1. American Society of Agronomy. 1982.Methods of soil analysis. Part 2, Chemical and microbiological properties., 2nd ed., Edited by: Page, A. L. 1159Madison, WI: American Society of Agronomy.
2. American Society of Agronomy. 1986.Methods of soil analysis. Part 1, Physical and mineralogical methods., 2nd ed., Edited by: Klute, A. 1188Madison, WI: American Society of Agronomy.
3. Atmospheric deposition and canopy interactions for conifer and deciduous forests in Northern Spain
4. Association of Official Analytical Chemists. 1990.Official methods of analysis of the Association of Official Analytical Chemists,, 15th ed, Edited by: Helrich, K. Vol. 1, 684Arlington, VA: Association of Official Analytical Chemists.