Soil is a mixture of topsoil soft minerals and organic matter which acts as a natural medium for plant growth. The bottom of the soil contains nothing but water - minerals - (gas , silicon , zircon, etc.) 45% ; Organic matter - (animal carcasses , rotten roots of plants) 5% ; Wind - 25% ; Water - 25% ; The mineral crust was first formed by rocks. It is then broken down into small pieces or units in the process of rock erosion. This part of the soil is composed of sand , silt and clay particles. The process of rock erosion releases the above particles and essential nutrients like nitrogen , phosphorus , potassium , calcium and other nutrients into the soil. The mineral content of the soil is 45%. Organic matter Soils contain 1-2% organic matter whereas frost soils contain 2-5% organic matter. All these organic matter come to the soil from the remains and excrement of plants and animals. Organic matter is used as soil binding material. Although the amount of organic matter in the soil is very low, it greatly controls the quality of the soil. Air is 25% in soil and water is 25% in soil. Most of the soil pores are filled with water during heavy rains or irrigation. But during dry or drought, those pores are filled with air. Soil air contains more carbon dioxide and water vapor than atmospheric air but contains less oxygen. The main function of air is to participate in the process of respiration.