We have, unfortunately, not been careful about the soil we live on and get our food and clothing from. We have for long exploited the land we live on. Even today shifting cultivation involves cultivating on a piece of land for a period of time and then moving on when the land loses its capacity to feed us. Most of the nations today are dealing with severe problems of soil depletion and have become dependent on artificial fertilizers. With fall in the nutrient content of the soil, there is reduced nutritional value and crop yield.
 Soil Depletion Causes
Soil depletion is caused by the combined effects of growing population densities, large-scale industrial logging, slash and burn agriculture and ranching. Other causes of depletion are over-tillage and overuse of inputs such as synthetic fertilizers and herbicides, which leave residues and buildups that inhibit micro-organisms.
Though it is a worldwide problem, soil erosion has received little attention in terms of research or discussion. In many respects, it appears that soil conservation has been a neglected subject in agricultural economics during the last two or three decades.
Animals and crops are no longer raised together in modern industrial farms. Livestock are raised on enormous CAFOs (concentrated animal feeding operations), and crops are mass-produced on separate farms. The manure generated in livestock farming is not used as fertilizer for crops as they are too expensive to transport. Instead, today's synthetic chemical fertilizers are used to support high-intensity mono-crop systems. It is estimated that only about half of all fertilizers are actually absorbed by plants; the remaining chemicals pollute the atmosphere, soils, and waterways.
 How Soil Depletion Affects Us
Once the soil is depleted of the basic minerals it produces less nutritional crop. The current yield of fruits and vegetables and grains, which are being raised on millions of acres of land, no longer contains enough of certain needed minerals. Vitamins without minerals are useless to the human body. When we consume food devoid of minerals we are prone to different types of diseases and disorders. Refer to Medical Dictionary of Conditions & Ailments  .Minerals help to structure our bone, tissue and body fluids. If these minerals are lacking in our food you need to supplement them. Visit Vitamins, Vitamin Supplements 
 Necessary Nutrients in Soil
Mineral nutrients which stand the risk of depletion are divided into three main categories:
• Beneficial elements
All three are necessary for a healthy, nutrient-rich plant. Each mineral nutrient is briefly discussed below. If you are interested in growing fruits and vegetables in your own garden you may refer to Organic Landscaping
• Air and water supply carbon, hydrogen and oxygen which combine to make up the backbone of all bio-molecules. Six other macro-elements such as nitrogen, phosphorus, potassium, calcium, magnesium and sulfur are found in soils
• Plants require nitrogen to make amino acid, proteins, enzymes and the light capturing molecule, chlorophyll. Before plants can use nitrogen, it must be converted from atmospheric N2 gas to available forms. Lightening and soil bacteria, either free-living or symbiotic in plant roots, can do this in natural systems. Nitrogen that is made available by any of these processes must be captured by plants and converted to biomass; otherwise it is lost by leaching or by conversion back to atmospheric nitrogen (N2)
• Phosphorus is a component of DNA and RNA. It is essential for all living cells and is required for energy transfer and use within plant and animal cells. Soil minerals such as apatite are sources of phosphorus.
• Potassium helps move sugars and carbohydrates within plants, which makes plant adjustments to drought conditions possible. Feldspars and micas are examples of soil minerals containing potassium.
• Calcium is required for plant cell walls and root growth. Feldspars, calcite and gypsum are calcium containing soil minerals.
• Magnesium is the central element in the chlorophyll molecule, and is involved in the activation and inhibition of enzymes. Biotite, olivene and vermiculite are magnesium sources in soils.
• Sulfur is required for plant synthesis of sulfur containing amino acids. Mineral sources of sulfur include gypsum and epsomite. Soil organic matter is also a substantial reservoir of sulfur. Maintaining soil organic matter levels is thus important to maintaining the sulfur supplying power of soils.
Micro-elements are equally important to the plant's life cycle, although required in lesser amounts. Micro-elements are generally needed from 0.05 to 100 ppm in dry plant tissue.
• Metal micronutrients are Iron, Manganese, Zinc and Copper. They are responsible for the extraction of energy from high energy bio-molecules like sugars and starches (electron transport chain). They are also heavily involved in the regulation of enzymes that mediate cellular biosynthesis and metabolism. Soil minerals include pyrite, limonite and olivine (iron); manganite, pyrolusite and rhodonite (manganese); franklenite, smithsonite and willemite (zinc); Chalcopyrite, chalcocite, and bornite (copper).
• Boron is present in some shales and in mineral tourmaline. Organic matter is also a large potential source of plant-available boron in soils. Boron is involved in the development and growth of new cells (meristems).
• Molybdenum is needed for enzymes that convert nitrogen into other forms needed for plant utilization; and is needed by for nitrogen fixation by rhizobium bacteria in the roots of legumes. It exists in very small amounts in various soil minerals.
• Chlorine is used by plants to help balance cation/anion charges in plants, to help plants adjust to water stress (osmotic adjustment), and in the photosynthesis process (photosystem II). Soil minerals that contain chlorine include halite and MgCl2.
• Nickel is involved in nitrogen metabolism, and is essential for plants supplied with nitrogen in the form of urea.
• There stresses. They have not yet been classified as necessary for all plants to complete their life cycle.
• Cobalt is essential for microorganisms that fix atmospheric nitrogen into plant-available forms. Granites and other acidic rocks are sources of cobalt.
• Increases in plant growth attributable to Vanadium have been reported for asparagus, rice, barley, lettuce and corn.
• Sodium can partially substitute for potassium in plants, when potassium is limiting, and helps plants, like sugar beets, resist drought stress.
• Silicon contributes to the structure of cell walls, strengthening tissues, reduces water loss and helps regulate some enzyme activities.
 What We Stand to Gain from Minerals
• Due to soil depletion we are not getting the minerals from our food like we did 50-100 years ago.
• Vitamins without the support of minerals are unable to carry out the biochemical activities of the body without minerals. All nutrients such as vitamins, proteins, enzymes, amino acids, carbohydrates, fats, sugars, oils, etc, require minerals for activity.
• All bodily processes depend on the action and interaction of minerals.
• There needs to be an adequate supply of minerals to the body to help maintain its balance between internal and external pressures (called osmotic equilibrium) of the body cells. This is important for normal functioning of the cells and for youthful health.
• Minerals, unlike vitamins, cannot be synthesized by living matter. This makes plant-derived minerals a more important supplement than vitamins
• Apart from working as catalysts to make enzyme functions possible, Minerals are also essential for antioxidant-enzyme function. Plant-derived minerals combined with enzymes make an alkaline detoxifying agent which neutralizes the acid metabolic byproducts of the cells and other toxic conditions within the body and prepares them for elimination.
• Hormonal secretions of the glands take place with mineral stimulation and the acid-alkaline balance (ph) of the tissue fluid is controlled by minerals.
• Just one mineral shortage can disturb the synergy and balance of the entire body. All other nutrients become useless or inefficient because of one mineral deficiency.
• As most fruits and vegetables today are grown with synthetic fertilizer, it is beneficial to supplement your everyday diet with minerals.
• Minerals are important both to the body and the bones and maintain the body's fluid balance. They are also parts of other important compounds, such as iron in blood, and iodine, which is a part of the thyroid hormone.
• The mineral content of the soil where the foods are grown determines the mineral content of certain foods
Organic Consumers Association  provides a number of useful information. Also see the Association’s webpage on clothing