Sodium, cobalt, vanadium, and silicon are essential micronutrients for some plants. Selenium, an essential micronutrient for humans that is toxic at high intakes, is not considered an essential nutrient for plants and not used as a fertilizer. In any case, humans need to ingest only very small amounts of this element. In the United States selenium deficiency appears nonexistent. Soil nutrient losses are a natural consequence of plant growth, which is indispensable to human life.
Plants stabilize soils and oxygenate the atmosphere.
Humans derive essential nutrients both from plants and from animals that derive these nutrients from plants. The arrows in the diagram illustrate the paths that K may take as it moves from one form to another. Although such compounds constitute the single largest potassium reservoir in soils, they give up the mineral only very slowly. Fixed K is unavailable to plants. Exchangeable K is held loosely by clay minerals and can go into the soil solution, where it becomes available to plants and microorganisms.