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Does an apple a day really keep the doctor away? Not anymore, according to soil health experts—unless the apple comes from a tree grown in healthy, organic soil.

According to Australian soil scientist Christine Jones, as reported by Courtney White in his book, Grass, Soil, Hope, apples have lost 80 percent of their vitamin C.

And that orange you just ate to help ward off a cold? It’s entirely possible that it contains no vitamin C at all.

A study looking at vegetables from 1930 to 1980, found that iron levels had decreased by 22 percent, and calcium content by 19 percent.  In the United Kingdom, from 1940 to 1990, copper content in vegetables fell by 76 percent, and calcium by 46 percent. The mineral content in meat was also significantly reduced.

Food forms the building blocks of our bodies and health. Soil forms the basis for healthy food. Unhealthy soil grows poor quality food. And poor quality food means poor health.

Even our mental health is linked to healthy soil, rich in microbes.

So what’s happened to our soil? It’s been under assault since the advent of modern industrial agriculture, with its monocrops, fertilizers, pesticides and insecticides.

The term “biodiversity” evokes images of a rich variety of plants—trees, flowers, grasses, fruits, vegetables—mixed in with an equally diverse collection of animals, insects and wildlife, all co-existing in a lush environment.

But there’s a whole world of biodiversity that lives beneath the surface of the earth—at least in areas where the soil hasn’t been destroyed. And that biodiversity is essential for the growth of nutrient-rich foods.

The Earth’s soil is a dynamic mixture of rock particles, water, gases, and microorganisms. Just one cup of soil contains more microorganisms than there are people on the planet. These diverse microbes compose a “soil food web,” a complex chain beginning with organic residues like decaying plant and animal matter, and ranging from bacteria and fungi to nematodes (worms) and bugs. Just by going about their daily lives in the dirt, these organisms decompose organic matter, stabilize the soil and help convert nutrients from one chemical form to another.

This rich diversity of microbes affects most soil properties, including moisture content, structure, density, and nutrient composition. When microbes are lost, the properties of soil that allow it to stabilize plants, convert chemicals, and perform other vital functions are also reduced.  The microbe content of soil—its biodiversity—is nearly synonymous with soil health and fertility.

As Daphne Millier, physician, author and professor, writes, “soil teeming with a wide diversity of life (especially bacteria, fungi, and nematodes) is more likely to produce nutrient-dense food. Of course, this makes sense when you understand that it is the cooperation between bacteria, fungi, and plants’ roots (collectively referred to as the rhizosphere) that is responsible for transferring carbon and nutrients from the soil to the plant—and eventually to our plates.”

Unfortunately, human interactions have negatively impacted almost all aspects of soil health—we are responsible for the degradation of more than 40 percent of worldwide agricultural land.  

What have we done to the soil? For starters, we’ve destabilized our soil ecosystems through the widespread and reckless use of chemicals—herbicides, pesticides and fertilizers—that destroy nearly everything in sight, except the plants themselves (many of them genetically engineered to withstand herbicides and pesticides). We end up with corn, soy, alfalfa and other crops that may appear “healthy,” but in truth, are nutrient-deficient because the nutrient-cycling quality of the soil has been destroyed.

And we do it as a matter of routine, even though it’s estimated that in the case of pesticides, for instance, only 0.1 percent of pesticides used actually interact with their targets; the rest pollute plants and soil.

As any gardener knows, nitrogen is one of the three essential soil nutrients. (Potassium and phosphorous are the other two). In order for nitrogen to “feed” plants, it must first be converted to ammonium or nitrate. Soil microbes, which are critical to the nitrogen cycle, achieve this conversion by feeding on decaying plant matter, digesting the elemental nitrogen contained in the decayed matter, and excreting nitrogen ions. The newly available nitrogen is taken up by plants, where it becomes available to humans either directly (when you eat the plant) or indirectly (through consumption of grazing animals).

What happens when soil is stripped of the microbes required to complete the nitrogen cycle? Farmers often resort to fertilizers that contain nitrogen. But the over-use of fertilizers leads to nutrients (like nitrogen) building up beyond the capacity of soil microbes to convert it into usable, absorbable nutrients. Too much nitrogen actually kills plant life.

According to the Union of Concerned Scientists, factory farming, where thousands of animals are confined in small spaces and fed grains (supplemented with antibiotics and hormones), rather than the forage nature intended, is behind much of the damage humans have inflicted on the soil.

At the core of industrial food production is monoculture—the practice of growing single crops intensively on a very large scale. Corn, wheat, soybeans, cotton and rice are all commonly grown this way in the United States.

Monoculture farming relies heavily on chemical inputs such as synthetic fertilizers and pesticides.

In a monocropping system, what soil organisms aren’t destroyed by chemicals and over-tilling, are edged out when their plant symbionts are lost.

The impact of the loss of soil biodiversity is linked to the increase in asthma and allergies in western societies. The human immune system is developed early in life through exposure to environmental stimuli. When meat or vegetables are lacking in certain bacteria and microbes, children can’t formulate that early immune response and so may develop an allergic reaction later in life. 

If the numbers are any indicator, there’s a crisis in worldwide soil health that is rapidly becoming a crisis in human health. Converting from factory farms and conventional crops to pasture-grazing livestock and organic farming are the solution. According to one study, it’s possible to more than double soil biodiversity by replacing conventional farming methods with organic farming.

But we shouldn’t be satisfied with simply scaling back the problem. Regenerative agriculture is a crucial tool for actively reversing the harm caused by Big Ag practices. And there’s no time to waste—scientists say that a single square centimeter of soil can take from 20 to 1000 years to form.

Hannah Bewsey is a writer/researcher for the Organic Consumers Association.

Katherine Paul is associate director of the Organic Consumers Association.