2. Horizontal Silos
All silage storage structures which have the greatest dimension in the horizontal plain may logically be referred to as "horizontal" silos. Basically there are three main types of horizontal silos:
(a) Trench - a silo that is built into the ground by digging a hole or "trench" below the natural grade line (sometimes referred to as a "pit" silo);
(b) Bunker - a silo that is built above the natural grade line; and
(c) Stack - essentially a pile of silage where no structural walls are used to contain the material.
Both trench and bunker silos may have walls constructed of wood or concrete. The selection of types of walls and materials will depend on economic considerations of capital and annual cost, availability and durability of materials, types of silos, and personal preference.