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Abstract.

Global awareness of nitrogen loss from livestock manure is driving research towards reducing ammonia emissions. The majority of manure ammonia is produced by the hydrolysis of urine urea by urease enzyme from fecal bacteria near the time of deposition. Over time, microbial activity produces additional ammonia through the metabolism of organic nitrogen in manure. An immediate and accurate field method would be a useful tool to quantify ammonia formation and loss. Standard colorimetric methods of measuring ammonia typically involve extensive sample preparation and costly equipment. Ammonium ion selective electrodes (AISEs) are a common portable tool used for water quality analysis but little literature exists for their use in manure solutions. Manure solutions contain much higher concentrations of ammonium and other ions than municipal wastewater, resulting in high ionic strength and other potential interferences in an AISE response. A method that corrects for these interferences would enable more rapid measurement of ammonium. Comparison with spectrophotometric lab analysis was used to determine the effect of sow urine on AISE response. Dilutions of sow urine with and without ammonium spikes were used to assess the effect of ionic strength and K:NH₄ ratios on AISE response. Results confirm that ionic strength exerts a suppressive effect while high interfering ion ratios increase the reading. Based on these results, future work may determine how to mitigate the effects of high ionic strength and interfering ion concentrations in manure solutions. This will allow the development of a methodology for determining ammonium concentrations in these solutions.