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10.0 REFERENC S <br /> 1. Black, Charle Allen; Methods of Soil Analysis; American Society of Agronomy: <br /> Madison, WI, 1973. <br /> 2. National Bureau of Standards, Standard Reference Material Catalog, 1986-87, Special <br /> Publication 2 0. <br /> 9045D - 4 Revision 4 <br /> November 2004 <br />