Selenium in soil and winter wheat : analysis of soil-crop-inventory data

Abstract: This study examined what variables that affect selenium (Se) concentrations in Swedish soils and winter wheat grains. The possibility and necessity of a Swedish Se-fortification program is also discussed. Analysis of data from the Swedish environmental monitoring program on arable land showed that Se concentrations in soils were significantly positively correlated with the organic matter in soil, more specifically with carbon (R=0.56; p < 0.001 n=287), nitrogen (R=0.47; p < 0.001; n=287) and sulphur R=0.58; p < 0.001; n=287). There was also a positive correlation with the cadmium concentrations in soil (R=0.32; p < 0.01; n=287). Weaker relationships were found between selenium concentrations in soil and texture, negative correlation with sand content (R=-0.23; p < 0.05; n=286) and positive correlation with clay content (R=0.26; p < 0.05; n=286). For selenium in the grain, a strongly significant positive relationship was found with pH in the soil (R=0.41; p < 0.001; n=285) and with the total concentrations of selenium (R=0.31; p < 0.01; n=285) and cadmium (R=0.32; p < 0.01; n=287) in the soil. There were no evidence for anion competition between selenium and other oxyanions. There was a strong negative correlation between Se/Cd ratios and cadmium concentrations in grain (R=-0.20; p < 0.001; n=285), suggesting that more selenium in relation to cadmium in the soil affects cadmium concentrations in crops. This implies that selenium fertilization may be a possibility to decrease cadmium concentrations in crops. The mean concentration of selenium in winter wheat grains in Sweden is 0.02 mg/kg. Dietary selenium intake among adults in Sweden today is below the recommended amount. Desirable selenium concentrations in grain were calculated if all cereal crops were to be fertilized amounting to 0.085 mg/kg and if only wheat were to be fertilized to be 0.145 mg/kg. Selenium deficiency in the diet is an overlooked problem in Sweden today and needs further attention.