ushr due if a person usurps land, cultivates it, and harvests the crop?

Primary text

If a person usurps land, cultivates it, and takes the produce, the Ushr is incumbent upon the usurper because ownership of the crop, upon which the obligation stabilizes, was established in his possession. If the landowner seizes the crop before the grain fully hardens (*ishtidad al-hubb*), the Ushr is due from the landowner. If the landowner seizes it after the grain has hardened, there is a valid opinion that the Ushr is still due from the landowner because the seizure relates back to the beginning of cultivation. Alternatively, the Ushr may be due from the usurper as he owned the crop at the time the Ushr became obligatory, which is when the grain hardened.