APPLICABILITY OF 0.01 M CACL2 AS A SINGLE EXTRACTION SOLUTION FOR THE ASSESSMENT OF THE NUTRIENT STATUS OF SOILS AND OTHER DIAGNOSTIC PURPOSES

The applicability of 0.01 M CaCl2 solution as a single extraction agent for soils as a basis for fertilizer recommendation was tested on a variety of soils both from the Netherlands and from some tropical countries. Air-dry soil samples were subjected to extraction with 0.01 M CaCl2 and to several conventional extraction procedures, and the results were compared. In the soil suspensions pH was measured, whereas in the extracts Na, K, Mg, P, different extractable N-forms and Zn were measured. The values found in CaCl2 extracts are discussed in relation to results of other extraction procedures and as to their potential value in soil quality assessment. It is concluded that a a single extraction procedure with 0.01 M CaCl2 can be applied for fertilizer recommendation purposes. The possibility of determining different extractable N-forms (NH4, NO3, soluble organic N) significantly enhances the value of the method in predicting the N-fertilizer needs. Furthermore it was found that the concentration of Zn in 0.01 M CaCl2 extracts was a good indicator of phytotoxicity in a polluted area. Additional advantages of this extraction are low costs, simplicity and reproducibility.