17. Utility Functions Pedotransfer Functions (PTFs) Soil bulk density may be derived using one of the two PTFs below, depending on the availaability of other data. Equation 17.1 where: is the percentage of soil organic carbon. is the percentage of sand in the soil. is the percentage of clay in the soil. Equation 17.2 pH conversion Equation 17.3 where: is the pH determined in KCl solution. is the pH determined in water. is the pH determined in CaCl2 solution. is the pH of the soil solution. is the concentration of H+ in the soil solution. 16. The ALFAM2 Model Glossary