The importance of mineral content and soil fertility in food nutrition

Story and Photography by Yvonne Lelong Bordelon

The nation that destroys its soil destroys itself. 
– Franklin D. Roosevelt, 1937

The old adage, “You are what you eat” is certainly true for humans, as well as plants. Recent research has shown that fruits and vegetables grown today contain fewer vitamins and minerals than those grown 50 years ago. It appears that the major cause of this decline is soil depletion as a result of modern intensive agricultural methods that have stripped many nutrients from the soil. 

Worm casting compost containing crushed eggshells, which are rich in calcium, can be applied to the soil for great results.

A landmark study conducted by Donald Davis and researchers from the University of Texas Department of Chemistry and Biochemistry compared the vitamin and mineral content of food crops grown today to those of crops grown decades ago and found that if more crops are grown in a given space it almost always results in lower nutrient levels in the produce. The median levels of minerals, vitamins, and protein in the fruits and vegetables also decline. Additionally, while the new types of crops do provide greater yields, greater pest resistance, and climate adaptability, their ability to manufacture or incorporate nutrients does not keep pace with their rapid growth.

In fall, sheet compost (layers of organic matter composed of manure, soil, compost, dead leaves, and ground oyster shells) can be applied to an existing bed or a new area.

It is well known that the fertility of soil used over and over to grow the same crop will become depleted and future crops grown in that soil will have reduced nutritional content. Experts also agree soil will contain fewer nutrients after it has been leached of minerals and necessary microorganisms by poor management or overuse of synthetic fertilizers, pesticides, and herbicides. If using any of these products, apply no more than recommended by soil test results.

By using a small moveable coop that can be repositioned around the garden, poultry can eat insect pests and work and fertilize different beds without having access to the entire garden.

Feed the Living Soil to Feed the Plant
The relationship between animals, plants, and the living soil is a mutually beneficial cycle – animal byproducts (such as manure) and plant material (organic matter) are added to the soil and broken down by microorganisms (such as bacteria and fungi), which process and excrete water-soluble nutrients that plants can use. The plants, in turn, provide food for the animals. 

A keyhole garden incorporates deep-layered raised beds with a central, permanent compost bin, which is never turned or removed. Water is applied through the bin to distribute the “compost tea.”

One of the first steps you can take to increase soil fertility is to have your soil tested to determine its actual deficiencies. While you are waiting for the results, you can improve the soil by using organic growing methods such as adding organic matter, in liquid or solid forms; growing nitrogen-fixing legumes; and adding minerals such as ground oyster shells. Rotating crops in the garden and minimizing the use of synthetic pesticides and herbicides will also increase microbe numbers.

Nitrogen-fixing snap beans are a good choice for the first year’s planting in a new sheet-composted garden.

Another important step is to keep the soil covered with plants or with a green cover crop or brown organic mulch during the off-season. This practice, especially in winter, will help minimize nutrient leaching and the loss of topsoil due to erosion. Both brown and green materials will also add nutrients when worked into the soil in early spring.

Beneath the ground is a massive network of fungi, which helps break down organic matter into water-soluble nutrients that plants use. Synthetic fertilizers, pesticides, and herbicides disrupt the soil food web by either killing off microorganisms or by disrupting the symbiotic relationship between plants and these microbes.

Composting plant materials and manure is another good way to improve soil fertility. Sheet composting, one of the less labor-intensive methods, is an excellent way to establish new beds or to enrich old ones during the off-season. Start with a layer of cardboard to smother the grass and weeds, and then layer organic matter on top. Good choices include coffee grounds, crushed eggshells, kitchen scraps, manure, grass clippings, wood ash, and crushed oyster shells. For most crops, start three to four months before planting.

The nitrogen-fixing legume, white Dutch clover (Trifolium repens) is an excellent cover crop and one of the best nectar sources for honeybees.

Bin composting and pile composting are both tried-and true-methods, but with these approaches you must move the material twice and turn it often. One raised bed design, known as a keyhole garden, combines a permanent compost bin with deep layers of branches, paper, cardboard, and other sheet composting ingredients. Vermicomposting with earthworms is another good option, one that will produce rich worm castings. 

Using animals, such as chickens and ducks, to till and enrich the soil and eat weeds and insect pests is an age-old practice that is still used today. The birds benefit from the healthy diet and produce eggs rich in protein and vitamins. 

If you don’t want to keep poultry, you can add alfalfa meal, blood meal, cottonseed meal, fishmeal, soybean meal, or greensand to the soil in amounts recommended by a soil test. As the fertility of the soil improves, the health of the fruits and vegetables will improve, which can result in increased disease and pest resistance and produce with higher levels of vitamins and minerals

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