Boron fractionation was studied in relation to its availability to corn in 14 soils (49)
. Up to 0.34%
of the total boron was in a water-soluble form, 0 to 0.23% was nonspecifically adsorbed (exchangeable),
and 0.05 to 0.30% was specifically adsorbed. Jin et al. (49)
reported that most of the boron
available to corn was in these three forms, and that boron in noncrystalline and crystalline aluminum
and iron oxyhydroxides and in silicates was relatively unavailable for plant uptake. For the
identification of different pools of boron in soils, Hou et al. (50)
proposed a fractionation scheme,
which indicated that readily soluble and specifically adsorbed boron accounted for +
2% of the total
boron. Various oxides-hydroxides, and organically bound forms constituted 2.3 and 8.6%, respectively.
Most soil boron existed in residual or occluded form. Recent studies by Zerrari et al. (51)
showed that the residual boron constituted the most important fraction at 78.75%.