Phosphorus and nitrogen runoff losses from high moisture soils and quantification of phosphorus compounds using ion exchange chromatography

Christopher A Baxter, Purdue University

Abstract

Successful prediction of phosphorus (P) and Nitrogen (N) losses from soils requires a thorough understanding of factors affecting those losses and accurate analytical methods for measuring nutrient fluxes. The first objective of the research described was to investigate the effects of soil moisture, time, and nutrient source on: (1) soil redox status, (2) runoff sediment, P, and N losses, and (3) soil P availability and distribution following reduction and reoxidation. Simulated runoff experiments were conducted on two Indiana soils maintained at saturated (SAT) and wet but not saturated (WET) conditions for up to 28 days. Soils maintained in the SAT condition consistently produced lower soil redox potentials, greater runoff volumes, greater sediment loads, and increased total and dissolved P in runoff compared to soils maintained under the WET condition. Increased sediment and total P losses from soil maintained under the SAT condition were attributed to decreased soil strength and decreased resistance to dispersion, while increases in dissolved P may be in part be attributed to release of P following reductive dissolution of Fe-oxides. Nitrification under the WET condition caused runoff NO 3 to increase in subsequent rainfall events, while under the SAT condition, runoff NO3 losses decreased due to denitrification. Lower soil P availability after incubation under the high moisture conditions was attributed to greater P sorption caused by increased amorphous iron oxide contents following reduction and reoxidation. The results of these experiments suggest that, under the moisture conditions evaluated, moisture had a greater impact on runoff P losses than a recently incorporated P addition. The second objective of this research was to describe methodology for quantifying organic P compounds in environmental samples. A rapid ion-exchange chromatography method was developed to simultaneously detect orthophosphate and several organic P compounds in environmental samples. The proposed method was able to simultaneously detect orthophosphate, glucose-6-phosphate (G6P), adenosine triphosphate (ATP), myo-inositol hexakis-phosphate (InsP6) and several lower inositol phosphate isomers in water and 0.05N HCl matrices. Calibration curves of combined standards containing orthophosphate, G6P, ATP, and InsP6 ranging from 5–500 ppm were achieved with r2 > 0.999. Advantages and limitations to the proposed method are discussed.

Degree

Ph.D.

Advisors

Joern, Purdue University.

Subject Area

Soil sciences|Environmental science|Agronomy

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