Effects of foliar and soil application of sodium silicate on arsenic toxicity and accumulation in rice (Oryza sativa L.) seedlings grown in As-contaminated paddy soils

Figures & data

Table 1. The basic properties of the studied soils.

			OM	Fed	Feo	Available SiO2	Total As
Soil	pH	Texture	(g kg^−1)			(mg kg^−1)
Ca-L	5.7	Silty clay	29	11.0	4.0	108	16
Ca-H							114
Gd-L	5.0	Clay	74	22.9	7.6	249	17
Gd-H	5.2	Clay	55	22.8	9.7	243	129

Fe_d: dithionite–citrate–bicarbonate (DCB) extractable iron (Fe).

Fe_o: ammonium oxalate extractable Fe.

Available silicon dioxide (SiO₂): sodium acetate extractable Si.

Total arsenic (As): nitric acid-hydrogen peroxide digestion As.

Figure 1. The (a–d) pH and (e–h) redox potential of Chiwulan (Ca) and Guandu (Gd) soil with different silicon (Si) treatments during the flooding conditions (F: foliar application; S: soil application; the addition of 0-, 1- and 3-fold recommendation rates of Si in soil application and 0, 0.1 and 0.3% Si in foliar application are expressed as control, +Si and +3Si, respectively; Si was added on the 15th and 30th days).

Figure 2. The changes of silicon (Si) concentrations in soil pore water with (a–d) foliar application and (e–h) soil application of Si during the flooding conditions (F: foliar application; S: soil application; the addition of 0-, 1- and 3-fold recommendation rates of Si in soil application and 0, 0.1 and 0.3% Si in foliar application are expressed as control, +Si and +3Si, respectively; Si was added on the 15th and 30th days).

Figure 3. The changes of arsenic (As) concentrations in soil pore water with (a–d) foliar application and (e–h) soil application of silicon (Si) during flooding conditions (F: foliar application; S: soil application; the addition of 0-, 1- and 3-fold recommendation rates of Si in soil application and 0, 0.1 and 0.3% Si in foliar application are expressed as control, +Si and +3Si, respectively; Si was added on the 15th and 30th days).

Figure 4. The changes of arsenic (As) species concentrations in Chiwulan-high (Ca_-H) and Guandu-high (Gd_-H) soil pore water with (a–b) foliar application and (c–d) soil application of 3-fold recommendation rates of Si during the flooding conditions (Si was added on the 15th and 30th days).

Figure 5. The (a, c) shoot height and (b, d) shoot biomass of rice (Oryza sativa L.) seedlings grown in Chiwulan (Ca) and Guandu (Gd) soils with different silicon (Si) treatments. (F: foliar application; S: soil application; the addition of 0-, 1- and 3-fold recommendation rates of Si in soil application and 0, 0.1 and 0.3% Si in foliar application are expressed as control, +Si and +3Si, respectively).

Table 2. The concentrations of silicon (Si) in shoot and the concentrations of arsenic (As) in roots (removing iron plaque) and shoots of rice seedlings grown in Chiwulan (Ca) and Guandu (Gd) soils with different As contents and Si treatments.

Soil treatment		Si in shoot	As in root	As in shoot
		(g kg^−1)	(mg kg^−1)
Ca−L	F-control	9.8^b*	32^a	18.7^a
	F + Si	10.9^b	30^a	19.2^a
	F + 3Si	12.6^a	49^a	19.3^a
	S-control	12.8^c	62^a	18.0^a
	S + Si	23.6^b	34^b	12.1^b
	S + 3Si	29.1^a	29^b	8.4^c
Ca−H	F-control	8.4^a	403^a	31.7^a
	F + Si	9.4^a	449^a	30.5^a
	F + 3Si	8.3^a	425^a	34.9^a
	S-control	8.2^b	362^b	36.5^a
	S + Si	13.5^a	395^b	22.5^b
	S + 3Si	12.4^a	636^a	23.8^b
Gd−L	F-control	16.4^b	10^a	5.5^a
	F + Si	17.3^a	12^a	5.8^a
	F + 3Si	18.1^a	13^a	5.8^a
	S-control	18.7^c	16^a	7.0^a
	S + Si	26.0^b	15^a	6.0^b
	S + 3Si	34.6^a	15^a	5.1^c
Gd−H	F-control	9.8^a	142^a	16.7^a
	F + Si	8.6^a	145^a	15.4^a
	F + 3Si	9.5^a	79^b	16.0^a
	S-control	8.7^c	101^a	17.1^a
	S + Si	13.3^b	105^a	14.3^b
	S + 3Si	17.9^a	72^a	13.7^b

F: foliar application, S: soil application; the addition of 0-, 1- and 3-fold recommendation rates of Si in soil application and 0, 0.1 and 0.3% Si in foliar application are expressed as control, +Si and +3Si, respectively.

*Different letters in each column indicate a significant difference in the value among foliar and soil Si treatments, respectively based on the least significant difference (LSD) test (P < 0.05).

Table 3. The average silicon (Si)/arsenic (As) molar ratio in soil pore water, shoot biomass and total uptake of As in shoots of rice seedlings grown in Chiwulan (Ca) and Guandu (Gd) soils with different As contents and Si treatments.

Treatment soil		Average Si/As molar ratio	Shoot biomass relative to control (%)	Total uptake of As in shoot relative to control (%)
Ca−L	S-control	230	100	100
	S + Si	545	123*	83*
	S + 3Si	1432	132*	62*
Ca−H	S-control	15	100	100
	S + Si	29	91	56*
	S + 3Si	64	84*	55*
Gd−L	S-control	311	100	100
	S + Si	377	99	86*
	S + 3Si	475	101	74*
Gd−H	S-control	29	100	100
	S + Si	41	89	75*
	S + 3Si	58	80*	64*

S: soil application; the addition of 0-, 1- and 3-fold recommendation rates of Si in soil application are expressed as control, +Si and +3Si, respectively.

*There is a significant difference (P < 0.05) between +Si and control treatments.

Total uptake of As in shoot: As concentration in shoot (mg kg⁻¹) × shoot biomass (mg).