Copper in cultivated soils of Finland

Authors

• Markku Yli-Halla Department of Applied Chemistry and Microbiology, P.O. Box 27, FIN-00014 University of Helsinki, Finland

DOI: https://doi.org/10.23986/afsci.72721

Abstract

Soil samples from the plough layers of 105 fields in different parts of Finland were analyzed for Cu fractions. Vertical distribution of Cu was also studied in a smaller material. Total Cu (Cutot , HNO3-HCIO4-HF-H2SO4 digestion) in the surface soil ranged 6.9-97.4 mg kg-1 (mean 37.1 mg kg-1) and was highest in clay soils (mean 59.0 mg kg-1) and lowest in fine sand and moraine soils (mean 18.3 mg kg-1 ). Copper in the water-soluble, exchangeable and mainly organically bound fraction was extracted with 0.1 M K4P2O7 (Cupy), and Cu bound by poorly crystalline Fe, A and Mn oxides (Cuox) was dissolved subsequently with 0.05 M oxalate (pH 2.9). The average percentages of Cupy and Cuox were 18% and 12% of Cutot in mineral soils and 34% and 19% of Cutot in organogenic soils, respectively. Residual Cu (Cures ) incorporated in mineral lattices was calculated to constitute 70% and 47% of Cutot in mineral and organogenic soils, respectively. In two thirds of soils the potentially plant-available reserves of Cu (Cupy + Cuox) were more plentiful than those of Zn (Znpy + Znox). An acetic acid - ammonium acetate - Na2EDTA solution used in routine soil testing extracted 56% and 71% of the sum of Cupy + Cuox in mineral and organogenic soils, respectively. In soil profiles, CuEDTA was higher in the plough layer than in the subsoil but a few soils rich in Cutot had abundant reserves of CuEDTA below the rooting depth of annual field crops.