Speciation of phosphorus accumulated in fertilized cropland of Aichi prefecture in Japan with different soil properties by sequential chemical extraction and P K-edge XANES

Figures & data

Table 1. Number of samples analyzed for each soil group

Soil classification^†			Relevant soil type^‡	Number of samples
Soil groups	Soil subgroups Soil series groups	Abbreviation
Brown Lowland soils		BLn	Ochrepts	10
Brown Lowland soils	humic	BLh	Ochrepts	3
Regosolic Lowland soils		RL	Psamments	28
Gray Lowland soils		GL	Aquents	18
Yellow soils	coarse-textured	Yc	Udults	16
Yellow soils	medium-textured	Ym	Udults	23
Yellow soils	fine-textured	Yf	Udults	24
Brown Forest soils		BF	Ochrepts	15

^†By Classification of Cultivated Soils in Japan, third Approximation (Cultivated soil classification committee 1995). ^‡By Soil Taxonomy (dominant type is indicated) (Soil Survey Staff 2014).

Figure 1. Map of sampling locations. Sample names on the map indicate the samples analyzed by P K-edge XANES. The distribution of Non-allophanic Andosols was revised based on Kato (1970) and Matsuyama et al. (1994)

Table 2. Physicochemical properties of soil samples for each soil group

Soil groups (n)	pH		ExCa		TC		Clay		Alo		Feo		Alo+1/2Feo		Ald		Fed
			mmolc kg^−1		g kg^−1
BLn (10)	6.9	a	51	bc	9	bc	89	cd	3.2	b	2.9	ab	4.6	b	2.3	bcd	5.5	bc
BLh (3)	5.5	b	120	a	53	a	181	bc	8.7	a	4.8	a	11.1	a	4.3	ab	6.9	abc
RL (28)	6.3	ab	44	c	8	c	56	d	0.9	d	1.5	c	1.7	de	1.4	c	4.2	c
GL (17)	6.6	ab	94	a	10	b	101	cd	1.5	cd	3.3	a	3.1	c	2.6	bd	6.1	bc
Yc (16)	6.2	ab	27	c	10	bc	107	cd	1.0	d	1.2	c	1.5	de	1.8	c	6.5	bc
Ym (23)	6.5	ab	42	c	15	b	192	b	1.3	cd	1.4	c	2.0	de	2.9	abd	12.2	a
Yf (24)	6.0	b	88	a	15	b	336	a	1.6	c	1.9	bc	2.6	cd	3.7	a	14.7	a
BF (15)	6.9	a	82	ab	10	bc	196	b	0.9	d	0.9	c	1.4	e	2.4	bd	10.9	ab

BLn: Brown Lowland soils; BLh: Brown Lowland soils with humic layer; RL: Regosolic Lowland soils; GL: Gray Lowland soils; Yc: Yellow soils coarse texture; Ym: Yellow soils medium texture; Yf: Yellow soils fine texture; BF: Brown Forest soils. ExCa: exchangeable Ca; TC: total carbon; Al_o and Fe_o: Al and Fe extracted by acid ammonium oxalate, respectively; Al_d and Fe_d: Al and Fe extracted by dithionite-citrate bicarbonate, respectively. Different letters indicate significant differences (p < 0.05) among soil groups.

Table 3. Average value of P stock in soils evaluated by chemical extraction (mg P kg⁻¹)

