Table 3 Content and percentage of Hedley P fraction distribution with profile depth under arid agricultural soils and paddy soils
Land use | Profile depth | Resin-Pi | NaHCO3-Pi | NaHCO3-Po | NaOH-Pi | NaOH-Po | HCl-Pi | Residual P | |
|---|---|---|---|---|---|---|---|---|---|
(cm) | (mg kg−1) | ||||||||
Arid agricultural soils | 0–20 | 49.9 ± 40.0a**†| 239.4 ± 169.6a* | 81.7 ± 55.1a | 225.1 ± 90.6a | 146.1 ± 68.2a | 374.3 ± 267.1a** | 307.5 ± 128.9a | |
20–40 | 19.4 ± 17.6b | 131.1 ± 81.1b** | 69.0 ± 52.7a | 154.1 ± 67.5ab | 138.1 ± 48.3a | 211.0 ± 153.5a | 358.2 ± 70.5a | ||
40–60 | 13.9 ± 20.1bc | 89.9 ± 92.3bc | 63.0 ± 34.7a | 146.7 ± 102.0b | 73.4 ± 46.3b | 190.4 ± 258.3a | 292.7 ± 125.5a | ||
Paddy soils | 0–20 | 5.4 ± 2.8a** | 88.3 ± 33.9a* | 51.3 ± 16.4a | 210.7 ± 78.6a | 163.1 ± 53.4a | 120.5 ± 38.3a** | 310.0 ± 102.7a | |
20–40 | 4.0 ± 2.1a* | 45.3 ± 23.6bc** | 47.0 ± 20.5a | 122.9 ± 52.2ab | 127.6 ± 61.0a | 109.5 ± 66.6a | 327.4 ± 45.0a | ||
40–60 | 3.5 ± 1.1a | 38.6 ± 12.8c | 43.3 ± 11.5a | 101.0 ± 27.5b | 55.8 ± 9.1b | 90.4 ± 67.3a | 224.9 ± 37.3b | ||
Percentage of P (%) | |||||||||
 Arid agricultural soils | 0–20 | 3.1 ± 1.6 | 15.5 ± 4.9 | 5.7 ± 2.2 | 16.7 ± 5.5 | 12.2 ± 8.4 | 24.5 ± 9.1 | 22.2 ± 6.0 | |
20–40 | 1.6 ± 1.1 | 11.3 ± 4.6 | 6.0 ± 2.4 | 14.1 ± 4.0 | 13.7 ± 5.3 | 17.9 ± 8.6 | 35.4 ± 9.9 | ||
40–60 | 1.3 ± 1.2 | 9.0 ± 4.1 | 8.5 ± 3.3 | 16.5 ± 2.4 | 11.2 ± 6.9 | 16.6 ± 10.6 | 37.1 ± 10.0 | ||
Paddy soils | 0–20 | 0.6 ± 0.2 | 9.3 ± 1.7 | 5.4 ± 0.5 | 22.2 ± 3.3 | 17.3 ± 2.9 | 12.9 ± 2.6 | 32.5 ± 4.1 | |
20–40 | 0.5 ± 0.2 | 5.5 ± 1.9 | 6.1 ± 2.4 | 15.2 ± 3.6 | 16.0 ± 5.1 | 13.2 ± 6.7 | 43.7 ± 11.1 | ||
40–60 | 0.6 ± 0.1 | 6.8 ± 1.5 | 7.8 ± 1.4 | 18.0 ± 2.7 | 10.4 ± 2.6 | 15.0 ± 9.1 | 41.4 ± 9.6 | ||
Analysis of variance (P value) | |||||||||
 Land use |  < 0.001 |  < 0.001 | 0.024 | 0.145 | 0.790 | 0.003 | 0.220 | ||
 Profile depth | 0.020 | 0.006 | 0.571 | 0.001 |  < 0.001 | 0.174 | 0.035 | ||
 Land use × profile depth | 0.039 | 0.270 | 0.906 | 0.824 | 0.568 | 0.343 | 0.542 | ||