Evaluation of two methods for ammonia extraction and analysis in silage samples

Three experiments were carried out to evaluate two methods of ammonia extraction and analysis in corn silage samples. In the first experiment ammonia was extracted with a 2 M KCl and measured either by a phenol-hypochlorite or a microdifusion method. Ammonia content of samples analysed by microdifusion were significantly higher (97.9 versus 61.2 mg of NH3-N/100 g of dry matter) (P<0.05) than those obtained by phenol-hypochlorite method. In the second experiment, fluid extraction from silage samples by mechanical pressing followed by phenol-hypochlorite assay was compared to extraction with 2 M KCl followed by microdifusion analysis of ammonia. The last method also resulted in higher ammonia values in silages (110.3 versus 95.4 mg of NH3-N/100 g of dry matter) (P<0.05). In this experiment, the accuracy of methods was also evaluated. There were not differences between runs for any of them. A third experiment was carried out to evaluate ammonia recovery from tubes, which was near 1.0 in both methods. An additional experiment was conducted to evaluate if aerobic exposure could change pH values and ammonia content of silage samples. It was verified that pH increased linearly through a 24 h period (P<0.05), varying between 3.91 and 4.34, while the slope for ammonia contents was not different from zero. Although both, phenol-hypochlorite and microdifusion methods were similarly accurate, mechanical pressing extraction and phenol-hypochlorite determination is a more practical and specific method for ammonia analysis in silage samples. Parallel use of phenol-hypochlorite and microdifusion methods, however, allow to estimate the volatile amines content in silages. Ammonia is not lost from silages until 24 h after removal from the silo.