Are nutrient level and substrate-EC too low?

Fertilizer levels in the media can be measured using an electrical conductivity (EC) meter. A low substrate-EC means low nutrient levels are available in the growing medium. This may lead to “hungry plants”, with symptoms of yellowing (chlorosis) and stunted plants. This article discusses causes and solutions for low substrate-EC. Test corrective actions on a small group of plants first, and 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 low EC issue. Target EC ranges vary between testing methods and crop types. EC is often lower in plants grown with controlled-release fertilizers (CRF) compared with water-soluble fertilizers (WSF), or in young plants growing in small containers. So a low substrate-EC is not necessarily an issue if plant growth is fine.

Plant demonstrating low EC

Evaluate plant appearance 

Typical leaf symptoms of low nutrient level are a pale green color, but in some crops there may be red coloration or interveinal chlorosis. Mild nutrient deficiency may cause large soft leaves, whereas stunting occurs with severe deficiency. Other causes such as high pH or deficiencies in specific nutrients such as magnesium, nitrogen, or phosphorus can give symptoms similar to low EC, so run an onsite soil test.

Plant demonstrating low EC

Identify the causes of low EC

It can help to consider nutrient level in a container as a “bank account”. A low salt level can result from a low initial nutrient level (for example, no pre-plant fertilizer). Nutrient deposits from fertilizer may be less than withdrawals over time by plant uptake or leaching (washing out of nutrients). Was inadequate starter fertilizer applied before planting? Is applied fertilizer concentration less than plant needs and if so, why (fertilizer injector not working, mixing or application error, crop management plan needs to be changed to increase fertilizer rate).  Are plants being leached too much and if so, why (inefficient irrigation system, more worker training required)?

Extreme low nutrient level

Corrections for low substrate-EC

  • If pH is high apply an acid-reaction (high ammonium) fertilizer such as 20-10-20. Otherwise if pH is on target or low use a basic-reaction (high nitrate) fertilizer such as 15-5-15.
  • If plants are not stressed and you are using a WSF, increase fertilizer concentration by approximately 50 ppm.
  • If a rapid correction is needed, drench with 200 to 400 ppm N with a blended WSF. Fertilizer applied = concentration x volume.  Therefore, apply a high volume with leaching to replace soil solution. Rinse foliage with clear water after fertilizer application
  • Avoid excess leaching (more than 10%). Consider CRF if crops are exposed to rain and uncontrolled leaching.

Nutrient level in a container is like a bank

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.