How many times have you read that we need to take various mineral supplements because our soils are depleted of minerals? I couldn’t tell you how many times I’ve read that we need magnesium because our soils are deficient. But magnesium is in every molecule of chlorophyll, and if there was no magnesium in the green parts of the plants they’d make no energy and die, so there must be magnesium there. It’s true you won’t see it if the plant has some other coloration, like purple lettuces for example, but if there’s no chlorophyll the plant won’t grow. Something like Romaine lettuce, though, the darker green it is, the more magnesium it has.
So I decided to try to find some source that tells me current and older magnesium levels. I couldn’t find it. Here are some notes I took, in hopes that someone else will find it interesting.
Magnesium is the 7th most abundant element in the Earth’s crust
and is a major rock forming element
Very common in clays.
Magnesium in soils is lost easier in acidic (low pH) soils than in basic soils.
Magnesium supplementation in fertilizers is emphasized on lots of sites, probably because of its role in chlorophyll.
Scientific American 2011
cites December 2004 paper in Journal of American College of Nutrition
A landmark study on the topic by Donald Davis and his team of researchers from the University of Texas (UT) at Austin’s Department of Chemistry and Biochemistry was published in December 2004 in the Journal of the American College of Nutrition. They studied U.S. Department of Agriculture nutritional data from both 1950 and 1999 for 43 different vegetables and fruits, finding “reliable declines” in the amount of protein, calcium, phosphorus, iron, riboflavin (vitamin B2) and vitamin C over the past half century. Davis and his colleagues chalk up this declining nutritional content to the preponderance of agricultural practices designed to improve traits (size, growth rate, pest resistance) other than nutrition.
Note that those “reliable declines” don’t include magnesium, and they’re attributed to breeding varieties of plants for growing big (ready to harvest) crops quickly, not the soil being deficient.
“Efforts to breed new varieties of crops that provide greater yield, pest resistance and climate adaptability have allowed crops to grow bigger and more rapidly,” reported Davis, “but their ability to manufacture or uptake nutrients has not kept pace with their rapid growth.” There have likely been declines in other nutrients, too, he said, such as magnesium, zinc and vitamins B-6 and E, but they were not studied in 1950 and more research is needed to find out how much less we are getting of these key vitamins and minerals.
As close as I got to showing the soils are low in Mg is that they thought it was possible but had no measurements to compare it to.