Why Your Controlled-Release Fertilizer Didn't Work

Published online: Mar 29, 2018 Articles, Fertilizer Nelson Gonzalez
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Nelson Gonzalez, territory/key account manager at ICL Specialty Fertilizers, discusses the top 10 reasons controlled-release fertilizers may not be performing as growers expect.
  1. Fertilizer displacement. If you incorporate your fertilizer and are bumping a smaller container to a larger container, take into account the amount of media and fertilizer that is being displaced when the smaller container takes the place of what would have been fresh media and new fertilizer. Not doing so will more than likely result in a lower fertilizer dose per pot and shorter longevity for your CRF.
  2. Not choosing the proper longevity. Choose a longevity that is too short, and it will not go the distance. Choose one that is too long, and you may experience slow growth, especially up front. The longevity you choose for your crop should be one that provides that crop with the proper nutrition throughout the growing cycle, and it should be based on the needs of that particular crop.
  3. Not using the proper formulation. In my opinion, the only way to figure this one out is by trialing and discovering which product is truly best for your crops under your growing conditions and practices. The practices and materials someone else uses to grow a crop more than likely are not the same as yours. I could give you all the ingredients you need to make a great-tasting chocolate cake, but that doesn’t mean yours will taste the same as mine. (In all honesty, yours will probably taste better than mine.)
  4. Not choosing the proper rate. Get this wrong, and it will affect your longevity. More often than not, growers will use a lower rate than what is necessary. I understand we’re trying to cut cost. If you use a low rate and experience high temperatures, you can be sure that your CRF will not go the same distance as if you experience mild temperatures. Don’t cheat yourself; a little more CRF per pot is only a couple additional pennies per pot.
  5. Method of application. Whether you top-dress, sub-dress, dibble or incorporate, be sure you use a method of application that is best for your crop and your growing practices. Contact your chemical rep for help on this one.
  6. Over-irrigation. Although the release of controlled-release fertilizer is based off of temperature, over-watering could lead to excessive amounts of nutrients leaching from the container, making them unavailable to the plant. Monitor and evaluate your irrigation practices.
  7. Too high or too low media pH. Monitor the pH of your crop. A high pH could restrict the absorption of micronutrients that are necessary to the success of your crop, and a low pH could cause toxicity, reduced plant growth and even an increased probability of micronutrient antagonisms.
  8. CRF and media storage. Be sure your CRF is properly stored in a dry environment. If you are incorporating your CRF into the media, be sure the media and CRF are maintained dry and used as quickly as possible. The fertilizer will start to absorb water in the media and begin to release fertilizer once incorporated, leading to high ECs in the soil the longer it is stored--especially toward the bottom of the media pile, if it is watered or allowed to receive rainfall.
  9. Green bark. If your growing media contains green bark or wood, it can easily rob part of the nutrients provided by the CRF, leaving the plant with less feed.
  10. Micronutrient package. I’ve done a video on this one in the past. Make sure you are using a quality micronutrient package with some longevity to it. Not doing so may increase your likelihood of micronutrient deficiencies.