Analysis of Ammonium-Nitrogen in Liquid Manure Samples by Dumas Combustion Method

Increased demand for organic alternatives to soil amendment necessitates improved nitrogen (N) determination, including ammonium (NH4+), which is a readily available nitrogen source in manure. Current methods of NH4+ quantification include Kjeldahl distillation, ion selective electrode (ISE), and colorimetry. The Kjeldahl method has remained the most accurate and reproducible for the analysis of liquid manure agricultural samples, as the latter methods are limited by cation and turbidity interferences. The Kjeldahl method is tedious, waste-generating, presents safety concerns, and only detects exchangeable NH4+ nitrogen; therefore, safer, more efficient, and informative alternatives are needed.

To create a rapid, accurate, and safer technique that does not generate chemical waste, while providing crucial quantification.

Three AOAC Methods (973.49 Kjeldahl -N, 992.15 Dumas total nitrogen ([TN]), and 978.02 Kjeldahl total nitrogen [TKN]) were utilized to demonstrate the validity of an alternate technique developed in our laboratory for the detection of -N by Dumas combustion. Known N standards were tested to confirm equivalent detection across methods in this comparative study.

Liquid manure samples were analyzed for TN and NH4+ content using the standard methods and the Dumas-based technique, and quantifications were compared. Values were significantly similar between methods, verifying the comparability and effectiveness of the Kjeldahl and alternative Dumas-based techniques.

The technique of NH4+ determination by Dumas combustion provides equivalent quantifications to AOAC Methods. This technique is faster and as accurate as the standard Kjeldahl method, without chemical waste or significant safety hazards. The technique is applicable to high-throughput requirements and can provide detection of total nitrogen, NH4+, carbon, and sulfur, as an advantage over the Kjeldahl method.

The technique of NH4+ quantification described herein is safer, as accurate, and more efficient than the standard Kjeldahl method, allowing high throughput. Additionally, combustion analyzers can be fitted to detect sulfur and carbon, allowing simultaneous macronutrient detection.