Silicon Recommendations for Citrus

Josh McGillCold Hardy, Nutrition

A University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) researcher recently wrote an article about silicon that included recommendations for its use. The article by Muhmmad Shahid, assistant professor of horticulture, appeared in the UF/IFAS Cold Hardy Citrus Connection newsletter. Silicon’s benefits may include improved yield, a strengthened root system and tolerance to abiotic stress, including cold. Excerpts from Shahid’s article follow: 


Silicon can be applied in different ways to plants. It can be directly applied by incorporating it in the soil if using a powder form. It can be dissolved in water to make a solution that’s applied to the soil through sprinkler, drip or overhead irrigation.

Seeds and cuttings can be treated with silicon through dusting, soaking, misting and dipping. The silicon application rate depends on plant bioavailable form of silicon in the product, the application method and plant type. Although silicon phytotoxicity is uncommon, it is suggested that growers run a small test before using silicon fertilizer on a large scale.

Some plant species/varieties respond well to foliar application, while root-zone application or the combination of both (foliar and root zone) works well for others.

Crop-specific research is needed to determine theoptimal level of silicon for getting maximum beneficial effect in terms of growth, yield, disease resistance and abiotic stress. In general, the recommendations are:

  • 50 to 100 parts per million (ppm) for foliar application
  • 50 ppm for regular fertigation or 100 ppm once a week
  • 1 to 6 tons depending upon soil pH for soil incorporation in powder form

Liquid silicon fertilizer is formed by dissolving silica (SiO2 or sand) in lye, so the final solution is very alkaline with pH of 11 to 12. It is suggested that the pH be adjusted to 6.5 to 7 before foliar or fertigation application.

Concentrated silicon fertilizer should not be used with other regular nutrients because silicates will polymerize to form gel-like materials. Conventional fertilizer (N, P, K) and silicon fertilizer application should be done alternately. Always make a fresh silicon solution for getting the maximum results.

Research has shown that silicon provides maximum results if used regularly in the nutrition program compared to just a few applications throughout the season.

A large-scale, on-farm project is investigating silicon’s ability to improve heat and cold tolerance in citrus. Researchers are using two levels of silicon — 150 and 200 ppm — applied by foliar application and root drenching fortnightly (every two weeks) and monthly. So far, it is observed that 200 ppm of silicon applied fortnightly through foliar application is more beneficial in satsuma and red navel.

Recommendations for citrus growers using silicon include:

  • Use 150 to 200 ppm in monthly or fortnightly applications.
  • Choose a product with the maximum level of plant available silicon (at least more than 10%).
  • Continuous application of silicon throughout the season is recommended for optimal results.
  • Any type of sprayer can be used for silicon application; make sure to saturate all plant parts very well.

Source: UF/IFAS

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