Variability of soluble salts using different extraction methods on composts and other substrates

Soluble salts represent dissolved inorganic ions in solution and are typically measured in terms of electrical conductivity (EC). Often soluble salt measurements from different studies or laboratories cannot be cross-referenced or there is much confusion when comparing these results. The soluble salts from 13 composts and horticultural substrate materials were extracted using six different methods: saturated medium extract; pour-through, a water displacement method; and water suspensions using various ratios (by volume) of water:substrate (1:1, 1:2, 2;1, 5:1). EC ranged from 0.1 (peat and perlite) to 23.1 dS m⁻¹ (turkey litter compost). A linear regression model was developed to allow cross-referencing between extraction methods of measurements of soluble salts concentration of the composts and substrates.