Date of Award

5-2006

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Plants, Soils, and Insects

Major Professor

Jaehoon Lee

Committee Members

Michael E. Essington, Daniel C. Yoder, H. Paul Denton, Ed Perfect

Abstract

Increasing concerns about contamination of soil and aquatic environments have emphasized the importance of information about the fate and transport of agricultural chemicals in soil. The objective of this research was to provide an improved understanding of the behavior of reactive chemicals including nitrate, phosphate, and antibiotics in soil through leaching and surface runoff in order to develop appropriate technologies that can prevent or minimize contamination of soil and water by agricultural activity. In a first experiment, a time domain reflectometry (TDR) method was tested for its ability to measure preferential flow of nitrate and phosphate in soil. Saturated miscible displacement experiments were conducted using three undisturbed soil cores and tracer solution containing chloride, phosphate, and nitrate. Predicted breakthrough curves (BTCs) obtained from the mobile-immobile model parameters fitted to the TDR data were comparable to the measured effluent nitrate BTCs. Phosphate BTCs distinctly differed from chloride and nitrate BTCs, thus the TDR method did not work for phosphate. The vertical TDR probe technique proved to be a practical method for a first approximation of nitrate preferential flow in soil. The second experiment used a localized compaction and doming (LCD) applicator that was developed to reduce nitrate leaching and increase nitrogen use efficiency. During a two-year period, sediment and nutrient losses from plots prepared using the LCD were compared to those prepared using conventional no-till broadcast (NTB) and no-till coulter injection (NTC). Concentrations of nitrogen and bromide in the soil profile were also determined to quantify anion movement. Total sediment loss for LCD was significantly greater than sediment loss for NTC and NTB. Masses of bromide, nitrate, phosphate, total nitrogen, and total phosphorus in runoff for LCD were significantly less than the corresponding masses for NTB and NTC in 2004. Residual concentration profile values implied that nitrate applied by the LCD applicator was transported more slowly through soil compared with the other methods. Therefore, the LCD method can reduce phosphorus loss in runoff, although on sloping fields it appears to result in more soil erosion. In the third and final experiment, the effects of soil properties on the fate and transport of chlortetracycline (CTC), tylosin (TYL), and sulfamethazine (SMT) were examined by conducting batch and column experiments. Sorption of CTC and TYL to montmorillonite and kaolinite generally decreased with increasing pH and ionic strength. Decreased retention of CTC and TYL to clays and soils was observed in the presence of Ca2+ compared with Na+. Greater SMT sorption was observed for surface soils having higher soil organic matter compared with subsurface soils, indicating that SMT mainly binds to soil organic matter in soils. Addition of dissolved organic carbon (DOC) derived from dairy manure resulted in decreased sorption and increased mobility of CTC and TYL, while increasing sorption of SMT. Changes in pH, ionic strength, DOC level, and background electrolyte cation type in soil solution caused by concomitant application of animal manure can influence fate and transport of agricultural antibiotics in soils. Therefore, failure to take the animal manure application effects into account can lead to conclusions that have little relevance to real situations.

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