Soil groups (n)	Total P		Truog P (ratio to TP)			Sequential P fractionation
						AA-P (ratio to TP)			NH4F-P (ratio to TP)			NaOH-P (ratio to TP)			Organic P (ratio to TP)
BLn (10)	2,189	bc	567	b	(26)	603	a	(28)	1,211	b	(55)	155	ce	(7)	210	b	(10)
BLh(3)	4,916	a	679	ab	(12)	759	a	(13)	2,982	a	(60)	505	a	(13)	567	a	(12)
RL (28)	1,426	c	776	b	(53)	761	a	(51)	568	c	(40)	96	e	(7)	44	c	(3)
GL (17)	2,990	ab	1,394	a	(47)	1,506	a	(51)	1,149	b	(38)	212	cd	(7)	62	c	(2)
Yc (16)	1,507	c	636	b	(41)	789	a	(50)	527	c	(36)	122	de	(8)	48	c	(5)
Ym (23)	2,352	bc	1,069	ab	(43)	1,424	a	(58)	612	c	(28)	237	bc	(11)	59	c	(3)
Yf (24)	2,279	bc	767	b	(34)	1,009	a	(38)	845	bc	(37)	324	ab	(19)	104	bc	(5)
BF (15)	1,478	c	880	ab	(60)	882	a	(60)	353	c	(23)	148	ce	(10)	34	c	(3)

BLn: Brown Lowland soils; BLh: Brown Lowland soils with humic layer; RL: Regosolic Lowland soils; GL: Gray Lowland soils; Yc: Yellow soils coarse texture; Ym: Yellow soils medium texture; Yf: Yellow soils fine texture; BF: Brown Forest soils. AA-P, NH₄F-P and NaOH-P were extracted sequentially by acetic acid, NH₄F and NaOH, respectively (Sekiya 1983). TP indicates total P content. Different letters correspond to significant differences (p < 0.05) among the soil groups.

Table 4. Correlation coefficients between the amounts of P determined by chemical extraction and selected soil properties

	Truog-P		Sequential P fractionation						TP
			AA-P		NH4F-P		NaOH-P
pH	0.368	**	0.398	**	-0.277	*	-0.131		0.089
Total C	0.417	**	0.471	**	0.413	**	0.417	**	0.612	**
ExCa	0.473	**	0.412	**	0.205		0.445	**	0.442	**
Alo	0.041		-0.020		0.568	**	0.628	**	0.411	**
Feo	0.244		0.160		0.762	**	0.436	**	0.546	**
Alo + 1/2Feo	0.127		0.066		0.714	**	0.630	**	0.533	**
Ald	0.073		0.081		0.331	*	0.797	**	0.361	**
Fed	0.051		0.061		0.094		0.706	**	0.183
Clay	-0.095		-0.019		-0.084		0.650	**	0.684	**

* and ** indicates statistical significance at the level of p<0.01 and p<0.001, respectively (Spearman’s rank correlation coefficient test). AA-P, NH₄F-P and NaOH-P were extracted sequentially by acetic acid, NH₄F and NaOH, respectively (Sekiya 1983). ExCa: exchangeable Ca; Al_o and Fe_o: Al and Fe extracted by acid ammonium oxalate, respectively; Al_d and Fe_d: Al and Fe extracted by dithionite-citrate bicarbonate, respectively; TP, total phosphorus.

Figure 2. Phosphorus K-edge XANES spectra for standard materials. Ca-P, Al-P and Fe-P indicate P associated with Ca, Al and Fe, respectively

Figure 3. Phosphorus K-edge XANES spectra of 14 soil samples. Right panels represent the close-up views of post-edge region and white-line peak to compare spectra features of P associated with Ca (Ca-P) and Al (Al-P), respectively. Ca-P, Al-P and Fe-P indicate P associated with Ca, Al and Fe, respectively. BLn: Brown Lowland soils; BLh: Brown Lowland soils with humic layer; RL: Regosolic Lowland soils; GL: Gray Lowland soils; Yc: Yellow soils coarse texture; Ym: Yellow soils medium texture; Yf: Yellow soils fine texture; BF: Brown Forest soils

Table 5. Phosphorus K-edge XANES spectra linear combination fitting results showing the relative proportion of P standards giving the best fit to the spectra from the soil samples

