EXTRACTION OF BORON FROM SOIL BY MICROWAVE-HEATING FOR ICP-AES DETERMINATION

Extraction with hot water is the most widely used procedure to determi ne boron (B) in soils for the diagnosis of the nutrient availability f or plants. However, this procedure is tedious for routine conditions a nd requires some special precautions. An alternative extraction proced ure was developed, consisting in the extraction of B with a 1.25 g/L s olution of barium chloride (BaCl2) or with water heated in a domestic microwave oven. Boron was determined either by inductively coupled arg on plasma emission spectrometry (ICP-AES) and by spectrophotometry wit h azomethine-H. Good correlations were found between the extraction by boiling water under reflux and the extraction by the microwave heatin g for 13 Brazilian soils, and the contents of B obtained by spectropho tometry did not differ significantly from those obtained by ICP-AES. C onsidering the calculated standard deviations, it can be concluded tha t microwave heating followed by ICP-AES determination is an adequate p rocedure for the determination of hot water extractable B in soils.