The long-term effect of sludge application on Cu, Zn, and Mo behavior in soils and accumulation in soybean seeds

Abstract

A long-term greenhouse column experiment using two soils of different textures amended with dewatered, composted and alkaline-stabilized sludges (biosolids) tested the effect of aging on trace metal solubility, mobility and crop uptake over 15 cropping cycles. Specifically, soil chemical properties and extractability of Cu, Zn and Mo were measured after each cropping cycle, and soybeans (Glycine max (L.) Merr.) grown as the final crop were analyzed for those metal concentrations in the seeds. Significant Cu loss from the surface soil through leaching, and increased Zn extractability resulting from soil acidification were evident in the early cropping cycles shortly after sludge application, with the degree of Cu mobilization and soil acidification strongly dependent on the type of soil and sludge. Liming to counter acidification in later cycles enhanced Mo extractability and bioavailability substantially, with some sludge treatments producing soybean seeds with Mo concentrations up to 5 times greater than the control. Aging effects were difficult to discern for trace metals in this long-term study, since soil pH changes caused by sludge and liming amendments dominated metal solubility and crop uptake.