Are salt level and substrate-EC too high?

Salt levels in the root substrate can be measured using an electrical conductivity (EC) meter. A high substrate-EC may result from excess fertilizer or contaminants such as sodium and chloride in the irrigation water. High EC leads to salt burn to plant roots, and toxicity symptoms in the foliage. This outline discusses the causes and corrections of high substrate-EC. Test corrective actions on a small group of plants first, and as a long-term strategy rely on prevention rather than cure.

Test substrate-EC

Test substrate-EC and pH using a standard procedure and a calibrated meter to confirm it is a high EC issue. Target EC ranges vary between testing methods and crop types. Evaluate plant appearance. Typical symptoms of high salts are stunted overall growth, dark green and thick leaves, marginal burn and yellowing on older leaves, and limited root growth or damaged root tips. Other causes such as pesticide phytotoxicity or low pH can give symptoms similar to high EC, so run an onsite soil test and evaluate crop history.

Plant demonstrating high EC

Identify cause of high substrate-EC

  • Consider salt level in a container as a “bank account”. A high salt level can result from a high initial salt level, or salt deposits over time exceeding withdrawals. The deposits may come from salts contained in the irrigation water, water-soluble fertilizer, media components, or slowly soluble or controlled-release nutrients. Withdrawals are mainly through plant uptake or leaching (washing out of nutrients).
  • Identify the causes of high EC. Was too much starter fertilizer applied before planting? Is applied fertilizer concentration higher than plant needs? Are salts coming from irrigation water (a likely cause if water EC is above 0.75 mS/cm)? Is more leaching required (or can this be avoided by using less fertilizer)?

Plant demonstrating high EC

Roots demonstrating high EC

Corrections for high substrate-EC

  • If the high EC was caused by excess fertilizer, switch to clear water irrigation until EC drops to the acceptable range. If plants are already showing stress symptoms, leach out nutrients by applying excess water with at least 50% leaching fraction (half of the water volume applied leaches out the bottom of the container). After EC correction, reduce applied fertilizer rate (for example, by 50 ppm N if using water-soluble fertilizer).
  • If the high substrate-EC results from non-fertilizer ions such as sodium or chloride, leach with clear water with at least 50% leaching fraction to remove the excess salt, and leach a second time with a complete fertilizer at a moderate rate to reestablish the nutrient balance.
  • If high EC resulting from over-application of fertilizer is a regular occurrence, change your fertilizer management plan in order to reduce costs, crop losses, and run off of fertilizer into the environment.

Nutrient level in a container is like a bank

What to avoid

Avoid the combination of high substrate-EC with low substrate-pH: this practice could result in high deposits of both macronutrients (e.g. N, P and K) and micro-nutrients (e.g. iron and manganese), resulting in micronutrient toxicity for iron-efficient crops (like geraniums and marigold).

For more information: Contact authors Jinsheng Huang and Paul Fisher of University of Florida IFAS Extension, and Dr. Bill Argo of Blackmore Co. Thanks to our Floriculture Research Alliance at University of Florida sponsors including A.M.A. Plastics, Blackmore Co., Everris, Fine Americas, Greencare Fertilizers, Klasmann-Deilmann, Pindstrup, Premier Tech Horticulture, Quality Analytical Laboratories, Sun Gro Horticulture, and leading young plant growers. The University of Florida does not endorse any product, and our research focuses on quality testing on these and competing products to assist grower success. June 30 2015.