Sorption of molybdenum in soils field-equilibrated with biosolids

Molybdenum (Mo) adsorption by soil is a function of several chemical factors, including added Mo load, solution pH, competing anion concentration, and iron (Fe) and aluminum (Al) oxide concentration in the soil, all of which can be changed by biosolids additions. The objective of this study was to determine the effects of biosolids on Mo sorption in two sandy Florida soils field-equilibrated with various biosolids. Molybdenum sorption was determined on surface samples of soils taken for up to 4 yr after biosolids amendment. Various parameters (soil pH, oxalate extractable-Fe and Al, and complementary ion concentrations) were measured and related to Mo sorption to explain biosolids effects. Biosolids application had only a small effect on Mo sorption as a result of added Fe and Al oxides in both soils studied. Molybdenum sorption was strongly related to soil pH and was maximized at soil pH values <4 to 5 for both soils studied. Although biosolids-additions had only a small effect on Mo sorption as a result of added Fe and Al oxides, biosolids (and other amendments) can change the pH of the soil environment, which can dramatically impact Mo retention and release.