Soil amendments are added to a planting medium in order to provide plants with various nutrients.
Guano. Dried poo. May be either from bats or birds. Guano is available in high Nitrogen, high Phosphorous and balanced formulations. Guano will burn your plants, so use conservatively.
Worm Castings. Worm poo. An excellent source of micronutrients. Also, a supplemental source of Nitrogen. Castings ought to be in every soilless mix. They will not burn your plants, and, when cut with perlite and vermiculite, make a fine medium in their own right.
Bone Meal. As the name implies, this is ground up bones from the slaughter house. Bone meal provides phosphorous. Will attract animals to your grow if used outside. Will attract pets if used inside.
Blood Meal. Again, made from animal blood on the slaughter house floor. A source of nitrogen. Also, attracts animals to your grow. Particularly odiferous. Blood meal will burn your plants, so use conservatively.
Kelp Meal. Made from dried and ground seaweed. If made from ascophyllum nodosum, provides a growth hormone which promotes rapid growth of both roots and foliage. Also contains trace elements and enzymes.
Perlite. A non-porous volcanic byproduct, perlite is pH neutral and improves the drainage of planting mediums.
Vermiculite. A porous volcanic byproduct, capable of nutrient and cation exchange.
Dolomite lime. Frequently used in planting mediums to offset acidity, that is, lime raises pH. Dolomite lime is slower acting and more buffered than hydrated lime.