Spatial Distribution of Cadmium and Zinc in Soils of Northern North Dakota

Soil Cd and Zn were strongly correlated and characterized by generally similar spatial distribution.Agricultural soils on the Pembina Escarpment and Red River Valley had naturally high total and DTPA‐extractable Cd and Zn.Many soils of the Pembina Escarpment and Red River Valley had naturally high organic C and CEC.Parent materials of high clay content were derived from shale‐enriched glacial till or colluvium, alluvium, and lacustrine deposits.Distribution of Cd and Zn followed the distribution of parent materials and soil CEC, organic carbon, and texture. Cadmium and zinc are trace elements with many geochemical similarities, but Cd is non‐essential and potentially toxic to humans and animals, whereas Zn is an essential micronutrient. Understanding the distribution and availability of these elements in soils is necessary for managing their availability to plants and the accumulation of Cd in edible crops, such as durum wheat. We studied the distribution of Cd and Zn in agricultural soils across the 18 counties of northern North Dakota because this region produces the majority of durum wheat grown in the United States, and many varieties of durum tend to accumulate undesirable levels of Cd in grain. Surface and subsurface soils were sampled and analyzed for concentrations of total and DTPA‐extractable Cd and Zn, pH, organic carbon (OC), and cation exchange capacity (CEC). Soil parent materials were classified based on information in the Soil Survey Geographic database for North Dakota. The spatial dependencies of the concentrations of Cd and Zn, and their (Cd/Zn) were investigated by modeling spatial variograms, and the results used for kriging or co‐kriging to prepare maps of the distribution of these characteristics across northern North Dakota. The distribution of Cd and Zn in these glaciated soils of northern North Dakota appears to be determined largely by the distribution of soil parent materials and by the soil properties CEC, OC, and soil texture. Relatively high levels of Cd and Zn were found in soils derived naturally from clayey shale‐enriched till, colluvium, and lacustrine deposits near the Pembina Escarpment or in the Red River Valley.