Chapter 7 - Inorganic and Synthetic Organic Components of Soilless Culture and Potting Mixtures

Abstract

This chapter covers the most representative and most widely applied media out of the numerous existing substrates. In this chapter substrates are grouped into two categories of materials: (1) “inorganic substrates” are classified as natural unmodified materials (sand, tuff, pumice) and (2) “synthetic substrates” consist of processed materials (such as stone wool, perlite, vermiculite, expanded clay, zeolite, and foamed glass). Synthetic organic materials include substrates, such as phenolic resin or polyurethane. Important properties of the substrates include their chemical activity and surface charge. Therefore substrates are characterized as active (e.g., peat, tuff) or semiinert (e.g., stone wool and sand) materials. The description of each substrate includes information on production and origin, and general information about their applicability as growing medium. The physical characteristics that include BD, water retention, and hydraulic conductivity are provided, as they are essential for proper irrigation management. The chemical characteristics such as composition, stability as affected by pH, cation exchange capacity (CEC), pH, and salinity are discussed as they are required for proper fertilization and nutrient management. Information on substrate sterilization is provided, as disease control is a major factor for the reusability of substrates. Information on waste treatment is also presented because today the potential for environmental contamination is a central issue in intensive soilless cultivation. In practice the optimal substrate is produced as a mixture of several components, which are commonly selected through trial and error by growing plants in a series of mixtures. Replacing this trial and error approach with physicochemical relationships for prediction of mixture behavior from well characterized constituent properties would significantly advance soilless culture production and eliminate costly mistrials. Based on this premise the prevailing physical and chemical properties of substrate mixtures are reviewed and discussed in this chapter.