(debtors entered into lease of cropland and hay ground with landlord’s conservator with annual rent payable in April and December; debtors filed bankruptcy in November, and the following March rejected the lease; conservator requested full amount of December rent be treated as administrative expense and court held that rent due post-petition and pre-rejection could be allowed as an administrative expense only for the time of the debtor’s post-petition use of the premises with interest at 12 percent per annum (as provided for in lease for unpaid rent).