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