Reduction of the risk of arsenic accumulation in rice by the water management and material application in relation to phosphate status

Figures & data

Table 1. Effect of the material application on the growth of rice at heading stage in the concrete frame experiment.

	Plant length (cm)	Number of tiller	SPAD
Control	92.7 ± 0.98 a	21.8 ± 0.7 a	38.9 ± 0.3 a
Fe	92.5 ± 1.42 a	21.3 ± 0.5 a	40.9 ± 0.4 b
Si	94.9 ± 1.81 a	22.1 ± 0.6 a	39.0 ± 0.6 a
Analysis of variance
	p = 0.4500	p = 0.6478	p = 0.0045***

Note: Data are means ± SE; n = 9. Different letters within a column indicate significant differences by Ryan test at p < 0.05.

*** Represents significance at the 0.001 probability level.

Table 2. Concentrations of As, Cd, and P in the tiller at heading stage in the concrete frame experiment.

	As (mg kg^−1)	Cd (mg kg^−1)	P (mg kg^−1)
Control	4.77 ± 0.32 a	0.102 ± 0.021 a	4418 ± 666 a
Fe	3.16 ± 0.45 b	0.085 ± 0.016 a	3743 ± 681 a
Si	3.74 ± 0.43 ab	0.100 ± 0.021 a	4537 ± 403 a
Analysis of variance
	p = 0.0310*	p = 0.7863	p = 0.6046

Note: Data are means ± SE; n = 9. Different letters within a column indicate significant differences by Ryan test at p < 0.05.

* Represents significance at the 0.05 probability level.

Table 3. The grain yield and biomass production of straw at harvest in the concrete frame experiment.

Treatment		Grain yield (g m^−2)	Dry weight of straw (g m^−2)
Start period of drainage (D)	Heading	960 ± 43	1142 ± 38
	10 days after heading	931 ± 21	1072 ± 40
	20 days after heading	926 ± 32	1245 ± 65
Material application (M)	Control	978 ± 27	1143 ± 24
	Fe	914 ± 38	1084 ± 45
	Si	925 ± 32	1236 ± 70
Analysis of variance	D	ns	ns
	M	ns	ns
	D × M	ns	ns

Note: Data are means ± SE; n = 9.

ns, not significant at the 0.05 probability level.

Table 4. Analysis of variance (two-way ANOVA) on the concentration of As, Cd, and P in the grain and straw at harvest in the concrete frame experiment.

	As		Cd
	Grain	Straw	Grain	Straw
Start period of drainage (D)	0.0056**	0.3587	<0.0001	0.0003***
Material application (M)	0.0376*	0.1292	0.1890	0.9499
D × M	0.1742	0.2460	0.3639	0.5698

* Represents significance at the 0.05 probability level.

** Represents significance at the 0.01 probability level.

*** Represents significance at the 0.0001 probability level.

Figure 1. Effects of the start period of drainage after heading and the application of materials on the concentrations of Cd (a) and As (b) in rice grain at harvest (mean ± SE; n = 9). Different letters within each treatment indicate significant difference by Ryan test at p < 0.05.

Table 5. The concentration of P in the grain and straw and the concentration ratio of grain to straw at harvest in the concrete frame experiment.

		P (mg kg^−1)
		Grain	Straw	Grain/straw
Start period of drainage (D)	Heading	3322 ± 49 a	2071 ± 117 a	1.66 ± 0.10 a
	10 days after heading	3415 ± 58 a	1964 ± 88 a	1.78 ± 0.09 a
	20 days after heading	3208 ± 74 a	2345 ± 97 a	1.39 ± 0.06 b
Material application (M)	Control	3328 ± 53 a	2077 ± 80 a	1.63 ± 0.07 a
	Fe	3324 ± 41 a	2219 ± 126 a	1.55 ± 0.10 a
	Si	3293 ± 65 a	2085 ± 129 a	1.65 ± 0.12 a
Analysis of variance	D	0.0728	0.0957	0.0351*
	M	0.9035	0.6489	0.7586
	D × M	0.2053	0.5168	0.4583

Note: Data are means ± SE; n = 9. Different letters within a column indicate significant differences by Ryan test at p < 0.05.

* Represents significance at the 0.05 probability level.

Figure 2. Relationships between the P concentration ratio of grain to straw and the As concentration in grain in (a) control (no material application; circles), (b) Fe application (squares), and (c) Si application (triangles). **p < 0.01, *p < 0.05. Open symbols: drainage started from heading. Gray-filled symbols: drainage started 10 days after heading. Black-filled symbols: drainage started 20 days after heading.

Table 6. Effects of As application period and P level in culture solution after heading on the concentration of As and P in the grain and straw at harvest in solution culture experiment.

		As			P
Treatments		Grain (mg kg^−1)	Straw (mg kg^−1)	Grain/straw	Grain (mg kg^−1)	Straw (mg kg^−1)	Grain/straw
As application (A)	Whole growth period	0.486 ± 0.035 a	14.1 ± 1.2 a	0.036 ± 0.004	3844 ± 148 a	8485 ± a	0.463 ± 678 a
	Before heading	0.126 ± 0.023 c	3.9 ± 0.5 c	0.033 ± 0.006	4209 ± 142 a	7745 ± a	0.589 ± 962 b
	After heading	0.253 ± 0.042 b	10.5 ± 0.5 b	0.025 ± 0.004	3991 ± 144 a	7943 ± a	0.519 ± 655 ab
P level (P)	Standard	0.335 ± 0.049 a	10.3 ± 1.8 a	0.034 ± 0.003	4123 ± 123 a	9597 ± a	0.433 ± 249 a
	Half of standard	0.242 ± 0.064 b	8.7 ± 1.4 a	0.029 ± 0.004	3906 ± 117 a	6518 ± b	0.615 ± 354 b
Analysis of variance
	A	<0.0000***	<0.0000***	0.1522	0.2583	0.03539	0.0448*
	P	0.0079**	0.0725	0.0777	0.2304	<0.0000***	<0.0003***
	A × P	0.1071	0.1965	0.0448	0.7899	0.2519	0.0813

Different letters within a column indicate significant differences by Ryan test (As application, n = 6; P level, n = 9, p < 0.05).

* Represents significance at the 0.05 probability level.

** Represents significance at the 0.01 probability level.

*** Represents significance at the 0.0001 probability level.

Figure 3. Relationships between the P concentration ratio of grain to straw and the As concentration in grain in the solution culture experiment conducted with different application periods of As and different levels of P in culture solution. (a) standard P concentration, (b) half of the standard P concentration. *p < 0.01. Open symbols: As amendment before heading. Gray-filled symbols: As amendment after heading. Black-filled symbols: As amendment for the entire growth period.