CERTIFICATION OF AN AIR-DRY SOIL FOR PH AND EXTRACTABLE NUTRIENTS USING 100TH MOLAR CALCIUM-CHLORIDE

The preparation of an air-dry river-clay soil as reference soil materi al for pH and extractable nutrients with a 0.01M calcium chloride (CaC l2) solution and the homogeneity testing are described. Recommended va lues for pH and the concentrations of ammonium-nitrogen (NH4-N), total soluble nitrogen (N), phosphorus (P), sodium (Na), potassium (K), and magnesium (Mg) using the unbuffered 0.01M CaCl2 are given. With respe ct to nitrate-nitrogen (NO3-N), the sample proved not to be sufficienc tly homogeneous. The certified soil sample has also been used as a sam ple in the International Soil-Analytical Exchange (ISE), a continuous proficiency testing scheme. The values found by the ISE laboratories c ompared well with the certified values.