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Trace Mineral Fertilizers – How Many Nutrients Do Plants Need?

I just replied to a comment in my Fish Fertilizer Post which said, “It’s surprising the article makes no mention of the full spectrum of minerals present in sea food, and therefore the fertilizer. Sea water is known to have an astounding 82 elements (don’t have the link, please Google it) The only thing that prevents us from using sea water as fertilizer is the high sodium content. Fish do the wonderful job of filtering out that excess sodium and leaving you with extremely mineral rich organic matter ! “.

A couple of weeks ago at the Guelph Organic Conference, one of the salespeople selling an Australian sea salt extract, claimed that his product contained 99 nutrients that plants need.

I found the following claim on a company website; “Azomite – Organic Trace Mineral Powder – 67 Essential Minerals for You and Your Garden”. Azomite is a brand name product made from “special” rock dust.

Why does fertilizer only show three nutrient numbers, NPK, when plants need either 67, 82 or 99 nutrients? Inquisitive gardeners want to know.

Periodic Table of Elements

Periodic Table of Elements

Nutrients vs Elements

You might have noticed that the comments above used different terms. One said elements and another said nutrients. “Element” is a specific chemical term that describes a single type of atom. Carbon is an element, and aluminum is an element. All known elements are listed on the Periodic Table (see above) which shows around 118. Of these 94 exist naturally and the rest are man-made in the lab and are very unstable.

The term nutrient has various meanings, but in terms of plant growth it usually refers to the elements, minerals, or simple compounds that plants use. In most cases these are elements or ions of elements, but a few like CO2 and water are simple compounds. Of course, a molecule of water (H2O) consists of just two elements, hydrogen and oxygen. For the benefit of this post the term nutrient will only refer to elemental nutrients and does not include a wide range of organic molecules that could also be called nutrients.

Regarding the statement “Sea water is known to have an astounding 82 elements (don’t have the link, please Google it)” – I did Google it. According to Standford University (ref 2) there are 42 elements or 47 minerals and metals in sea water.

Essential Plant Nutrients

The essential plant nutrients include carbon, oxygen and hydrogen which are absorbed from the air. The other essential nutrients, which are obtained from the soil, (or water in the case of water plants) include:

That is a total of 18. There is still debate as to whether silicon, nickel, chlorine and cobalt are essential.

What Nutrients Do Plants Use?

You might think we just answered this question, but plants can use additional nutrients which are non-essential. This means plants will use them if available, but they do not need them in their diet. Some of these nutrients are only found in certain types of plants.

Non-essential nutrients, which are also called beneficial nutrients, include aluminum (Al), silicon (Si), selenium (Se), sodium (Na), vanadium (V) and gallium (Ga). (ref 1)

Silicon is used to strengthen cell walls, which makes plants more drought resistant.

Sodium replaces potassium in certain reactions, is used by C4 plants and helps control osmotic pressure.

Vanadium is used by green algae.

This brings the total of useful nutrients to 24.

Plants also absorb other elements like cadmium and lead. These may provide some benefit to the plant but current evidence suggests they don’t.

Benefit of More Elements

There are 94 natural elements and plants use 24 of these. What is the benefit of the remaining 70 to plants? Nothing.

The myth that plants benefit from more nutrients is a consequence of marketing, based on peoples belief that “more is better”. If some nutrients are good for plants, other nutrients might also be important. This is not the case.

Most garden soil contains plenty of the micro-nutrients. Unless a soil test says differently, assume your soil has enough of these. Buying extra nutrients that plants don’t need is a waste of money and resources.

References:

  1. Forms of nutrients in soil and their functions in plants; http://eagri.tnau.ac.in/eagri50/SSAC122/lec05.pdf
  2. Over 40 Minerals and Metals Contained in Seawater; http://www.miningweekly.com/article/over-40-minerals-and-metals-contained-in-seawater-their-extraction-likely-to-increase-in-the-future-2016-04-01/rep_id:3650

 

Robert Pavlis
Editor of GardenMyths.com
I live in southern Ontario, Canada, zone 5 and have been gardening a long time. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

I hope you find Garden Myths an educational site that helps you understand your garden better.

21 Responses to 'Trace Mineral Fertilizers – How Many Nutrients Do Plants Need?'

  1. Valdas says:

    “Healthy” plant is not enough. We must think what human cell need to be healthy as plant is the source of nutrients for us. Life is more biophysics not biochemistry. Not all humic extracts are made with pH 13 and some are very bioactive and beneficial for plants especially in unhealthy industrial soils.

