Mechanical Support Materials

A large variety of both organic and inorganic materials have been used to formulate the synthetic soils used for mechanical support in hydroponic systems. Commonly used organic materials include sphagnum moss, peat, manure, wood, and other plant residues. Sphagnum moss, the shredded, dehydrated remains of several species of moss in the genus Sphagnum, is harvested for the purpose of producing synthetic soil. "Peat" is a term normally used to describe partially decomposed remains of wetlands vegetation that has been preserved under water. Peat moss is the only type of peat suitable for synthetic soil mixes. Peat moss is harvested from peat bogs, dried, compressed into bales, and sold. Animal manures are almost never used in commercial synthetic soil mixtures because they require costly handling and sterilization procedures.

Wood residues such as tree bark, wood chips, shavings, and sawdust are generally produced as by-products of the timber industry. A variety of other plant residues, including corn cobs, sugarcane stems, straw, and peanut and rice hulls have been substituted for peat in synthetic soil mixtures where there is a supply of these materials.

Commonly used inorganic materials include vermiculite, sand, pumice, perlite, cinders, and calcined clay. Vermiculite is a very lightweight material produced by heating mica to temperatures above 1,090 degrees Celsius (nearly 2,000 degrees Fahrenheit). Sand is a preferred material for formulating synthetic soils because it is inert and inexpensive but very heavy compared to other commonly used materials. Pumice, a natural, glasslike material produced by volcanic action, provides a good inert supporting material when ground into small particles. Perlite, a porous material that will hold three to four times its weight in water, is produced by heating lava at temperatures above 760 degrees Celsius (1,400 degrees Fahrenheit). Cinders are derived from coal residues that have been thoroughly rinsed to remove harmful sulfates. Calcined clay is derived from the mineral montmorillonite baked at temperatures above 100 degrees Celsius.

See also: Fertilizers; Horticulture; Nutrients; Nutrition in agriculture.

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