Substrate soluble salts consist of all the organic and inorganic components in the soil solution that will conduct electricity. These include the salts applied during fertilization, slow-release fertilizer, salts from poor quality water, residual fertilizer, dissolved salts from the media components, and compounds resulting from microbial decomposition of organic matter. Some fungicidal drenches also contribute soluble salts. Soluble salts is a fairly reliable measure of the nutritional status of a crops as long as the major source of salts is from the fertility program. Soluble salts is determined by measuring the ability of a sample solution from the substrate to conduct electricity.
Crops vary in their tolerance to soluble salts.
Seedling and rooted cutting are the most sensitive. Some crops such as African Violets and Azalea are particularly sensitive and should not be grown at high soluble salts levels. Recommendations are available providing optimum soluble salts ranges for most major greenhouse crops. Every greenhouse should purchase pH and soluble salts testing equipment. However, many growers only check soluble salts and pH when a problem is perceived.