Low-cadmium rice (Oryza sativa L.) cultivar can simultaneously reduce arsenic and cadmium concentrations in rice grains

Figures & data

Figure 1. Illustration of the three irrigation regimes that were applied to paddy fields at the nine sites after the mid-season drainage.

Table 1. Soil properties in the nine experimental fields.

				Total carbon	Total nitrogen	CEC	PAC	Fe		Av-Si	Ex-Mn	As	Cd
								Free Fe oxide	Non-crystalline Fe
Site	Soil type	Texture	pH	(g kg^−1)		(cmolc kg^−1)	(g P2O5 kg^−1)	(g kg^−1)		(mg kg^−1)
A	Mottled Gley lowland soil	SC	6.3	15.2	1.57	11.5	7.0	11.1	5.7	21.5	16.2	1.91	0.13
B	Medium-textured Gley lowland soil	SL	5.0	14.6	1.31	9.6	4.3	5.3	1.5	16.4	5.4	2.19	0.25
C	Haplic Gray lowland soil	L	5.9	11.5	1.10	9.5	5.6	13.0	7.6	19.0	18.5	1.26	0.18
D	Humic Gley lowland soil	SiCL	5.4	61.7	4.71	28.0	13.8	23.7	15.9	17.5	50.0	6.72	3.62
E	Cumulic Andosol	LC	6.6	86.7	6.33	46.0	21.0	37.4	19.9	39.0	3.8	1.82	0.12
F	Cumulic Wet Andosol	L	6.4	80.0	5.90	46.1	22.6	18.3	12.6	17.3	8.1	1.46	0.17
G	Mottled Gley lowland soil	SL	5.9	18.8	1.55	11.7	5.2	9.1	6.3	20.5	30.7	1.85	0.14
H	Grayed lowland paddy soil	CL	6.0	21.8	2.10	15.4	2.3	8.5	5.1	30.2	39.2	1.30	0.26
I	Grayed lowland paddy soil	L	6.2	21.7	1.99	10.0	6.9	6.1	6.2	18.7	3.0	2.70	2.80

Soil textures: SL, sandy loam; L, loam; CL, clay loam; SiCL, silty clay loam; SC, sandy clay; LC, light clay.

Chemical properties: CEC, Cation exchange capacity; PAC, phosphorus adsorption coefficient; Av-Si, available silicate; Ex-Mn, exchangeable manganese; As, 1 M HCl extractable As; Cd, 0.1 M HCl extractable Cd.

Figure 2. Effects of the three water regimes (FLD, flooding; AWD, alternate wetting and drying; WAS, water-saving) on soil redox potential (Eh) at the nine experimental sites. Soil Eh was recorded five times. Values are means ± standard deviation (SD; n = 3 to 5).

Figure 3. Effects of the three water regimes (FLD, flooding; AWD, alternate wetting and drying; WAS, water-saving) on arsenic (As) concentrations in the soil solution at the nine experimental sites. The soil solution was collected at the same time as the soil redox potential (Eh; Fig. 2) was determined. Values are means ± standard deviation (SD; n = 3).

Figure 4. Effects of the three water regimes (FLD, flooding; AWD, alternate wetting and drying; WAS, water-saving) on the concentrations of arsenic (As) and cadmium (Cd) in grains (brown rice) of (A) ‘Koshihikari’ and (B) ‘Koshihikari Kan No. 1’ grown at the nine experimental sites. Values are means ± standard deviation (SD; n = 3 to 4). Bars at a site labeled with different letters differ significantly (Tukey’s honestly significant difference test, p < 0.05).

Table 2. Two-way analysis of variance (ANOVA) for the effects of water regime, genotype and their interaction on grain arsenic (As) concentrations in rice (Oryza sativa L.) grown at each of the nine sites.

