1. Standard test method for pH of soil;American Society for Testing and Materials,1995
2. Test method for laboratory determination of water (moisture) content of soil and rock. Designation D2216-92. Philadelphia, PA;American Society for Testing and Materials,1998
3. Test method for pH of peat materials, Designation D2976-71, Philadelphia, PA;American Society for Testing and Materials,1998
4. Standard classification of soils for engineering purposes;American Society for Testing and Materials,2000
5. Soil humus fractions;Anderson,1993