  2. AB says:

    Great Website, thank you for the work you do. Useful and enjoyable information. I would be interested to hear your thoughts and reactions to the work of Dr. Maynard Murray. If you can, grab a copy of his Sea Energy Agriculture book that documents his agricultural experiments using trace minerals.

    • I have not looked at his work.

      • tolga erok says:

        and the finding are??? to be honest i did use a very small amount of sea water collected at the local beach and made a weak solution of it and watered 6 zucchinis with it and the other 6 with normal tap water. both experiments had exactly the same soil mixture.

        the 6 watered in sea water did show much better growth in vigor and yielded a little more and were more resistant to mildew powder .

        would i do it again….no….why…..not much difference between the yields and the extra effort wasnt worth it…..

  3. Rena Clark says:

    Very timely article for me. We have failed in our quest to plant privacy trees twice last year. It seems the only ones to have survived out of 86 were the few that were not evergreens and were at least 4 feet tall. We suspect our soil, overwhelming clay, is the reason. This article is helpful in my quest to determine what needs to be done before we spend additional money on trees. Any suggestions of evergreen trees for privacy that do well in small backyards in Knoxville TN are most welcome. We tried Giant Thuja and camellias.

  4. NOOB says:

    Silica was only recognized as a micronutrient in 2012 in the USA. Japan has been showing results with it since the 1950’s. Probably cause rice type plants have way more silica uptake than plants like wheat and corn. The point is some plants need some elements more than other plants do.

    And silica is a very interesting case in that it is shown in literature to improve plant immune response and disease resistance. Some plants can grow fine without it, generally, and others have better pest resistance with it. Still other plants, it is as important as a macro nutrient, like rice.

    The science on elements does not seem to be settled. There are some elements that are well understood. Others have not been studied enough or studies repeated enough to give confidence in the results.

    One might think that such an old feild like agriculture has all its science settled. Dont be fooled! Much work is to be done. Challenging old science and discovering better truths. And the complexity of the questions we would like answered are increasing quickly. Remember the humic and fulvic acid sillyness? Still humic and fulvic gets results…

    But the last thing we need is myths in our gardening. We need more science for our plants!

  5. Shreesh Ponkshe says:

    You seem to be publishing comments selectively.

    • Correct. If a comment is not related to the topic, or it does not make any sense, or it uses abusive language, or it calls me names – it gets deleted. Others are not deleted.

  6. Nadav Ziv says:

    Dear Robert,
    I’m a big fan of this blog, enjoy and learn every time I visit. Your ability to explain complex gardening sci stuff in simple terms is a real gift. I couldn’t find your email so I’m trying here, hope it’s OK…
    I want to translate some of your posts mainly concerning compost and composting to Hebrew and use it on my personal blog. I wouldn’t do it without your permission and of course crediting your work/posts in every publication. I would appreciate your agreement but will accept your disagreement as well.
    Thanks,
    Nadav.

  7. You’re the best! So do you agree that the better synthetic and organic fertilizers that provide N-P-K plus the micronutrients (usually the nine you list) are good, sound horticultural products?

    • How is “good, sound horticultural products” defined? I agree that such products will provide the nutrients your plants need, both in pots and in the garden. The micronutrients are probably not needed in the garden so using and manufacturing such products are not environmentally sound. How good they are also depends on how they are sourced and manufactured. for example bat guano is a good source on nitrogen, but has a terrible impact on bat habitats.

  8. Jim says:

    While subscribing to the premise that plants do not need nor use the full spectrum of elements, I question whether some elements beyond the 24 useful nutrients for plants may be needed or use by various organisms in the broader soil food web and thus needed for heathy soil. Are there data to address my question.

    • That is a valid question. The answer is probably no. Most living organisms have similar biochemical processes when we look at them at a high level. They all make DNA and protein, for example. The chemical structure of these molecules is similar. In order for an organism to benefit from other elements it would need different chemical reactions than other organisms. I am sure there are some such special organisms in unique environments, but most organisms in soil would not fall into this category.

  9. janet says:

    My intuition tell me that adding all the elements in salt water is beyond what is needed by plants in nature. However, most of this element testing is not done by the scientific community because it doesn’t support real product needs. It remains somewhat of a mystery how many elements are needed for plant growth and if they can be supplied by natural soil. Your writing is wonderful and thought provoking. Please let me know if I can help proof read sentences such as ” Silicon is used to strength cell wall”. Details count in the credibility battle.

    • Re: ” It remains somewhat of a mystery how many elements are needed for plant growth” – not really since it is fairly easy to makeg a mixture of elements, and if plants grow they don’t need elements not included. Testing minor benefits of non-essential ones is a bit more difficult.

      Thanks for the correction.

    • Top half of your comment – well said.

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