Difference of nitrogen contents determined by the combustion and Kjeldahl method in response to nitrate nitrogen in some feedstuffs

Two experiments were conducted to examine the difference of nitrogen contents determined by the combustion (Cm) and Kjeldahl (Km) method and its response to nitrate nitrogen in ruminant feedstuffs. In Experiment 1, 14 ruminant feedstuffs were determined for combustion nitrogen (Cn), Kjeldahl nitrogen (Kn) and nitrate nitrogen (NO 3 -N). Although NO 3 -N resulted in a difference between the Cm and Km, the correlation coeffi cient of the NO 3 -N content and the value of "Cn-Kn" was low (R 2 = 0.6341), suggesting other factors infl uencing the difference of N determination between the Cm and Km. In Experiment 2, recoveries of net NO 3 -N were determined using Chinese wild rye-grass (CWG), maize grain (MG) and soyabean meal (SBM) supplemented with sodium nitrate at the level of 5, 10, 15, 20, 25, 30, 35, 40 and 45% on DM basis, respectively. The results showed that different recoveries of NO 3 -N by Km rather than Cm would account for the difference of Cn and Kn in some ruminant feedstuffs.