Effect of NO-₃ on the fate of ⁹⁹TcO-₄ in the soil plant system

This work was undertaken to study the effect of NO-₃ fertilization on the uptake of ⁹⁹TcO-₄ by plants. Rye-grass (Lolium perenne) was grown in a growth chamber on a silty loam soil to which were added increasing quantities of ammonium nitrate (21, 50 and 100 mg N kg^-1). Soil samples were then amended with ⁹⁹TcO-₄ at a constant level of 29.6 k Bq kg-1 dry weight. Total initial NO-₃ content was 43.3, 57.8 and 82.8 mg N kg^-1, and total NH+₄ content was 24.7, 39.2 and 64.2 mg N kg^-1. Three cuts were made at 4-week intervals, and aerial biomass was analysed for total ⁹⁹Tc and N. Results showed that total uptake of ⁹⁹Tc was decreased by increasing mineral N additions at the first cut, as mineral nitrogen was not a limiting factor for plant growth at this stage. Technetium-99 content in plants varied from 64% of the total applied ⁹⁹Tc with the lowest NO-₃ content to 31% with the highest. However, at the third cut, cumulative ⁹⁹Tc uptake reached the same level for the three treatments (80-83%) with no further effect of initial N applications, as NO-₃ was depleted in the soil. Therefore, ⁹⁹TcO-₄ was diluted in the pool of soil NO-₃ and was absorbed proportionally to nitrate by rye-grass