EXTRACTION OF BORON FROM CSSC REFERENCE SOILS BY HOT WATER, DILUTE CaCl2 AND MANNITOL-CaCl2 SOLUTIONS

Abstract

Soils were extracted by hot water, dilute CaCl₂, and by mannitol-CaCl₂ solutions and boron was determined by either azomethine-H or the curcumin method. Results were strongly method dependent; in particular results by the simplest method, mannitol-CaCl₂, were generally lower and not highly correlated (r = 0.64) with those by the recommended procedure. This procedure involves extraction with hot distilled H₂O (2:1 solution:soil), centrifugation, filtration, color development with azomethine-H and correction for background color. Extractable boron values by this procedure ranged from 0.1 to 1.4 mg kg⁻¹. Background color can be further reduced by the substitution of 0.02 M CaCl₂ for distilled water. Key words: CSSC reference soil samples, hot-water-soluble boron