The national allotment for wheat, less a reserve of not to exceed 1 per centum thereof for apportionment as provided in this subsection and less the special acreage reserve provided for in this subsection, shall be apportioned by the Secretary among the States on the basis of the preceding year’s allotment for each such State, including all amounts allotted to the State and including for 1967 the increased acreage in the State allotted for 1966 under section 1335 of this title, adjusted to the extent deemed necessary by the Secretary to establish a fair and equitable apportionment base for each State, taking into consideration established crop rotation practices, estimated decrease in farm allotments because of loss of history, and other relevant factors. The reserve acreage set aside herein for apportionment by the Secretary shall be used (1) to make allotments to counties in addition to the county allotments made under subsection (b) of this section, on the basis of the relative needs of counties for additional allotments because of reclamation and other new areas coming into production of wheat, or (2) to increase the allotment for any county, in which wheat is the principal grain crop produced, on the basis of its relative need for such increase if the average ratio of wheat acreage allotment to cropland on old wheat farms in such county is less by at least 20 per centum than such average ratio on old wheat farms in an adjoining county or counties in which wheat is the principal grain crop produced or if there is a definable contiguous area consisting of at least 10 per centum of the cropland acreage in such county in which the average ratio of wheat acreage allotment to cropland on old wheat farms is less by at least 20 per centum than such average ratio on the remaining old wheat farms in such county, provided that such low ratio of wheat acreage allotment to cropland is due to the shift prior to 1951 from wheat to one or more alternative income-producing crops which, because of plant disease or sustained loss of markets, may no longer be produced at a fair profit and there is no other alternative income-producing crop suitable for production in the area or county. The increase in the county allotment under clause (2) of the preceding sentence shall be used to increase allotments for old wheat farms in the affected area to make such allotments comparable with those on similar farms in adjoining areas or counties but the average ratio of increased allotments to cropland on such farms shall not exceed the average ratio of wheat acreage allotment to cropland on old wheat farms in the adjoining areas or counties. There also shall be made available a special acreage reserve of not in excess of one million acres as determined by the Secretary to be desirable for the purposes hereof which shall be in addition to the national acreage reserve provided for in this subsection. Such special acreage reserve shall be made available to the States to make additional allotments to counties on the basis of the relative needs of counties, as determined by the Secretary, for additional allotments to make adjustments in the allotments on old wheat farms (that is, farms on which wheat has been seeded or regarded as seeded to one or more of the three crops immediately preceding the crop for which the allotment is established) on which the ratio of wheat acreage allotment to cropland on the farm is less than one-half the average ratio of wheat acreage allotment to cropland on old wheat farms in the county. Such adjustments shall not provide an allotment for any farm which would result in an allotment-cropland ratio for the farm in excess of one-half of such county average ratio and the total of such adjustments in any county shall not exceed the acreage made available therefor in the county. Such apportionment from the special acreage reserve shall be made only to counties where wheat is a major income-producing crop, only to farms on which there is limited opportunity for the production of an alternative income-producing crop, and only if an efficient farming operation on the farm requires the allotment of additional acreage from the special acreage reserve. For the purposes of making adjustments hereunder the cropland on the farm shall not include any land developed as cropland subsequent to the 1963 crop year.