Public lands which it is proposed to irrigate by means of any contemplated works shall be subject to entry in tracts of not less than forty nor more than one hundred and sixty acres: Provided, That whenever, in the opinion of the Secretary of the Interior, by reason of market conditions and the special fitness of the soil and climate for the growth of fruit and garden produce, a lesser area than forty acres may be sufficient for the support of a family on lands to be irrigated under the provisions of the Act of June seventeenth, nineteen hundred and two, known as the reclamation Act, he may fix a lesser area than forty acres as the minimum entry and may establish farm units of not less than ten nor more than one hundred and sixty acres. Wherever it may be necessary, for the purpose of accurate description, to further subdivide lands to be irrigated under the provisions of said reclamation Act, the Secretary of the Interior may cause subdivision surveys to be made by the officers of the reclamation service, which subdivisions shall be rectangular in form, except in cases where irregular subdivisions may be necessary in order to provide for practicable and economical irrigation. Such subdivision surveys shall be noted upon the tract books in the Bureau of Land Management, and they shall be paid for from the reclamation fund: Provided, That an entryman may elect to enter under said reclamation Act a lesser area than the minimum limit in any State or Territory.