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


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{dagger} of the selected soil samples.

Sample
Soil
horizon
Soil
classification{ddagger}
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

{dagger} OM, organic matter content; M3Ca and M3P, Mehlich III–extractable calcium and phosphorus; Pt, soil total phosphorus determined after digestion with concentrated H2SO4 + H2O2 as in the last step of the fractionation; Alox and Feox, ammonium oxalate–extractable aluminum and iron; Fedc, dithionite + citrate–extractable iron.

{ddagger} TH, Typic Humaquepts; AH, Aeric Humaquepts.



Table 2. Sequential P fractionation{dagger} 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){ddagger} 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)

{dagger} Pi, inorganic phosphorus; Po, organic phosphorus; Pt, 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.

{ddagger} 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 ({chi}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
{dagger}
Total Ca
phosphate
{dagger}
_ % of total P ± standard error{ddagger} _
_ % 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

{dagger} 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.

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



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