X-ray absorption near-edge structure (XANES) spectroscopy was used in conjunction with sequential …

• Abstract
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• Materials and Methods
• Results
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• References
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Biology Articles » Agriculture » Speciation of Phosphorus in Phosphorus-Enriched Agricultural Soils Using X-Ray Absorption Near-Edge Structure Spectroscopy and Chemical Fractionation » Tables

Tables

- Speciation of Phosphorus in Phosphorus-Enriched Agricultural Soils Using X-Ray Absorption Near-Edge Structure Spectroscopy and Chemical Fractionation

Table 1. Basic properties of the selected soil samples.

Sample Soil horizon Soil classification Source of P Sand Clay OM pH (water) M3Ca M3P Pt Alox Feox Feox/Fedc _ g kg-1 _ _ mg kg-1 _ mmol kg-1 sb2.1  Ap TH mineral 280 192 82 5.8 1116 38 2076 673 116 0.81 Ma2  Ap AH manure 800 50 66 6.2 1374 103 1189 282 117 0.81 PV2  Ap AH mineral 77 750 40 7.4 3112 63 1223 76 122 0.72 Ma3  Bg AH manure 620 30 28 5.5 316 10 814 182 92 0.61 AI2  Bg TH mineral 438 254 3 7.6 1519 4 884 29 58 0.23

OM, organic matter content; M3Ca and M3P, Mehlich III–extractable calcium and phosphorus; P_t, soil total phosphorus determined after digestion with concentrated H₂SO₄ + H₂O₂ as in the last step of the fractionation; Al_ox and Fe_ox, ammonium oxalate–extractable aluminum and iron; Fe_dc, dithionite + citrate–extractable iron.

TH, Typic Humaquepts; AH, Aeric Humaquepts.

Table 2. Sequential P fractionation of the soil samples ± standard deviations.

NaHCO3 NaOH Sample Resin P Pi Po Pt Pi Po Pt HCl H2SO4 _ mg kg-1 _ sb2.1-A 98 ± 7 (5) 127 ± 3 (6) 100 ± 6 (5) 227 ± 9 (11) 743 ± 6 (34) 456 ± 43 (21) 1199 ± 46 (55) 434 ± 18 (20) 200 ± 39 (9) Ma2-A 77 ± 4 (5) 107 ± 6 (8) 76 ± 12 (5) 183 ± 18 (13) 427 ± 28 (30) 194 ± 29 (14) 621 ± 50 (44) 374 ± 32 (27) 147 ± 23 (11) PV2-A 86 ± 1 (7) 34 ± 3 (3) 48 ± 5 (4) 82 ± 6 (7) 84 ± 5 (7) 154 ± 10 (13) 238 ± 13 (20) 476 ± 4 (40) 304 ± 43 (26) Ma3-B 18 ± 10 (2) 15 ± 1 (2) 47 ± 6 (6) 62 ± 7 (8) 82 ± 3 (10) 133 ± 13 (17) 215 ± 16 (27) 401 ± 30 (50) 102 ± 12 (13) AI2-B 24 ± 4 (3) 5 ± 1 (1) 19 ± 2 (2) 23 ± 2 (3) 10 ± 0 (1) 19 ± 4 (3) 29 ± 4 (4) 577 ± 6 (71) 155 ± 17 (19)

P_i, inorganic phosphorus; P_o, organic phosphorus; P_t, total phosphorus; resin P, the most available inorganic phosphorus; NaHCO₃–P, labile phosphorus sorbed on the soil surface; NaOH-P, phosphorus chemisorbed to aluminum or iron; HCl-P, apatite-type minerals; H₂SO₄–P, chemically stable organic phosphorus and relatively insoluble inorganic phosphorus.

The numbers in parentheses are the percentage of each fraction relative to the sum of all fractions.

Table 3. Phosphorus K-XANES (X-ray absorption near-edge structure) fitting results showing the relative proportion (percentage, normalized to sum = 100) of each phosphate standard that yielded the best fit to the soil XANES data in linear combination fitting.

Sample Goodness of fit (2) Sum of fractions before normalization PO4 on ferrihydrite PO4 on goethite PO4 on Al hydroxide PO4 on alumina Noncrystalline FePO4 Hydroxyapatite Octacalcium phosphate Total PO4 on Fe- or Al-oxide Total Ca phosphate _ % of total P ± standard error _ _ % of total P _ sb2.1-A 0.15 1.32 54 ± 2 34 ± 3 12 ± 1 88 12 Ma2-A 0.06 0.95 60 ± 1 22 ± 2 18 ± 1 60 18 PV2-A (1) 0.16 0.91 23 ± 1 24 ± 2 53 ± 2 23 77 PV2-A (2) 0.17 0.91 27 ± 1 27 ± 2 46 ± 2 27 73 PV2-A mean 25 75 Ma3-B 0.12 0.88 44 ± 1 11 ± 1 45 ± 2 44 56 AI2-B (1) 0.05 0.66 17 ± 1 59 ± 3 24 ± 3 17 83 AI2-B (2) 0.05 0.68 15 ± 1 59 ± 2 26 ± 3 15 85 AI2-B (3) 0.05 0.68 18 ± 1 58 ± 2 24 ± 3 18 82 AI2-B (4) 0.05 0.71 16 ± 1 59 ± 2 25 ± 3 16 84 AI2-B mean 17 83

Total PO₄ on Fe- or Al-oxide is the sum of PO₄ adsorbed on ferrihydrite, goethite, Al hydroxide, or alumina. Total Ca phosphate is the sum of hydroxyapatite and octacalcium phosphate.

Percent of total P after normalization to sum = 100% ± computed standard errors for the linear coefficients.