SOME FACTORS AFFECTING THE DETERMINATION OF HOT-WATER-SOLUBLE BORON FROM PODZOL SOILS USING AZOMETHINE-H

Abstract

A study was conducted on some factors affecting the colorimetric determination of B using the azomethine-H reagent on soils from Prince Edward Island. Two fine sandy loam soils (A and B) were used for the main study and additional soil samples varying in organic matter (OM) were used to assess the role of OM. Soils containing less than 3.0% OM and 3.1–4.1% OM required 0.4 g and 0.8 g charcoal per 25 g soil, respectively, to produce clear hot-water extracts. Quantities of greater than 0.8 g charcoal were necessary to produce clear extracts from soils containing more than 4.1% OM. Colored hot-water extracts of soil resulted in higher absorbance than those hot-water extracts treated with charcoal as measured at 430 mμ. Additions of 0.8 and 1.6 g charcoal or greater to the soils (A and B) resulted in considerably lower recoveries of B as noted by comparing the absorbance obtained using 0.4 and 0.8 g, respectively. Storage of azomethine-H up to 7 days did not affect the absorbance of the B-azomethine-H complex. One hour after the addition of azomethine-H, a maximum absorbance was found which persisted for up to 4 h. The percent recovery of B added to the two soils was about 10–12% less using azomethine-H as compared to those obtained using the carmine method. However, the mean hot-water-soluble B contents of 10 soils as measured using the carmine and azomethine-H reagents were 0.70 and 0.66 ppm. Pure B solutions when boiled with charcoal resulted in losses of B added. Such losses of B increased with increasing rates of charcoal.