Mineral Depletion in Soil

Patricia Zifferblatt | June 24, 2009


Minerals and trace elements are an integral part of the chemical structure of almost all vitamins, enzymes, amino acids and a host of other substances that our body depends upon to be healthy and function properly. Did you know that plants absorb around 70 to 80 different minerals from the soil during the time they are growing? The majority of fertilizers used today by commercial growers contain only about five or six types of minerals. So where will the rest of the minerals come from? Is it possible to use up all the nutrients in the soil and eventually run out? What can we do to make a difference?

It will help us to know what minerals are and where they come from in the first place. Textbooks tell us: A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition, a highly ordered atomic structure and specific physical properties. This definition gives us some important information that can help to answer the questions we’ve asked. First, our soil is made up of minerals of all kinds. Thousands of years ago the soil was richly laden with minerals, the result of millions of years of shifting earth (which created pulverized rock), decaying plant life and animal waste products. These same geological processes happen today, but because we mass-produce so many crops now, there is a danger of depleting the soil of some minerals that natural processes can’t replace fast enough.

It has been estimated that although mineral depletion has been underway for thousands of years, about 70% of it has occurred over the last 100 years alone. And it appears that this is happening worldwide, with North America leading the pack at an 85% depletion level. Over the years many farmers engaged in practices that helped prevent mineral depletion. Crop rotation was one such practice whereby the grower changed what was grown on a particular section of land from year to year. For example, this could mean that one year the field was planted in corn and the next year it would be hay. Since different crops require different ratios of micronutrients, this practice slowed down the depletion rate of any given mineral. Many farmers in the past also allowed a section of their land to lie ‘fallow’ for a year so that no minerals would be taken out of the soil for that year. They did this by systematically choosing a different section of land each year to let it “rest”. So, if we have been using these responsible farming practices all along, why is depletion occurring?

According to agricultural expert Mick Bridge, the reason for mineral depletion is very complicated. Bridge says that ‘good’ soils contain a reservoir of micronutrients (minerals) in excess of what the plant needs to grow. Not all soil contains the same ratio of minerals, nor is that ratio a fixed amount. (Remember, soil is basically weathered rock whose particles continuously break down into smaller particles as a result of rain and temperature extremes.) Other factors such as the water solubility of the available mineral and the pH (acidity level) of the soil also contribute to how many minerals are actually available to the plant at any given time. The most efficient method for animals and humans of getting mineral needs met is by eating plants. A plant requires the mineral to be in its smallest molecular form so that it can be taken into the plant attached to a water molecule. This will ‘feed’ the plant which, in turn, can feed us. The most fertile soils tend to be those where a combination of pulverized rock and decaying animal and vegetable matter are fed by rivers and/or mountain washes to produce high levels of humus and mineral-rich soils. Under these conditions, the replenishment of minerals to the soil can even exceed the amount taken up by plants, leaving the soil rich in mineral content.

Bridge points out that all soil receives a continual input from external sources, whether in the form of rainfall, irrigation, or flooding. Also, all soils receive nutrients, either from chemical/mineral sources (commercial fertilizers) or from a more ‘natural/organic’ source (compost). He writes that crops fail, not because of a shortage of just one mineral, but because the soil cannot cope if one crop is continuously grown in the same soil year after year. This agricultural practice drains the soil of certain minerals while leaving the rest behind. Even if fertilizer is used, an especially large crop yield can deplete the soil of available micronutrients faster than they can be replaced. In today’s race to produce high crop yields to meet the demands of local and export markets, the soil doesn’t have time to replenish its mineral content before the next crop is sown.

Another issue is erosion. Flatlands are especially vulnerable to wind and flood erosion if care is not taken to stabilize the soil with some form of winter growth. We learned that lesson the hard way during the ‘Dust Bowl’ years when topsoil was literally blown out of many of our breadbasket states. That’s why today you will see many fields planted in winter wheat or a grass of some kind after harvest. These plants will hold the soil in place and return the micronutrients to the soil when the farmer plows the plants under the following Spring.

The news that mineral depletion has now become as issue for the consumer shouldn’t come as a total surprise. Any condition that results in low levels of plant nutrients means that the consumer will not get the amount of nutrition assumed to be there even when eating a healthy array of fruits, vegetable and grains. This suggests that we need a long-term plan as well as a short-term solution to address the problem head-on.

Long-term Plan Agriculture will need to look at ways to meet the consumers’ needs while protecting the land from mineral depletion. For example, researchers have found that sulfur-deprived grain has nearly 30 times more amino acids than other grain. But, surprisingly, when flour made from that grain is heated above a certain temperature, a neurotoxin/carcinogen is produced at a level almost eight times higher than what is considered normal. As a result of this discovery, hundreds of studies are currently underway to look at the impact of mineral depletion in the foods we eat, with particular attention given to studies of specific kinds of minerals. Research focused on finding more eco-friendly fertilizers must also continue. Some bacteria play a vital role in converting soil minerals into chemical forms that plants can use. Just as some types of fertilizer in use today alter the pH balance to such an extent that ‘good’ bacteria cannot survive, many commercial pesticides and herbicides are having a similar effect on beneficial fungi in the soil. It may be a good idea to insure that growers engage in regular soil testing and be required to augment the soil with minerals, as needed, for the crops they intend to sell to the public.

Short-term Solution In the meantime, consumers can increase their intake homegrown fruits and vegetables. In the present economy, more and more people are trying their hand at gardening and turning to the local farmers market for produce. This may turn out to be healthy solution as well as an economical one for many of us. First-time gardeners are tilling soil that is probably richer in minerals than agricultural land that has been cultivated for years. While the crop yield will probably not be adequate to meet all nutritional needs for a family, it will certainly be a terrific addition to what must be purchased. And even though the mineral content of some foods we purchase may be a little low, don’t stop eating the fruits, vegetables and grains that are high in mineral content. A good multiple vitamin containing minerals can help boost those depleted levels as well.