Soil	R	XANES (%)					Chemical extraction (%)				TP	pH	ExCa	Alo	Feo	Clay
		Ca-P		Al-P		Fe-P	Truog	AA	NH4F	NaOH
	(R)	(CP)	(HAP)	(Gib)	(Kao)	(Fer)								g kg^−1
BLn	0.001	8		52		40	33	38	44	5	2.3	7.0	60	2.7	2.9	119
BLh	0.002	13		47		40	19	22	62	4	7.9	5.9	131	8.7	4.8	208
RL	0.002	49		–		51	43	68	28	4	2.8	6.3	61	0.6	2.0	76
	(0.001)	(36)	(10)	–	–	(54)
GL	0.002	49		6		45	47	56	35	5	4.4	6.2	117	1.8	4.3	91
Yc1	0.008	56		–		44	66	78	15	4	2.4	7.2	55	0.6	0.5	108
	(0.002)	(47)	(28)	–	–	(25)
Yc2	0.003	58		–		42	46	51	34	10	1.2	5.5	38	0.5	0.9	70
Yc3	0.003	50		–		50	54	55	30	10	1.2	6.1	53	0.5	1.0	70
Yc4	0.002	38		–		62	34	41	47	6	1.5	5.7	36	0.6	1.4	70
Ym1	0.007	25		10		65	43	51	37	10	1.4	6.3	63	1.3	0.8	178
Ym2	0.002	71		9		20	60	56	23	11	3.2	7.0	130	1.6	2.3	198
Yf1	0.008	22		78		–	28	26	36	36	1.7	6.3	63	2.0	1.0	451
	(0.004)	(12)	–	(69)	(19)	–
Yf2	0.008	26		74		–	22	20	36	24	0.8	5.4	38	0.9	1.2	315
	(0.006)	(30)	–	(48)	(22)	–
Yf3	0.006	83		17		–	29	71	21	5	11.8	6.9	235	2.8	3.0	437
	(0.003)	(31)	(53)	(16)	–	–
BF	0.013	65		–		35	67	73	19	5	1.7	6.8	58	0.8	0.6	168

Linear combination fitting (LCF) using CaHPO₄ as Ca-P, PO₄ adsorbed on gibbsite as Al-P and P adsorbed on ferrihydrite as Fe-P. Brackets indicates the LCF result reanalyzed by assuming the presence of Hydroxyapatite (HAP) and PO₄ on kaolinite (Kao); CaHPO₄·2H₂O (CP); PO₄ on gibbsite (Gib); PO₄ on ferrihydrite (Fer). R indicates the normalized root-square difference between the data and the fit. Truog, AA, NH₄F and NaOH indicated P extracted by Truog method, acetic acid, NH₄F and NaOH, respectively. TP: total P (g kg^-1); ExCa: exchangeable Ca (mmol_ckg^-1); Al_o and Fe_o: Al and Fe extracted by acid ammonium oxalate, respectively. BLn: Brown Lowland soils; BLh: Brown Lowland soils with humic layer; RL: Regosolic Lowland soils; GL: Gray Lowland soils; Yc: Yellow soils coarse texture; Ym: Yellow soils medium texture; Yf: Yellow soils fine texture; BF: Brown Forest soils.

Figure 4. Phosphorus K-edge XANES spectra of the best results of linear combination fitting with standard spectra. (a)(b): Linear combination fitting (LCF) using CaHPO₄ as Ca-P, PO₄ adsorbed on gibbsite as Al-P and P adsorbed on ferrihydrite as Fe-P; (c): LCF result by adding HAP (hydroxyapatite) to the standards used in (a); (d): LCF result by adding Kao (PO₄ on kaolinite) to the standards used in (b). Yc: Yellow soils coarse texture; Yf: Yellow soils fine texture

Figure 5. Relationships among the proportions of different P species determined by P K-edge XANES linear combination fitting analysis and chemical fractionation. (a) Truog-P; (b) AA-P; and (c) NH₄F-P. Ca-P, Al-P and Fe-P indicate the proportion of CaHPO₄, P adsorbed on gibbsite and ferrihydrite calculated by linear combination fitting (LCF), respectively. CP and HAP indicate the proportion of P in CaHPO₄ and hydroxyapatite reanalyzed by assuming the presence of hydroxyapatite

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