Revitalizing the Earth: A New Perspective on Soil Health

Healthy soils are characterized by optimal biological, chemical, and physical conditions, which enable high crop yields. In such conditions, roots can proliferate easily, ample water infiltrates and is retained in the soil, the plant has an adequate nutrient supply, there are no detrimental chemicals in the soil, and beneficial organisms are highly active and capable of keeping potentially harmful ones in check, as well as stimulating plant growth.

The various properties of a soil are often interconnected, and these relationships should be taken into account. For instance, when soil is compacted, there is a loss of large pore spaces, making it challenging or even impossible for some of the larger soil organisms to move or survive. Moreover, compaction may cause the soil to become waterlogged, leading to chemical changes such as when nitrate (NO3–) is denitrified and lost to the atmosphere as nitrogen gas (N2). When soils contain a high amount of sodium, which is common in arid and semiarid climates, aggregates may disintegrate and cause the soils to have few pore spaces for air exchange. Plants will grow poorly in a soil that has degraded tilth, even if it contains an optimal amount of nutrients. Therefore, to prevent problems and develop a soil habitat that is optimal for plants, we can’t just focus on one aspect of soil but must approach crop and soil management from a comprehensive perspective.

Before delving into the key ecological principles and approaches to soil management, let’s first appreciate the remarkable abilities of plants. They employ a variety of systems to defend themselves from attack by insects and diseases. Sometimes they can simply outgrow a minor pest problem by putting out new root or shoot growth. Many plants also produce chemicals that slow down insect feeding. While not killing the insect, it at least limits the damage. Beneficial organisms that attack and kill insect pests need a variety of sources of nutrition, usually obtained from flowering plants in and around the field. However, when fed upon—for example, by caterpillars— many plants produce a sticky sweet substance from the wounds, called “extra-floral nectar,” which provides some attraction and food for beneficial organisms. Plants under attack by insects also produce airborne (volatile) chemicals that signal beneficial insects that the specific host it desires is on the plant. The beneficial insect, frequently a small wasp, then hones in on the chemical signal, finds the caterpillar, and lays its eggs inside it. As the eggs develop, they kill the caterpillar. As one indication of how sophisticated this system is, the wasp that lays its eggs in the tomato hornworm caterpillar injects a virus along with the eggs that deactivates the caterpillar’s immune system. Without the virus, the eggs would not be able to develop and the caterpillar would not die. There is also evidence that plants near those with feeding damage sense the chemicals released by the wounded leaves and start making chemicals to defend themselves even before they are attacked.

Leaves are not the only part of the plant that can send signals when under attack that recruit beneficial organisms. When under attack by the western corn root-worm—a major pest—the roots of some varieties of corn have been shown to release a chemical that attracts a nematode that infects and kills rootworm larvae. During the process of breeding corn in the U.S., this ability to signal the beneficial nematode has apparently been lost. However, it is present in wild relatives and in European corn varieties and is, therefore, available for reintroduction into U.S. corn varieties.

Plants also have defense systems to help protect them from a wide range of viral, fungal, and bacterial attacks. Plants frequently contain substances that inhibit a disease