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Table 5 Concentrations and percentages of inorganic P compounds in extracts of whole soil or residues, determined by solution P-NMR spectroscopy

From: Characterizing the phosphorus forms extracted from soil by the Mehlich III soil test

 

Extractant

 

AR-control

AR-N

AR-PL

AR-PL-alum

SK

PEI

Till Ref

MRP

Mehlich III

Soil

31 (47)

59 (67)

378 (100)

369 (59)

60 (61)

211 (86)

29 (97)

Orthophosphate

Mehlich III

Soil

31 (49)

50 (59)

332 (87)

338 (50)

69 (70)

213 (87)

22 (72)

 

NaOH-EDTA

Residue

149 (59)

157 (51)

426 (71)

497 (45)

102 (50)

275 (69)

102 (31)

 

NaOH-EDTA

Soil

118 (42)

139 (43)

562 (75)

663 (56)

155 (46)

573 (76)

207 (58)

 

NaOH-EDTA

Difference

− 31 (− 17)

− 17 (− 9)

136 (4)

167 (11)

54 (− 4)

298 (6)

105 (26)

Pyrophosphate

Mehlich III

Soil

0 (0)

0 (0)

1 (0)

1 (0)

0 (0)

0 (0)

0 (0)

 

NaOH-EDTA

Residue

3 (1)

10 (3)

6 (1)

8 (1)

6 (3)

6 (2)

6 (2)

 

NaOH-EDTA

Soil

12 (4)

7 (2)

12 (2)

20 (2)

3 (1)

5 (1)

8 (2)

Polyphosphate

Mehlich III

Soil

1 (2)

1 (1)

2 (1)

4 (1)

2 (2)

2 (1)

1 (2)

 

NaOH-EDTA

Residue

2 (1)

5 (2)

2 (0)

8 (1)

4 (2)

2 (1)

4 (1)

 

NaOH-EDTA

Soil

8 (3)

5 (1)

14 (2)

12 (1)

5 (1)

6 (1)

5 (1)

Total inorganic P

Mehlich III

Soil

32 (49)

50 (60)

334 (87)

343 (51)

71 (72)

215 (88)

22 (74)

 

NaOH-EDTA

Residue

155 (61)

172 (56)

435 (72)

512 (47)

112 (55)

284 (72)

112 (34)

 

NaOH-EDTA

Soil

138 (49)

150 (46)

588 (78)

695 (59)

163 (48)

584 (77)

221 (61)

 

NaOH-EDTA

Difference

− 16 (− 12)

− 21 (− 10)

154 (6)

183 (13)

51 (7)

300 (5)

109 (27)

  1. Concentrations are given in mg kg−1 soil (% of total P in each extract). MRP is molybdate-reactive P, determined colorimetrically in the Mehlich III extracts. Residue is the residual soil after Mehlich III extraction. Total inorganic P is the sum of orthophosphate, pyrophosphate and polyphosphate. Difference is the difference in between the NaOH-EDTA extracts of whole soils and the NaOH-EDTA extracts of the residue after Mehlich III extraction