Total selenium content of agricultural soils in Japan

Figures & data

Figure 1 Location of the sampling sites. •, volcanic soils; ○, non-volcanic soils.

Table 1 Number of samples for each soil type and land use

Soil type^†	Relevant soil type^‡	Paddy	Upland	Total
Peat soils	Hemists	5	3	8
Sand-dune Regosols	Psamments	0	1	1
Volcanogenous Regosols	Vitrands	1	4	5
Wet Andosols	Aquands	3	2	5
Non-allophanic Andosols	Udands	4	3	7
Andosols	Udands	5	36	41
Lowland Paddy soils	Aquepts	47	1	48
Gley Lowland soils	Aquents	25	3	28
Gray Lowland soils	Aquents	3	3	6
Brown Lowland soils	Ochrepts	0	14	14
Gray Upland soils	Aquepts	0	4	4
Dark Red soils	Udalfs	0	2	2
Red soils	Udults	0	1	1
Yellow soils	Udults	3	6	9
Brown Forest soils	Ochrepts	0	1	1
Total		96	84	180
^†By classification of cultivated soils in Japan (3rd approximation). ^‡By soil taxonomy (dominant type is indicated).

Table 2 General physico-chemical properties of the soil samples

Total	No.	pH	Total C (g kg^−1)	Total N (g kg^−1)	CEC (cmolc kg^−1)	Sand (%)	Silt (%)	Clay (%)
	180	5.75	31.7	2.51	20.1	47.7	28.3	24.0
Soil type^†
Peat soils	8	5.42	47.7	3.42	25.4	38.0	29.6	32.4
Sand-dune Regosols	1	6.71	6.3	0.53	3.3	95.9	2.2	1.9
Volcanogenous Regosols	5	5.66	27.2	2.15	13.4	72.3	16.1	11.5
Wet Andosols	5	5.59	62.3	4.02	31.4	49.3	27.4	23.3
Non-allophanic Andosols	7	5.59	64.4	4.63	27.7	46.9	29.3	23.8
Andosols	41	5.83	51.4	3.75	27.5	51.2	26.5	22.3
Lowland Paddy soils	48	5.73	22.2	1.97	15.4	49.7	28.6	21.8
Gley Lowland soils	28	5.56	24.1	2.05	18.6	41.8	30.3	27.9
Gray Lowland soils	6	5.71	18.3	1.74	13.1	56.5	24.5	19.1
Brown Lowland soils	14	5.79	18.1	1.63	18.8	47.0	32.6	20.5
Gray Upland soils	4	6.85	13.3	1.17	19.3	25.8	37.2	37.0
Dark Red soils	2	7.29	11.4	1.45	17.5	7.7	40.1	52.2
Red soils	1	3.96	1.8	0.47	17.9	16.1	17.8	66.0
Yellow soils	9	5.86	13.8	1.36	13.1	47.4	27.2	25.4
Brown Forest soils	1	5.52	9.0	0.81	18.2	31.0	34.4	34.5
Land use
Paddy	96	5.67	27.9	2.31	17.6	47.2	29.0	23.8
Upland	84	5.84	36.1	2.74	22.9	48.2	27.5	24.3
^†By classification of cultivated soils in Japan (3rd approximation). CEC, cation exchange capacity.

Figure 2 Reaction of selenite with 2,3-diaminonaphtalene.

Table 3 Minimum, maximum, median, arithmetic mean and geometric mean of the total selenium content of agricultural soils in Japan

Total	No.	Minimum (mg kg^−1)	Maximum (mg kg^−1)	Median (mg kg^−1)	Arithmetic mean (mg kg^−1)	Geometric mean (mg kg^−1)
	180	0.05	2.80	0.42	0.51	0.43
Soil type^†
Peat soils	8	0.31	0.96	0.61	0.61	0.57
Sand-dune Regosols	1	0.05	0.05	0.05	0.05	0.05
Volcanogenous Regosols	5	0.33	0.50	0.35	0.39	0.39
Wet Andosols	5	0.56	2.80	0.72	1.10	0.88
Non-allophanic Andosols	7	0.44	1.60	0.89	0.87	0.80
Andosols	41	0.25	1.32	0.70	0.72	0.66
Lowland Paddy soils	48	0.11	0.59	0.32	0.33	0.31
Gley Lowland soils	28	0.18	1.35	0.38	0.46	0.41
Gray Lowland soils	6	0.14	0.41	0.26	0.27	0.25
Brown Lowland soils	14	0.25	0.66	0.46	0.46	0.44
Gray Upland soils	4	0.31	0.39	0.34	0.35	0.34
Dark Red soils	2	0.34	0.37	0.36	0.36	0.35
Red soils	1	1.04	1.04	1.04	1.04	1.04
Yellow soils	9	0.14	0.50	0.35	0.35	0.33
Brown Forest soils	1	0.53	0.53	0.53	0.53	0.53
Land use
Paddy	96	0.11	2.80	0.36	0.46	0.38
Upland	84	0.05	1.35	0.50	0.57	0.50
^†By classification of cultivated soils in Japan (3rd approximation).

Figure 3 Frequency distribution of the total selenium content of agricultural soils in Japan.

Figure 4 Relationship between the total selenium content and the total carbon content.

Table 4 Correlation coefficients between the total Se content and the physico-chemical properties of the soils

	No.	pH	Total C	Total N	CEC	Sand	Silt	Clay
Total	180	−0.03	056**	056**	0.58**	−0.20**	0.06	0.26**
Paddy	96	−0.04	0.60**	0.59**	0.55**	−0.17	0.00	0.26**
Upland	84	−0.08	0.57**	0.57**	0.60**	−0.26*	0.18	0.28**
*P < 0.05; **P < 0.01. CEC, cation exchange capacity.