SUBSURFACE LIMING AND METAL MOVEMENT IN SOILS AMENDED WITH LIME-STABILIZED BIOSOLIDS

Samples to a depth of Im were taken from two long-term biosolids held studies, to examine metal and alkalinity movement. The studies, locate d at the University of Maryland research facility in Beltsville, MD, h ad received biosolids in 1976 to 1978. One study, on a Christiana fine sandy loam (clayey, kaolinitic, mesic Typic Paleudult) had used a var iety of biosolids including Nu-Earth (a high-metals biosolids) applied at 50 and 100 Mg ha(-1) and limed-undigested, limed-digested, and lim ed-compost applied at 224 Mg ha(-1). The digested biosolids were also applied at 336 and 448 Mg ha(-1). The other study, on a Galestown sand (sandy, siliceous, mesic Psammentic Hapleudult), used limed-digested biosolids from the same treatment plant applied at 224 and 448 Mg ha(- 1). For both rates of biosolid application, soil pH was raised to >7.0 throughout the examined depth for the Galestown plots. pH increases w ere most pronounced for the limed-undigested biosolids (224 Mg ha(-1)) on the Christiana plots, with soil pH significantly higher than for t he calcareous control to 80 to 90 cm. Soil pH for this biosolids treat ment remained >5 to the 80 to 90 cm depth, while soil pH fell below 5 at the 40 to 50 cm depth for the calcareous control treatment. Movemen t of Pb, Zn, and Cu was detected in the high pH Nu-Earth treatments, w ith a distinct increase being observed for all three metals below 80 c m. Copper movement from the lime-undigested biosolids was detected bel ow 80 cm, and Zn movement also occurred for soils amended with the lim e-undigested and lime-compost biosolids. For the Galestown plots, dist inct movement of Zn, Pb, and Mn was detected to below 60 cm for the 44 8 Mg ha(-1) biosolids treatment. The observed movement of metal(s) and alkalinity may be linked to the formation of fulvic acid-metal comple xes that become increasingly more soluble at elevated pH. Although sta tistically significant, movement of metals was limited and occurred on ly after high rates of biosolids had been applied. There is no indicat ion that metal movement would occur in fields receiving agronomic rate s of biosolids.