Petitions for including additional territory within an existing district may be filed with the state soil conservation committee. The proceedings provided for in this part in the case of petitions to organize a district shall be observed in the case of petitions for inclusion. The committee shall prescribe the form for such petitions, which shall be as nearly as may be in the form prescribed in this part for petitions to organize a district. Where the total number of landowners in the area proposed for inclusion is less than twenty-five (25), the petition may be filed when signed by a majority of the owners of the area, and, in such case, no referendum need be held. In referenda upon petitions for inclusion, all owners of land lying with the proposed additional area shall be eligible to vote.