It is declared to be the policy of the Congress that, in the opening to entry of newly irrigated public lands, preference shall be given to families who have no other means of earning a livelihood, or who have been compelled to abandon, through no fault of their own, other farms in the United States, and with respect to whom it appears after careful study, in the case of each such family, that there is a probability that such family will be able to earn a livelihood on such irrigated lands.