Soil boron fractions and their relationship to soil properties

An understanding of soil nutrient pools and their relationship to soil properties and to soil test values should underpin soil tests, but few studies of this type have been conducted for soil B. Boron was fractionated by sequential extraction in 13 soils collected from north (47 degreesN) to south (20 degreesN) in eastern China. The nonspecifically adsorbed B (NSA-B) and specifically adsorbed B (SPA-B) comprised <1% of total B. By contrast, B occluded in Mn oxyhydroxide (MOH-B), in amorphous Fe and Al oxides (AMO-B) and in crystalline Fe and Al oxides (CRO-B) comprised from 0.01 to 7.6% of total B. The content of the NSA-B fraction significantly decreased with increasing mean annual rainfall of the site and increased with increasing soil pH and exchangeable Ca. The MOH-B fraction was positively correlated with soil pH and cation-exchange capacity (CEC), and negatively with rainfall and temperature. The AMO-B fraction was significantly related to amorphous Fe2O3 and rainfall. The CRO-B fraction was positively correlated with pH and exchangeable Ca, but not with crystalline Fe2O3. The SPA-B fraction was not correlated with any soil properties or climate factors. These results emphasize that the forms of B in Chinese soils were distinctly different from those in soils of southeast USA and Greece.