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