A pH change of 1 unit means a 10-fold increase or decrease of acidity. Most composts have a pH of between 6 and 8. Each specific plant species requires a specific pH range. Based on the amount of compost applied, as well as it's pH, its addition can affect the pH of the soil or growing media. Therefore, to estimate the effect, which in turn will affect maintenance practices or system management, pH is a necessary parameter of which to be aware.
Soluble salts refers to the amount of soluble ions in a solution of compost and water.
The concentration of soluble ions is typically estimated by determining the solution's ability to carry an electrical current, i.e., electrical conductivity. Plant essential nutrients are actually supplied to plants in a salt form. Plant species have a salinity tolerance rating and maximum tolerable quantities are known. Excess soluble salts can cause phytotoxicity to plants. Compost may contribute to, or dilute, the cumulative soluble salts content of a growing media or soil.