TRENDS AND ANNUAL VARIATIONS IN CD CONCENTRATIONS IN GRAIN OF WINTER-WHEAT

Grain samples from four varieties of winter wheat, grown within the same limited area, one of them during the entire period 1918-1980, were analysed for Cd and some other elements for comparison. Two types of variation were found for Cd, namely annual fluctuations and systematic increase with time. The annual fluctuations in Cd content were about twice as high as for the other elements investigated, as expressed by the standard deviation as a percentage of the averages. They were most likely caused by climatic fluctuations during the growing season and by the variation in soil factors like pH and soil type when the growing was alternated between adjacent fields. There was a significant positive correlation between the Cd and Zn contents, despite different time trends. The Cd content as independent of the yield level. The time trend, meaning more than a doubling of the Cd content in grain during the period 1918-1980, may be partly due to increased solubility and availability to plants of the soil Cd, and partly to increasing soil levels. Alterations in solubility may have been brought about by changes in fertilization and soil management practice during the period, and increasing soil levels are most likely caused by the continuous supply of Cd in phosphorus fertilizers and from the atmospheric deposition.