During any year in which marketing quotas for wheat are in effect, the producers on any farm (except a new farm receiving an allotment from the reserve for new farms) on which any crop is produced on acreage required to be diverted from the production of wheat shall be subject to a penalty on such crop, in addition to any marketing quota penalty applicable to such crops, as provided in this subsection unless (1) the crop is designated by the Secretary as one which is not in surplus supply and will not be in surplus supply if it is permitted to be grown on the diverted acreage, or as one the production of which will not substantially impair the purpose of the requirements of this section, or (2) no wheat is produced on the farm, and the producers have not filed an agreement or a statement of intention to participate in the payment program formulated pursuant to subsection (b) of this section. The acreage required to be diverted from the production of wheat on the farm shall be an acreage of cropland equal to the number of acres determined by multiplying the farm acreage allotment by the diversion factor determined by dividing the number of acres by which the national acreage allotment (less an acreage equal to the increased acreage allotted for 1966 pursuant to
section 1335 of this title) is reduced below fifty-five million acres by the number of acres in the national acreage allotment (less an acreage equal to the increased acreage allotted for 1966 pursuant to
section 1335 of this title). The actual production of any crop subject to penalty under this subsection shall be regarded as available for marketing and the penalty on such crop shall be computed on the actual acreage of such crop at the rate of 65 per centum of the parity price per bushel of wheat as of May 1 of the calendar year in which such crop is harvested, multiplied by the normal yield of wheat per acre established for the farm. Until the producers on any farm pay the penalty on such crop, the entire crop of wheat produced on the farm and any subsequent crop of wheat subject to marketing quotas in which the producer has an interest shall be subject to a lien in favor of the United States for the amount of the penalty. Each producer having an interest in the crop or crops on acreage diverted or required to be diverted from the production of wheat shall be jointly and severally liable for the entire amount of the penalty. The persons liable for the payment or collection of the penalty under this section shall be liable also for interest thereon at the rate of 6 per centum per annum from the date the penalty becomes due until the date of payment of such penalty.