Doctor of Philosophy (PhD)


Plant, Environmental Management and Soil Sciences

Document Type



Calcareous soils make up some of the most productive agriculture lands in Louisiana. Due to their minimal occurrence little research has been done on these soils. Understanding phosphorus (P) chemistry is necessary for environmentally sound management of these soils. In this study, P speciation was investigated using several chemical fractionation procedures as well as x-ray absorption near-edge spectroscopy (XANES) coupled with principal component analysis (PCA) and least-squares linear combination fitting (LCF) on five calcareous Louisiana soils of different geological origins. Phosphorus sorption isotherm parameters were determined and their relationships with other properties were evaluated. In addition, Zinc (Zn) lability due to the interaction with P and other fertilizer nutrients was characterized and a fertilizer P and Zn response trial for corn on a calcareous Norwood silt loam soil was conducted. The results showed that these calcareous soils were dominated by Ca-P phases. All chemically defined sequential P fractions except HCl-P were significantly correlated with different Fe fractions especially amorphous Fe, indicating that Fe-oxides play an important role in P retention. A significant correlation was found between P speciation by XANES analysis and sequential P fractionation for total Ca-phosphates as well as total Fe-/Al-phosphates (R2 ≥ 0.81, P ≤ 0.0383). Further, an inclusion of the NaHCO3 extraction in chemical fractionation procedures caused a redistribution of Fe-/Al-P while Ca-P was unchanged. The evaluation on P and Zn interaction showed that the presence of PO43- decreased where as NH4+ increased Zn lability, suggesting that Zn and P fertilizer placement should be separated while the simultaneous application of Zn and ammonium-N amendments could improve plant Zn availability. The field experiment exhibited a P fertilizer response when Bray II soil test P was < 220 mg kg-1 while a Zn fertilizer response was dependent on P levels even when soil test Zn was very low by DTPA. It is concluded that P forms not only control P retention mechanisms for agronomic and environmental availability but also affect management of other nutrients in soils.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Jim Jian Wang