Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: January 10, 1997
Publication Date: N/A
Interpretive Summary: An understanding of B chemistry is important for avoiding B toxicity to crops grown in arid regions, as many soils in these regions contain elevated concentrations of B. Management of these soils, especially reclamation, must take into account both the quantity of B present as well as its rate of release to the solution. In light of this requirement we examine the sources of B present in soils, in terms of both short term and long term release to the solution phase. Short term, or relatively rapid release is attributed to desorption of B from the surfaces of oxides and clays. Slow release of B from arid zone soils may be related to incorporation into poorly crystallized aluminosilicate minerals. In the soils examined, long term release of B to solution appears likely to occur from a seldomly characterized clay mineral, rather than from illite, as is commonly assumed. Knowledge of the quantity of B in the various pools will assist in development of reclamation practices.
Technical Abstract: The study of B chemistry is especially necessary because for plants B has the most limited range between toxicity and nutrient deficiency of all the micronutrients. Boron toxicity problems are common in arid zone soils. Management of high B containing soils requires that we know the long term release of B from these soils, both from structural incorporation as well as desorption. Evaporation of surface waters results in waters of either Na-Cl-CO3 or Ca-Mg-Na-Cl composition. This in turn affects the mineralogy of the precipitated B deposits. Illites are generally considered to be the source of B which results in elevated concentrations of B in solution (tourmaline dissolution being so slow as to be a negligible B source). Recent work has established that important pools of B may reside in poorly crystallized minerals such as allophane. Release of B from these minerals is difficult to distinguish from slow desorption of B from clay and oxide minerals. Slow kinetics of desorption is consistent with FTIR study which indicated bidentate inner sphere complexation of B onto Al oxides. In addition soils from the Central Valley of CA, with elevated concentrations of soluble and total B, were determined to contain palygorskite-a Mg clay mineral formed in high salinity environments. Dissolution kinetics established a good correlation between structural B release and Mg release, providing additional evidence for palgorskite as an important B source.