Changes During a Century in Trace Element and Macronutrient Concentrations of an Agricultural Soil

Surface soil and subsoil samples collected in 2012 from a long-term agronomic experimental field at Cornell University were digested in concentrated nitric-perchloric acid and analyzed for macronutrient and trace element concentrations by ICP-OES (inductively coupled plasma optical emission spectrometry) and ICP-MS (inductively coupled plasma mass spectrometry). Archived soil samples, taken from the same field nearly a century earlier (1913), were simultaneously analyzed by the same methods to determine any temporal trends in acid-soluble soil elemental composition that might have resulted from agricultural practices and amendments or from diffuse pollution at this semirural site. Modest increases in surface soil concentrations of several macronutrients (P, Ca, Mg, K) were observed between 1913 and 2012, probably attributable to fertilizer and lime amendments. Most trace elements showed either no significant concentration increase (Zn, Ba, Mn) or a small increase (Ni, Cr) in the surface soil. The greatest relative increase in surface soil trace metal concentrations was for arsenic (81%), followed by lead (40%) and cadmium (33%), although acid-soluble concentrations of these toxic metals in 2012 remained in the range considered typical for background levels in uncontaminated agricultural soils of this region. Cadmium measured in acid digests by ICP-OES was shown to overestimate total soil Cd at these low near-background concentrations, with both ICP-MS and a flame atomic absorption method using a preconcentration step for Cd in extracts providing results more consistent with known total soil Cd concentrations of certified standards.