Answer:
1.Soils are named and classified based on their horizons. The soil profile has four distinct layers: 1) O horizon; 2) A horizon; 3) B horizon, or subsoil; and 4) C horizon, or soil base ((Figure)). The O horizon has freshly decomposing organic matter—humus—at its surface, with decomposed vegetation at its base.
2.Twenty elements are considered essential for plant growth because they are involved in metabolic functions required in the life cycle of the plant. Some, like carbon (C), oxygen (O), and hydrogen (H), can come from the air. Nitrogen (N) is made available to the plant from the air and soil. But most of the needed elements that are nutrients for plants come from the soil. They are not all equally important but all play a role in plant growth. Most needed are nitrogen (N), phosphorus (P), potassium (K), and sulphur (S). The others are calcium (Ca), iron (Fe), magnesium (Mg), manganese (Mn), zinc (Zn), copper (Cu), boron (B), molybdenum (Mo), chlorine (Cl), sodium (Na), cobalt (Co), nickel (Ni), and silicon (Si). They will be discussed in the next objective.
Explanation:
