An element is considered essential to plant growth if it becomes part of plant tissue or is involved in metabolic functions and the plant cannot complete its lifecycle without it. There are 17 elements currently considered essential to plant growth. Listed in order of abundance in plant tissue, the 17 essential elements are: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Potassium (K), Calcium (Ca), Magnesium (Mg), Phosphorus (P), Sulfur (S), Chlorine (Cl), Iron (Fe), Boron (B), Manganese (Mn), Zinc (Zn), Copper (Cu), Molybdenum (Mo), and Nickel (Ni). Plants obtain C, H, and O from air and water during photosynthesis. Together, these three elements make up approximately 95% of a plant's dry matter. Plants obtain the other 14 essential elements, called mineral nutrients, from soil. The mineral nutrients are classified as either macronutrients or micronutrients based on their relative abundance in plants. The six macronutrients, required in relatively large quantities, are N, P, K, S, Ca, and Mg. The eight micronutrients, required in relatively small quantities, are Cl, Fe, B, Mn, Zn, Cu, Ni, and Mo. Other nutrients such as Silicon (Si) have shown to be beneficial in crop growth and disease suppression, but are not essential for the plant to complete its life cycle.