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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
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