172
value of ess U in paddy field soil samples was 1.15 mg kg
−1
-dry and that in upland
field soil samples was 0.95 mg kg
−1
-dry.
To calculate ess U contribution to U in paddy field and upland field soil samples,
the concentration ratio between ess U to total U was then calculated for each soil
sample. The ess U/total U ratios are distributed normally for both paddy field and
upland field soil samples as shown in Fig. 7. The arithmetic mean values and one
sigma errors of ess U/total U were 0.49  ±  0.20 for paddy field soil samples and
0.46 ± 0.18 for upland field soil samples. Thus, from these results, on average it was
implied that about half of the total U was from U in phosphate fertilizers applied to
the paddy field and upland field soil samples.
Fig. 6 Distributions of
estimated ess U
concentrations in
agricultural soil samples
Table 3 Concentrations of total uranium and estimated ess U (mg  kg
−1
-dry) in agricultural soil
samples
Soil use
Total or excess
N
U concentrations
GM
GSD
Min.
Max.
Paddy field
Total U
98
2.70 × 10
0
1.3
1.50 × 10
0
1.06 × 10
1
ess U
95
1.15 × 10
0
2.0
4.30 × 10
−2
3.52 × 10
0
Upland field
Total U
139
2.35 × 10
0
1.5
3.07 × 10
−1
4.89 × 10
0
ess U
132
9.50 × 10
−1
2.3
4.32 × 10
−3
3.70 × 10
0
K. Tagami and S. Uchida