Evaluating the effect of an anticoccidioidal drug on the nitrogen cycle in agricultural soils

Evaluating the effect of an anticoccidioidal drug on the nitrogen cycle in agricultural soils

Summary

The objective of this dissertation research is to fully assess the impact of Narasin on nitrogen dynamics at a field site near Milford, Delaware. Narasin is a USDA approved anticoccidiodal agent administered to poultry. Agricultural soils are exposed to Narsin when poultry litter is applied as a nitrogen fertilizer. Narasin has a relatively short half-life in soil, but may persist at concentrations in the pg·kg^-1 to ng·kg^-1 range. Because sustainable fertilizer practices are based on known parameters of soil nitrogen cycle variation, microbial inhibition or delayed activity caused by antibiotics may undermine the ability of modeling tools to make strong fertilizer management recommendations, leading to reduced fertilizer use efficiency and increased losses of pollutant N species, including N₂O and NO₃^–.

In the first four months of this project, I have used the grant funds primary to purchase supplies that will be used for a series of isotopically labeled incubation experiments. Due to some difficulties with instrument configuration, the onset of these experiments was delayed by approximately two months. Having since resolved these issues, I have completed the first two rounds of quality-control tests to ensure both mastery of the planned techniques and reliability of data. Results of the QC tests are pending; in the meantime I am setting up the first round of incubation experiments.

There are no data to report at this time.

Objectives/Performance Targets

The first objective, quantifying the impact of Narasin on soil nitrogen transformation rates, will be achieved by conducting a comprehensive series of soil incubation tests designed to simultaneously quantify the rate of mineralization, nitrification, denitrification, N₂O emissions, and accumulation of NO₃^–. The approach is fully described in the project proposal. Presently, the incubation tests are still in the preliminary phases, with full results anticipated in April to June of 2014.

The second objective is to develop and test a dose-response model for the rate of mineralization, nitrification, denitrification, N₂O emission, and potential NO₃^– leaching as a function of soil moisture and sulfadiazine concentration. Achieving this objective is dependent upon the successful completion of Objective 1 and therefore there are no accomplishments to report at present.

Accomplishments/Milestones

Work on this project began in August 2013. Composited soil samples were collected from the field site in August, sieved to 2mm, and the soil is currently being stored at 0°C. Method development for quantification of N₂O by GC-ECD was planned for the months of August and September. Due to some configuration difficulties with the required column, progress has been delayed and it is now projected that this phase will be complete by the end of January 2014. In the meantime, Exetainer vials have been obtained and construction of 60 incubation chambers is complete. Each incubation chamber is outfitted with two sampling ports that have been pressure-tested to ensure they are air-tight. Additionally, I conducted a set of quality control experiments that were not described in the project proposal. These are intended to ensure the consistency and quality of our laboratory methods and data and to quantify recovery of mineral N from soil extractions and diffusions. Analytical results from the QC tests are pending. As soon as the GC-ECD method is validated, the incubation experiments will begin. If the QC tests results have not yet been received, soil extraction and gross mineral N quantification will proceed as planned, but isotopic diffusions will be delayed until the methods and recovery have been properly validated. To prevent losses during the delay, the soil extracts will be stored frozen until they can be diffused.

Impacts and Contributions/Outcomes

In the early stages of this project, it is difficult to assess its impacts or contributions to agricultural sustainability. However, preliminary data suggests that a significant shift in microbial activity and resulting N-cycling may results from exposure to trace levels of Narasin in soils. Should this be confirmed, the implication is that real-time nutrient management tools may be less accurate when poultry litter containing antibiotics is used as a fertilizer supplement. Direct consequences may include lower nitrogen use efficiency, reduced crop yield, and/or higher non-point source nitrogen pollution (N₂O and NO₃^–). If the planned dose-response model can accurately predict the response of soil microbial communities, appropriate adjustments can be made to offset these issues.

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