Mineral nutrients in plants depend on what’s in soil


In a previous column we discussed vitamins. Today we will discuss another important factor in human nutrition — minerals.

The Earth is literally made of minerals. They are found in the foods we eat, and they perform many vital jobs in our bodies.

So let’s ask and answer a question:

Are all tomatoes or carrots or celery nutritionally the same?

The answer is no.

OK, why not?

Because soils in which they grow are not all the same. If a mineral is not in the soil or “growing solution,” it cannot be in the fruit or vegetable.

But that’s only half of the story.

Let me explain. Almost all plants require three basic minerals simply to grow: nitrogen, phosphorus and potassium. When a farmer grows a crop, those are the three basic ingredients in his fertilizer. Some farmers are now adding a few other minerals like magnesium, manganese and calcium.

But as far as trace minerals are concerned, the basic premise still stands: If the mineral is not in the soil in a soluble form, it will not be in the food growing in it.

Most soils do contain other trace minerals, but they may not be in a soluble form and hence will not be available to the plants. This is because of still another variable — the organic matter in the topsoil.

Organic matter in the soil is essential for the preservation and growth of soil microorganisms. It can be from decaying plants, manure or compost. The microorganisms are necessary for a very important job; they change insoluble rock minerals that plants cannot use into soluble minerals plants can absorb.

This is essentially where the term “organic” farming comes from. These soil bacteria, by the way, simply cannot stand many of the harsh chemical fertilizers being used in non-organic farming practices. It will kill them. Get some in your eye and you’ll understand.

It is the organic matter in the soil that retains moisture and sustains bacteria. Taking soil samples to determine mineral content of a field is good, but unless the test determines the solubility it will not tell us what we need to know: Is it available to the plants?

Another factor is that if a soluble mineral is in the soil, plant roots will probably absorb it even if it is not specifically needed for that plant to grow. Hence, minerals may be in the plant that might be needed for human nutrition.

As an example, let’s discuss the soils here in the Pacific Northwest.

Selenium is an essential mineral in both human and animal nutrition, but we have very little in our soils. Some soils may be totally devoid of the mineral. Ask any cattleman and he will tell you that without a trace mineral salt lick containing selenium their cattle may develop a condition called “wooden tongue” and will be unable to eat their food.

So let’s say a farmer in the region decides to go 100 percent organic. The food he grows may be totally organic, but by his using only homemade compost and manure from his own cows on his own selenium-deficient soil, no matter how “organic” he goes there may still be no selenium either in the compost or the manure unless he adds the mineral.

With this little background, let me ask you a question. How nutritious are hothouse vegetables?

First, they are grown in a non-soil medium, such as pebbles. The medium is flooded with a nutrient solution periodically to feed the plants through the roots. The basic minerals nitrogen, phosphorus and potassium must be in the solution, but it’s highly unlikely the solution will come near the number of minerals found in most soils.

Still any other mineral in the soil in soluble form will more than likely be absorbed by the plants’ roots and be in the food regardless of whether or not the plant needs it to grow. Some may be needed in human nutrition, some not.

So I challenge you to taste test two tomatoes. One grown “organically” and one grown with traditional commercial practices. I guarantee you will notice the difference in flavor, but the difference will be more than just the taste.

Retired chiropractic doctor Francis Trapani’s background includes 41 years of practice plus doing investigative reporting and fitness programs for broadcast media in Hawaii. He also received a bachelor of science degree in agronomy from Penn State University. For more information, go to drftrapani.com.


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