After emergence, inoculation is risky, difficult, and expensive. Many strains of rhizobia are present in soil, and some may form nodules on alfalfa roots, but not all nodules fix nitrogen. Effective N-fixing nodules on alfalfa are generally pink to deep red on the inside and can fix several hundred pounds of nitrogen per acre each season. Specific rhizobium bacteria for alfalfa assure effective nitrogen fixation by new stands. Together they convert atmospheric nitrogen into a form available to plants if effective nodules are present.
Inoculation is nothing more than mixing bacteria with the seed before planting.
Dry inoculant can be mixed with seed, but it is difficult to assure good mixing and to avoid much of the inoculant from falling on the ground some distance from the seed. Stickers help nodule forming bacteria adhere to seed. Excellent commercial preparations of stickers and rhizobium are available from inoculant manufacturers. For best results, follow the manufacturer's instructions. One pint of the sticky mixture provides sufficient sticker for a bushel of seed.