Total Phosphorus is 20%, available phosphorus 7%, CaO is 31%, SiO2 is 26%. The product is derived from rock phosphate. Phosphate (P2O5) is one of the major macronutrients along with Nitrogen (N), and Potash (K2O). Some soils may need large initial applications (up to 1000 lbs/acre) to bring the soil to a point where it will release sufficient phosphate to the plant. After the soil is brought to balance, only maintenance amounts (100-200 lbs/acre) are usually needed.