Soil iron fractionation and availability at selected landscape positions in a loessial gully region of northwestern China

Figures & data

Figure 1 The distribution of sampling sites across the watershed.

Table 1 The analysis of variance (anova) results of soil properties, diethylene thiamine pentacetic acid (DTPA)-Fe and Fe fractions at different landscape positions and soil depths

	pH	OM	CEC	DTPA-Fe	Ex-Fe	Carb-Fe	Ox-Fe	Om-Fe	Min-Fe
F
LP	20.9	9.29	41.9	34.3	10.0	18.0	14.4	27.2	13.5
SD	3.78	4.24	6.66	0.49	2.11	0.92	9.28	10.4	5.19
LP × SD	20.0	1.36	14.8	2.46	2.32	10.1	9.66	3.62	2.81
P
LP	<0.0001	0.0003	<0.0001	<0.0001	0.0002	<0.0001	<0.0001	<0.0001	<0.0001
SD	0.0366	0.0259	0.0048	0.6208	0.1428	0.4108	0.0010	0.0005	0.0130
LP × SD	<0.0001	0.2706	<0.0001	0.0525	0.0640	<0.0001	<0.0001	0.0101	0.0314
Carb-Fe, Carbonate bound Fe; CEC, Cation exchange capacity; Ex-Fe, Exchangeable Fe; LP, landscape position; Min-Fe, Minerals bound Fe; OM, organic matter; Om-Fe, Organic matter bound Fe; Ox-Fe, Oxides bound Fe; SD, soil depth.

Figure 2 Profile distribution of soil pH, organic matter, and cation exchange capacity at selected landscape positions.

Table 2 Fractional distribution of Fe in soils in Wangdonggou watershed

Soil layer	Ex-Fe (mg kg^−1)	Carb-Fe (mg kg^−1)	Ox-Fe (g kg^−1)	Om-Fe (mg kg^−1)	Min-Fe (g kg^−1)
0–20 cm
Mean (SE)	0.28 (0.14)	2.76 (0.77)	4.51 (1.25)	54.1 (17.6)	22.5 (2.41)
Range	0.08–0.65	1.78–4.43	1.26–6.22	14.4–84.5	19.1–26.8
CV	0.51	0.28	0.28	0.33	0.11
20–40 cm
Mean (SE)	0.27 (0.11)	2.57 (0.66)	4.67 (1.49)	50.6 (17.7)	21.6 (3.36)
Range	0.00–0.49	1.62–3.67	0.89–7.05	17.1–84.5	11.4–25.8
CV	0.41	0.26	0.32	0.35	0.16
40–60 cm
Mean (SE)	0.25 (0.07)	2.45 (0.70)	4.69 (1.21)	50.7 (19.2)	22.6 (2.85)
Range	0.08–0.33	1.38–3.67	1.89–7.03	17.1–102	18.6–29.1
CV	0.30	0.28	0.26	0.38	0.13
60–80 cm
Mean (SE)	0.23 (0.10)	2.35 (0.67)	4.62 (1.81)	49.5 (20.6)	22.2 (1.75)
Range	0.08–0.49	1.51–3.89	0.90–7.92	18.5–89.3	19.6–25.8
CV	0.45	0.29	0.39	0.42	0.08
Carb-Fe, Carbonate bound Fe; Ex-Fe, Exchangeable Fe; Min-Fe, Minerals bound Fe; Om-Fe, Organic matter bound Fe; Ox-Fe, Oxides bound Fe.

Figure 3 Profile distribution of iron fractions at selected landscape positions.

Table 3 Path coefficient and correlation coefficients of soil properties to diethylene thiamine pentacetic acid (DTPA)-Fe

	Direct path coefficients	Indirect path coefficients			r
		pH	CEC	OM
pH	−0.123		−0.075	0.031	−0.166
CEC	0.193	0.048		−0.003	0.237
OM	0.369	−0.010	−0.002		0.357
CEC, Cation exchange capacity; OM, organic matter; r, correlation coefficient; r 0.01 = 0.215, n = 141.

Table 4 Path coefficient and correlation coefficients of Fe fractions to diethylene thiamine pentacetic acid (DTPA)-Fe

Fraction	Direct path coefficients	Indirect path coefficients					r
		Ex-Fe	Carb-Fe	Ox-Fe	Om-Fe	Min-Fe
Exe-Fe	0.227		−0.021	0.120	−0.037	0.044	0.333
Carb-Fe	0.049	−0.097		−0.008	0.026	−0.007	−0.037
Ox-Fe	0.812	0.034	−0.001		−0.143	0.050	0.753
Om-Fe	−0.213	0.040	−0.006	0.544		−0.003	0.361
Min-Fe	−0.227	−0.044	0.002	−0.180	−0.003		−0.453
Carb-Fe, Carbonate bound Fe; Ex-Fe, Exchangeable Fe; Min-Fe, Minerals bound Fe; Om-Fe, Organic matter bound Fe; Ox-Fe, Oxides bound Fe; r, correlation coefficient; r 0.01 = 0.215, n = 141.

Figure 4 Factor plot of diethylene thiamine pentacetic acid (DTPA) extractable iron and iron fractions.