A field study on factors influencing Cd levels in soils and in grain of oats and winter wheat

Abstract

The influence of selected factors on Cd levels in soils and in grain of oats and winter wheat was investigated. Soil and grain were sampled at sites randomly distributed over Sweden. Organic soils generally had higher Cd contents and lower pH levels than mineral soils, and plants growing in organic soils tended to have higher Cd contents than plants growing in mineral soils. In mineral soils the amount of soil Cd extractable in 2M HNO3 was positively correlated with the pH and the contents of organic matter and clay. The studied variable best correlated with the Cd content of oat grain grown on mineral soils was the pH (negative correlation). Soil contents of organic matter, clay, HNO3-extractable Cd and Zn were also found to be significantly related to the Cd content in a stepwise regression analysis. In winter wheat grain, Cd content was best correlated with the HNO3-extractable Cd (positive correlation). Additional significant factors were pH, grain yield and contents of organic matter, clay and HNO3-extractable Zn. In winter wheat the presence of Zn reduced Cd uptake, and vice versa; no such mutually antagonistic relationship was apparent in oats. In oats, but not in wheat, it was possible to predict most of the differences in grain Cd content, caused by the factors described above, based on the variation in CaCl2-extractable soil Cd. Analysis of samples from field trials indicated that there were differences in Cd content between varieties of both crops. Variation in factors described generally explained most of the differences in soil- and grain Cd levels between regions.