Impact of long-term cultivation on the status of cadmium in chernozemic soils
Cadmium (Cd) from the soil can accumulate in our bodies via the consumption of our crops and cause serious health problems. While it has been documented that long-term cultivation affects physical and chemical properties of soil, little is known about its effect on the phytoavailability, solid-phase speciation, and profile distribution of soil Cd. The objectives for this study were to determine the effect of long-term cultivation on: (1) a cadmium availability index (CAI) that reflects phytoavailable Cd for durum wheat, and related soil properties, (2) the solid-phase species of soil Cd and relationships between the CAI and the solid-phase species of soil Cd and related solid-phase soil component properties, and (3) the profile distribution of total soil Cd in the past, and the profile distribution of total soil Cd over the next 100 years. One Orthic Chemozemic soil profile was investigated from a virgin and an adjacent long-term cultivated field at eight sites in the Brown, Dark Brown, and Black soil zonesof Saskatchewan, Canada. Long-term cultivation significantly decreased the CAI. A decrease in total Cd, total Zn, and CEC, and an increase in aromaticity of the soil organic matter and soil pH all contributed to the decrease in the CAI. Both the virgin and cultivated soils had the same solid-phase Cd species with the same order of relative abundance: metal-organic complex-bound > easily reducible metal oxide-bound > H2O2 extractable organic-bound > crystalline metal oxide-bound > exchangeable. However, metal-organic complex-bound Cd and H2O2 extractable organic-bound Cd decreased significantly with long-term cultivation. In the virgin soils two solid-phase Cd species correlated significantly with the CAI: exchangeable Cd (r = 0.93) and easily reducible metal oxide-bound Cd (r = -0.88). In the cultivated soils three solid-phase Cd species correlated significantly with the CAI: exchangeable Cd (r = 0.95), metal-organic complex-bound Cd (r = 0.71), and crystalline metal oxide-bound Cd (r = 0.86). For both the virgin and cultivated soils, the concentration of A horizon Cd > C horizon Cd > B horizon Cd. In the past, A horizon Cd concentration decreased significantly with long-term cultivation. However, it is estimated that in 100 years, with the use of phosphate fertilizer made from Idaho ore, the total A horizon Cd content in these soils could be 3.5 times higher and reach a concentration of 1.18 mg Cd kg-1 soil which is in the critical region where the phytoavailability of soil Cd could increase dramatically. The present study has advanced the frontiers of knowledge on the effect of long-term cultivation on the Cd content and distribution in the soil profile, its phytoavailability index, solid-phase species, and the soil properties related to its phytoavailability. Extending research such as this to other major agricultural soil types and farming practices will assist in the development of innovative management strategies to curtail Cd contamination of the terrestrial food chain.
tillage, soil science, geochemistry, metals, soil absorption and adsorption, agriculture
Doctor of Philosophy (Ph.D.)