Healthy Soils

Healthy Soils 

It should come as no surprise that many cultures have considered soil central to their lives. After all, people were aware that the food they ate grew from the soil. Our ancestors who first practiced agriculture must have been amazed to see life reborn each year when seeds placed in the ground germinated and then grew to maturity. In the Hebrew Bible, the name given to the first man, Adam, is the masculine version of the word “earth” or “soil” (adama). The name for the first woman, Eve (or Hava in Hebrew), comes from the word for “living.” Soil and human life were considered to be intertwined. A particular reverence for the soil has been an important part of the cultures of many civilizations, including American Indian tribes. Although we focus on the critical role soils play in growing crops, it’s important to keep in mind that soils also serve other important purposes. Soils govern whether rainfall runs off the field or enters the soil and eventually helps recharge underground aquifers. When a soil is denuded of vegetation and starts to degrade, excessive runoff and flooding are more common. Soils also absorb, release, and transform many different chemi-cal compounds. For example, they help to purify wastes flowing from the septic system fields in your back yard. Soils also provide habitats for a diverse group of organ-isms, many of which are very important—such as those bacteria that produce antibiotics. Soil organic matter stores a huge amount of atmospheric carbon. Carbon, in the form of carbon dioxide, is a greenhouse gas associated with global warming. So by increasing soil organic matter, more carbon can be stored in soils, reducing the global warming potential. We also use soils as a foundation for roads, industry, and our communities. WHAT KIND OF SOIL DO YOU WANT? Soil consists of four important parts: mineral solids, water, air, and organic matter. Mineral solids are sand, silt, and clay and mainly consist of silicon, oxygen, alu-minum, potassium, calcium, and magnesium. The soil water, also called the soil solution, contains dissolved nutrients and is the main source of water for plants. Essential nutrients are made available to the roots of plants through the soil solution. The air in the soil, which is in contact with the air above ground, provides roots with oxygen and helps remove excess carbon dioxide from respiring root cells. When mineral and organic particles clump together, aggregates are formed. They create a soil that contains more spaces, or pores, for storing water and allowing gas exchange as oxygen enters for use by plant roots and soil organisms and the carbon dioxide (CO2) produced by organisms leaves the soil. Farmers sometimes use the term soil health to describe the condition of the soil. Scientists usually use the term soil quality, but both refer to the same idea— how good is the soil in its role of supporting the growth of high-yielding, high-quality, and healthy crops? How would you know a high-quality soil from a lower-quality soil? Most farmers and gardeners would say that they know one when they see one. Farmers can certainly tell you which of the soils on their farms are of low, medium, or high quality. They know high-quality soil because it generates higher yields with less effort. Less rainwater runs off, and fewer signs of erosion are seen on the better-quality soils. Less power is needed to operate machinery on a healthy soil than on poor, compacted soils. The first thing many might think of is that the soil should have a sufficient supply of nutrients throughout the growing season. But don’t forget, at the end of the season there shouldn’t be too much nitrogen and phos-phorus left in highly soluble forms or enriching the soil’s surface. Leaching and runoff of nutrients are most likely to occur after crops are harvested and before the follow-ing year’s crops are well established. We also want the soil to have good tilth so that plant roots can fully develop with the least amount of effort. A soil with good tilth is more spongy and less compact than one with poor tilth. A soil that has a favorable and stable soil structure also promotes rainfall infiltration and water storage for plants to use later. For good root growth and drainage, we want a soil with sufficient depth before a compact soil layer or bedrock is reached. We want a soil to be well drained, so it dries enough in the spring and during the following rains to permit timely field operations. Also, it’s essential that oxygen is able to reach the root zone to promote optimal root health—and that happens best in a soil without a drainage problem. (Keep in mind that these general characteristics do not hold for all crops. For example, flooded soils are desirable for cranberry and paddy rice production.) We want the soil to have low populations of plant disease and parasitic organisms so plants grow bet-ter. Certainly, there should also be low weed pressure, especially of aggressive and hard-to-control weeds. Most soil organisms are beneficial, and we certainly want high amounts of organisms that help plant growth, such as earthworms and many bacteria and fungi.