Source of variation	df	Percentage of total sum of squares
		2013					2014
		Site A	Site B	Site C	Site D	Site E	Site F	Site G	Site H	Site I
Water regime (W)	2	83.8**	85.4**	79.0**	52.3**	85.2**	70.8**	93.8**	72.4**	46.3**
Genotype (G)	1	0.3	0.0	0.0	0.0	1.6	0.8	0.1	6.0*	6.2
W × G	2	1.2	0.4	2.7	15.7	3.0	5.2	2.3	1.3	5.8

**, *: significant at P < 0.01 and P < 0.05, respectively.

All data were tested for a normal distribution using Levene’s test.

Figure 5. Effects of the three water regimes (FLD, flooding; AWD, alternate wetting and drying; WAS, water-saving) on the concentrations of manganese (Mn) in (A) grains and (B) straw. Values are means ± standard deviation (SD; n = 3 to 4).

Table 3. Grain yields (t ha⁻¹) of the two rice (Oryza sativa L.) cultivars grown under different water regimes (FLD, flooding; AWD, alternate wetting and drying; WAS, water-saving) at each of the nine sites.

		Grain yield (t ha^−1)
		2013					2014
Water regime	Genotype	Site A	Site B	Site C	Site D	Site E	Site F	Site G	Site H	Site I	AV
FLD	‘Koshihikari’ (control)	5.39	6.20	5.43	5.38	5.48	5.42	4.53	5.06	4.06	5.22 (100)
	‘Koshihikari Kan No. 1’	5.69	5.47	5.33	5.97	4.99	5.14	4.80	4.79	3.85	5.11 (98)
AWD	‘Koshihikari’	5.54	5.95	5.17	4.39*	4.75	5.67	4.67	5.33	4.41	5.10 (98)
	‘Koshihikari Kan No. 1’	5.82	5.28*	5.96	5.10	4.62	5.35	5.03	4.97	3.71	5.09 (98)
WAS	‘Koshihikari’	5.47	5.69	5.18	5.12	4.58	5.14	4.39	5.17	4.17	4.99 (96)
	‘Koshihikari Kan No. 1’	5.16	5.31*	5.05	5.70	4.26*	5.01	4.82	5.28	3.70	4.92 (94)

Values represent the means of two or three replicates. AV represents the average yield of each cultivar for all nine sites in a given water regime. The values in parentheses represent the average grain yield expressed as a percentage of the control (‘Koshihikari’ in FLD) yield.

Rice grain yields within each column (i.e., at each site) were compared with that of ‘Koshihikari’ in the FLD regime (the control group) using a one-tailed Dunnett’s test: *, significant at P < 0.05.

Table 4. Whole-grain ratio of rice (Oryza sativa L.) cultivars grown under different water conditions (FLD, flooding; AWD, alternate wetting and drying; WAS, water-saving conditions) at each of the nine sites.

		Whole-grain ratio (%)
		2013					2014
Water regime	Genotype	Site A	Site B	Site C	Site D	Site E	Site F	Site G	Site H	Site I	AV
FLD	‘Koshihikari’	33.0	38.5	26.2	89.0	41.3	68.1	65.7	81.1	66.5	56.6
	‘Koshihikari Kan No. 1’	27.7	27.4	23.9	91.4	37.6	67.4	63.3	79.3	64.4	53.6
AWD	‘Koshihikari’	32.7	40.5	21.2	90.1	37.3	68.8	69.4	81.0	66.3	56.4
	‘Koshihikari Kan No. 1’	31.6	22.2*	19.9	90.7	43.6	68.9	64.8	78.1	64.5	53.8
WAS	‘Koshihikari’	35.6	26.1	13.4	87.7	32.8*	71.7	68.3	83.1	65.9	53.8
	‘Koshihikari Kan No. 1’	27.6	18.9**	11.4*	87.4	27.8**	69.6	60.7	78.9	62.8	49.4

Values are the means of two or three replicates. AV represents the average value of each cultivar grown under a given water regime at the nine sites. Whole-grain ratio was determined using a rice inspector.

Whole-grain ratio values within a column (i.e., at a single site) were compared with that of ‘Koshihikari’ in FLD (the control group) using a one-tailed Dunnett’s test: **,*: significant at P < 0.01 and P < 0.05, respectively.