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Phosphates vs Phosphites

This summary aims to clear up some confusion over products containing phosphorus.

phosphates vs phosphites 01The Facts

  • Phosphorus is an essential element for living cells, new growth can’t occur without it.
  • All phosphate fertilisers are derived from phosphoric acid.
  • Phosphite is derived from phosphorous acid. This has traditionally been used in fungicide applications against fungal like organisms i.e. downy mildew.
  • The truth: Plants can take up phosphite but cannot directly use it as a nutrient source.
  • Phosphites can be toxic at high rates

phosphates vs phosphites 02Background

  • Phosphite interest grew in the nineties with citrus and fruit crops.
  • However, past studies (on wheat and maize) have shown other crops to grow weakly when treated with phosphite.
  • Phosphite products are only registered as fertilisers to bypass expensive and time consuming pesticide registration procedures


  • What does it do? It is claimed that plants will excrete the phosphite through their roots; releasing locked up soil phosphate around the root hairs. This may benefit the poorer rooted crops.
  • Phosphites can not be used as a substitute for phosphate.
  • Our best advice would be to persevere with nitrogen little and often to promote new growth on backwards crops.

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