The soil, like air and water, plays a central role for life on Earth. It is the source of about 95% of our food and of many medicines. It also provides raw materials that we need for construction and clothing. Furthermore, the condition of the soil has a considerable effect on water quality.
The relatively new concept of soil security embraces that of soil health through soil sustainability. It encompasses food security, human health, governance and policy of land use and ownership, ecosystem services, biodiversity, climate sustainability, socio-economic aspects of life, and so on. It builds on broadly accepted security themes such as energy, food, and water security.
The soil has inherent properties, i.e. its capacity, such as particle-size distribution, mineral composition, and so on that affect the availability of trace elements, structure, and water-holding capacity. The current state of the soil is its condition with properties such as pH, organic matter, and nutrient content etc., that can be managed by agriculture.
To maintain health, humans depend on having an adequate supply of nutritious food, which in turn depends on the soil’s ability to provide food. Relations between the soil’s condition, the nutritional status of food, and human health are very complex and our understanding is still in its infancy. Our current knowledge comes from historical observations, animal health, and archaeology. However, with new and less expensive monitoring and analytical technologies, researchers increasingly gain insights into the relations between the soil, food, and the human body.
The microbiology of the soil and its diversity are major aspects of soil sustainability because of the many processes it is involved with. Some microbes compete with one another by secreting defensive chemicals to gain a competitive advantage in the soil ecosystem; these are antibiotics. Fungi and bacteria have been major sources of antibiotics, ~ 60% of those currently used. The soil is also a source of other medicines such as immunosuppressants and drugs for cancer treatment.
However, exogenous bacteria are now mixing with antibiotic-producing bacteria that occur naturally in soil. They exchange genetic material through horizontal gene transfer that can lead to the spread of antibiotic-resistant genes. Antibiotic resistance is a major problem, but with the suite of omics and qualitative and quantitative analytical methods, identifying potential antibiotics is now more feasible.
The human body requires 11 trace elements that come from the soil. Foods with small nutrient contents can have far-reaching consequences for human health; it is estimated that approximately two billion people suffer from undernutrition as a consequence of the poor low nutritional value of their food.
Trace elements can also be toxic, however, in the case of some, such as selenium, the difference between deficiency and toxicity has a narrow range. Four trace elements have major effects on human health: iodine, iron, selenium, and zinc. Iodine affects thyroid function as does selenium. Goitre and neurological problems can result when the soil and hence food contain insufficient levels of iodine.
Iron is probably the most frequent nutritional deficiency in the world with possibly two billion individuals suffering from iron deficiency anaemia. Iron oxides are plentiful, but their availability to plants in the soil is often poor and its eventual absorption from plants by humans is complex.
Almost all selenium in the body derives from food. Low levels of selenium are associated with cardiac problems and malignancy. Selenium is an important antioxidant in the body and occurs in 25 essential selenoproteins. Many of these are critical for catalytic and thyroid function.
Zinc deficiency is also widespread in the world. It is critical in the control of intestinal iron absorption. It binds with many proteins in the body and plays a vital role in gene expression and reproduction.
Most people have no idea about how the condition of the soil relates to their food and thus to their health. The public needs to know more and it is vital that soil scientists communicate more through education in schools and colleges. Another issue is to ensure that soil scientists engage with medical and other professionals about the importance of soil security and its role in human health. More open and broader training in such subjects will be the way forward together with advances in technology that provide the necessary information.
