Trace Mineral Fertilizers – How Many Nutrients Do Plants Need?

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Robert Pavlis

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.

Soil Science for Gardeners book by Robert Pavlis
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.

Building Natural Ponds book, by Robert Pavlis

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

 

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Robert Pavlis

I have been gardening my whole life and have a science background. 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!

37 thoughts on “Trace Mineral Fertilizers – How Many Nutrients Do Plants Need?”

  1. would you happen to have a recommendation for meeting those 24 useful minerals that could be found and applied in the same manner as rock dusts?

    i’m looking for the most convenient and cost effective possible, as my situation and scale of farming highly demands it.

    Reply
  2. Hi,

    I am quite new to gardening but reading your articles have been very eye opening.
    Referring to the comments above, you stated that there is no science on plant available nutrients of Azomite. I was wondering whether the cation exchange capacity would show this?
    Is there an actual product test that could determine how plant available nutrients really are, otherwise how would we know which products work?

    Thanks in advance.

    Reply
    • “you stated that there is no science on plant available nutrients of Azomite” – I never said that.
      “wondering whether the cation exchange capacity would show this?” – CEC of what? What should it show?
      If you take azomite and put it in some water, plant available nutrients will dissolve in the water, just as they would in soil. you can then test the water.

      Reply
    • “Liebig’s Law of the Minimum states that the local yield of terrestrial plants should be limited by the nutrient that is present in the environment in the least quantity relative to its demands for plant growth, and this statement has been confirmed worldwide.”

      I don’t disagree with that. What has that got to do with the type of nutrients that plants need?

      You have not pointed out a single thing I said that goes against this law. Maybe you need to review Liebig’s Law.

      Reply
  3. I think a lot of people buy things like Azomite for the same reason as they buy a Multivitamin: it’s an insurance policy. True, I have no idea whether my soil is short on some micronutrient, but given the low cost of application and no harm, why the heck not….

    Reply
    • They might buy for that reason – but they made a poor choice. A multivitamin actually contains vitamins that are released to the body and if required, would add some benefit. In the case of azomite – there seems to be no evidence that the benefits are released to soil in any short term horizon.

      adding soluble fertilizer would be more like taking a multivitamin – in case you need it.

      Reply
    • That could be the case. However, there is good reason to use a product like Azomite. First, let me say that the first vitamin pills contained 5 nutrients. The first garden fertilizer I know of contained 3 nutrients. We had humble beginnings. Now, if you look at the elements that are required to sustain healthy life for animals and plants, while they differ in quantity, and sometimes in form, they follow roughly the same prioritizations. And, each is approaching numbers that include all natural elements. I do not find it odd that the elements that plants extract from soil are also needed by animals. And, this gets to the point. Look at the nutritional breakdown that vegetables supply to animals. Where did the elements originate? The soil. The plants took up these elements. Animals then eat some of these plants. What happens to those elements in the garden soil over time? If you get periodic soil test, you will start to see where those elements are going. They are not being returned to the soil as plants drop leaves, die, and decompose. We are taking those elements to the kitchen table. We consume them. We return them to rivers, lakes, and oceans.

      A second important point is our use of nitrogen. If you grown corn, you understand how much nitrogen plants can require. The functional definitions for approximately half of the elements plants require aids in nitrogen fixation, nitrogen uptake, or other portions of the nitrogen cycle. Cobalt is important for nitrogen fixation. Amazingly, you can find reports that the plant requirements for cobalt are not understood. At the same time, we see that nitrogen is applied in such great quantities, runoff is causing eutrophication. As well, when a fertilizer blend is used, other elements runoff and cause other issues. We appear to be ignoring the importance of cobalt and other elements that will allow us to use less nitrogen and get the same results. Interesting that there is big money in nitrogen, but not in very small doses of cobalt.

      It concerns me greatly that physicians are prescribing mineral supplements. Calcium supplements are one of the common ones. If you have adequate calcium in your soil and you grow and eat the right vegetables, you will improve your health. Your body will take up some of the calcium in things like greens and beans. If you buy produce, you will likely get plants that are lacking in proper levels of elements. If you buy over the counter mined calcium, it will pass right through you and back to the ocean.

      Get a soil test. If you see a deficiency, Azomite is the most complete mineral additives I know of. Apply it. Get another soil test in a year. Repeat. BTW – I use Azomite but have no affiliation with the company or product.

      Reply
        • As we know, there is no science that shows much of anything regarding trace elements that benefit plants or animals. There simply is no great profit in it. The profit is with the nitrogen, iron, B vitamins, Vitamin C, etc. That is where you see the science at work.

          I want to challenge everyone to look at anecdotal evidence and report your findings. It will require 9 pots or grow bags, 9 seeds, potting mix, a little clay, and a little Azomite.

          Just put the soil less mix in the 9 pots. Separate them into 3 groups. Make note of the fertilizer the manufacturer added to the mix. Plant the 9 seeds. Take 3 pots designated as the second group and sprinkle fine clay on the top. Take another 3 pots of the third group and sprinkle Azomite on top. Provide the same water, sun, and fresh air to all 9.

          Initially, growth and apparent health should be very similar. As the stresses of summer work on the plants, you should see some differences. The first group has a growing medium with nitrogen, phosphorous, and potassium. The second group has that plus the soil elements that are held in the clay. The third group has the Azomite added to the mix. If soil releases elements to plants, the second group with the clay should be healthier plants and produce better fruit than the first control group. If the third group looks like the first group, then, you will have anecdotal evidence that Azomite does not release adequate mineral elements to aid in plant growth, health, and good fruit production.

          Make note of the appearance of all 9 plants. Is there a difference? Taste the fruits. Is there a difference? I will probably used tomatoes for this test. Use whatever you like.

          Reply
          • “there is no science that shows much of anything regarding trace elements that benefit plants or animals” – that is simply not true. We certainly know which trace elements are needed and not needed by plants.

  4. Humans need small amounts of selenium in their diet to create the amino acid selenocystine. They have to get this from their diet, which means that either the plants they eat or the plants meat animals eat have to have it. If you don’t get enough selenium your body is making abnormal cells, which is the definition of cancer. That’s why I use liquid seaweed and Sea 90 in my hydroponic systems.

    Reply
  5. First off I would like to point out that why yes there is no evidence that all of the elements are used let’s remember that some plants grow deep tap roots and bring all sorts of minerals and nutrients to the surface. The deep tap roots do essentially break up rocks of all types and that is what this bag is; Powdered rock. So to cast this aside as a snake oil is foolish and arrogant of man. However fellow gardeners we must remember other things like vitamins also help our plants. There is no one size fits all. Our soil is alive and the best we can do is respect that. And give it all we can to help.

    Reply

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