Thesis Title:
Identification and quantification of phosphorus species in dual bands applied to a model calcareous system using XANES and solid state NMR
Project Description:
Research Area:
Phosphorus speciation and ionic interaction between phosphates and salts added together with P fertilizer to a calcareous soil.
Rationale:
Phosphorus deficiency commonly limits crop production and it is further aggravated in calcareous soils. Precipitation reactions between P and exchangeable Ca (or Mg) is one of the common reasons for the disappearance of P in calcareous soils. In highly calcareous soils there is a series of sparingly soluble Ca and/or Mg minerals which are formed when soluble P fertilizers are added. If there is a way of modifying the ionic environment in the soil-P interaction zone which prevents the formation of insoluble P compounds and that in turn helps in improving P solubility. This makes the basic theoretical approach for the current study to improve the agronomic efficiency of added P. As the experimental approach, soil exchangeable complex is being modeled to characterize the precipitation reactions which involve the exchangeable Ca and Mg. This is achieved by using a model soil system composed of synthetic resin, sand and CaCO3 to mimic soil conditions without the influence of other organic and inorganic soil constituents. Here, the resin serves as the soil exchangeable complex.
Objective:
The main objective is to investigate the one dimensional downward diffusive transport, precipitation reactions and transformation products of the P fertilizer applied together with non phosphatic salts using the model calcareous soil system.
Proposed Methodology:
The exchangeable complex (resin) of the model system will be saturated with both Ca and Mg to represent the actual exchangeable complex with equal base saturation and Ca:Mg ratio to that of a real calcareous soil. The different salts of interest are the combinations of sulphates and carbonates of ammonium, magnesium and potassium. These salts will be added to the model soil system with mono potassium phosphates. A column study will be carried out together with incubation to investigate the depth and time effect on the P precipitation reactions. Conducting the same experiment with the real soil will enable us to clearly understand the precipitation reaction with exchangeable Ca/Mg. It will also enable to differentiate precipitation reactions from other soil reactions including surface adsorption.
Identification of different P compounds and their solubility is of paramount important to determine which salt performing best to enhance P availability in soil. This will be done by using X-ray absorption near edge structure spectroscopy (XANES) and solid-state nuclear magnetic resonance (NMR) spectroscopy. Both techniques are element specific, non destructive and do not require crystalline samples. The use of solid state 31P NMR together with XANES spectra provides an appropriate method to obtain detailed molecular characterization of inorganic P in soil samples. Specifically for real soil it will be advantageous because XANES is not affected by the presence of paramagnetic elements like NMR.
Research Contribution to Knowledge:
The overall scope of this study is to identify the best non phosphatic salt which is reacting to result the greatest amounts of soluble P in calcareous soil using XANES and NMR. It will enable us to come up with a more efficient formula for P fertilizer which will help to lower the high fertilizer application rates in agricultural lands. From fertilizer P management perspective, it will be advantageous in both economic and environmental aspects. Lowering P loads to the soil will ensure more favorable and sustainable environment to the man kind while serving the plants with its optimum P nutrient requirement. In addition the information on the P reaction products and their transformation reactions in a calcareous soil will provide a great knowledge base for further P fertilizer research.
Supervisor:
Expected Date of Completion:
January 2012
Previous Degrees:
M.Sc. Physical Land Resources (Major in Soil Science) University of Gent, Belgium (2007)
M.Sc. Environmental Soil Science, University of Peradeniya, Sri Lanka (2005)
B.Sc. Agriculture in University of Peradeniya, Sri Lanka (2004)
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