CHEMICAL FRACTIONATION OF SOIL BORON .1. METHOD DEVELOPMENT

A chemical fractionation scheme for soil boron was investigated by mea suring the amounts of B extracted from minerals and synthetic soils am ended with B. The scheme fractionated B into five fractions - readily soluble (solution plus non-specifically adsorbed), specifically adsorb ed, oxide bound, organically bound and residual. These five fractions were extracted by 0.01 M CaCl2, 0.05 M KH2PO4, 0.2 M acidic NH4-oxalat e, 0.02 M HNO3-30% H2O2, and 1:4:5 HNO3-HF-HCl, respectively. The meth odology was tested on goethite and clay mica and three synthetic soils containing mixtures of goethite, clay mica, humic acid, calcite, and quartz sand and amended with three levels of B. Specifically adsorbed and oxide bound B were significantly correlated with the content of go ethite in the synthetic soils, while residual B was significantly corr elated with the content of clay mica. The recovery of extracted B, est imated as the percentage of total fractions over total B content in mi nerals and synthetic soils, ranged from 85 to 104%, with a mean of 97% . The overall results obtained with the fractionation scheme were deem ed satisfactory as to sensitivity and precision for B fractionation.