The soil HCl-extractable Cd concentration varied little among
treatments not receiving manure applications (Fig. 3). Concentrations
from 25.0 to 689 mg HCl-extractable Cd kg − 1 were detected in
topsoil of RSES. By 2006 the HCl-extractable Cd concentration in topsoil of the OM and ONPK treatments exceeded that in the control
plots by about 4.5- and 5.4-fold. No significant differences in HClextractable Cd concentration were found between the control treatment and the treatments receiving chemical fertilizer applications.
This indicates that 16 years of manure applications had increased