Effect of nitrogen fertilization on radiocesium absorption in soybean

Abstract

Radioactive materials that were released during the nuclear accident contaminated the soil and agricultural products. It has become clear that potassium fertilization is effective for the reducing radiocesium concentrations in agricultural crops. However, apart from reports about potassium, few reports have examined how nitrogen (N), which has a large effect on crop growth, contributes to the radiocesium absorption. Focusing on this point, we studied the effect of nitrogen fertilizer on the radiocesium absorption in soybean seedlings. The concentration of radiocesium in the seed of soybean was higher in nitrogen-fertilized plants than in plants grown without fertilizer. The radiocesium concentration in the aboveground biomass increased as the amount of nitrogen fertilization increased. A comparison of the effects of the different forms of nitrogen treatment shows that the highest radiocesium concentration in the aboveground biomass occurred with ammonium sulfate (approximately 3.7 times the non-N), the next highest absorption occurred with ammonium nitrate (approximately 2.4 times the non-N treatment), followed by calcium nitrate (approximately 2.2 times the non-N treatment). Furthermore, the amount of radiocesium in soil extracts was highest with ammonium-nitrogen fertilization. Further study is required to clarify the factors that incur an increase in radiocesium concentration in response to nitrogen fertilization. Special care is required to start farming soybean on fallow fields evacuated after the accident or on fields where rice has been grown before, which tend to have higher available nitrogen than the regularly cultivated fields.