The macronutrients of plants are carbon, hydrogen, oxygen, nitrogen, potassium, calcium, phosphorus, magnesium, and sulfur. These all are nearly or in some cases far greater than one percent of the dry weight of a plant. The micronutrients are iron, chlorine, copper, manganese, zinc, molybdenum, and boron. Each of the micronutrients constitutes less than one to several hundred parts per million in plants. Sodium, silicon, cobalt, and selenium are beneficial elements. Research has not shown that these elements are essential for plant growth and development.