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Table 2 Depth resolved phosphorus (P) speciation (% proportion of total P) of three long-term P fertilization sites (P-fertilized and non-P-fertilized (control), as obtained by linear combination fitting (LCF) on averaged P K-edge XANES spectra

From: Subsoils—a sink for excess fertilizer P but a minor contribution to P plant nutrition: evidence from long-term fertilization trials

Site

Treatment

Depth (cm)

Ca-associated P

Al-associated P

Fe-associated P

Organic-associated P

R-factor

ACP

Hydroxyapatite

CaHPO4 × 2H2O

AlPO4

P sorbed on gibbsite

P sorbed on goethite

Phytic acid

Dahlem

Control

0–30

19 ± 1

   

4 ± 4

68 ± 2

7 ± 1

0.003103

30–50

2 ± 2

   

36 ± 0

58 ± 1

4 ± 2

0.010016

70–90

 

40

  

23

36

 

0.006228

Mineral + organic P

0–30

11 ± 9

7 ± 10

 

24 ± 6

26 ± 10

25 ± 19

8 ± 6

0.003642

30–50

6 ± 6

5 ± 5

 

27 ± 1

 

52 ± 1

10 ± 0

0.003893

70–90

34 ± 3

 

4 ± 6

 

13 ± 1

44 ± 0

3 ± 4

0.003781

Freising Dürnast

Control

0–30

20

  

15

 

44

21

0.002441

30–60

7

  

0

12

57

24

0.004938

60–90

11

  

21

 

49

19

0.003804

Mineral + organic P

0–30

21

  

9

 

52

19

0.002279

30–60

 

8

 

15

 

55

27

0.003750

60–90

   

11

 

73

15

0.003848

Bad Lauchstädt

Control

0–30

27

    

47

26

0.003704

30–60

52

   

21

 

27

0.004682

60–90

56

   

27

 

17

0.005963

Mineral + organic P

0–30

49

   

31

 

19

0.002447

30–60

43

   

13

20

25

0.003174

60–90

47

   

26

 

27

0.005464

  1. ACP amorphous calcium phosphate