| Abstract |
Phosphorus (P) speciation determines its bioavailability, mobility, and environmental risk in soils. Farmland soils around mining areas are worldwide distributed, yet the P speciation in such soils remains poorly understood. In this study, we determined the P speciation in the farmland soils and soil aggregates around mining areas from China and evaluated their relationship with soil pH and Fe/Al fractions using chemical extraction, P K-edge X-ray absorption near-edge (XANES) spectroscopy, and correlation analysis. Chemical extraction revealed that soil P was dominated by inorganic P (Pi) (68.0 – 82.5%) largely associated with pedogenic Fe/Al oxides (43.4% – 94.8%). The P was mainly adsorbed and occluded by Fe/Al oxides in acidic soils, while predominantly existed as Ca-P and occluded species in alkaline soils. The presence of heavy metals appeared to have no significant effect on P speciation in these soils. Compared with the macroaggregates, the available P, total P, and their ratio all increased dramatically in the soil colloids (< 0.002 mm) due to the accumulation of Fe/Al oxides. The XANES analysis indicated that the P speciation in the acidic soils and soil aggregates was dominated by Fe-P, followed by Al-P, and little Ca-P; in contrast, the proportions of Ca-P increased but Fe-P decreased in the alkaline soils and soil aggregates. Compared with the macroaggregates, the proportions of Fe-P increased while Ca-P decreased in the soil colloids. Correlation analysis indicated that amorphous Al and isomorphic substitution Al played critical roles in P immobilization by pedogenic Fe/Al oxides. These new insights into the P speciation are essential for environmental risk assessment and efficient utilization of P in the farmland soils. |
, Chunhao Gu 
