The regents of the agricultural college of New Mexico [New Mexico state university] are further authorized and empowered after proper application and hearing to define such zone or zones and to further define neutral zones between such above-mentioned zones, and to provide that within the neutral zones no plant or plants, fields or plots of plants of a given strain, species or variety, may be grown to maturity or to the state in which buds of the said plants are produced. The purpose of such said neutral zone being to avoid the possibility of cross-pollination or mixing and thereby rendering valueless what would otherwise be pure strains of seed, provided that the said regents may at their discretion permit that within such neutral zones varieties, strains or species not related to crops permitted to be grown within prescribed zones may be planted for the purpose of seed production; provided that such varieties or species are of the kind which will not cross-pollinate or otherwise render impure, pure strains grown in adjoining zones as defined by the said regents.