Nitrogen-15 labeling and nitrogen transformation in silage maize-cattle manure system

¹⁵N tracer technique has been used in N cycling and utilization for livestock manure. The abundance and amount of ¹⁵N in different manure components and N forms affect whether ¹⁵N fate is consistent with all manure N. The purpose of this article is to better understand the characteristics of ¹⁵N transformation in silage maize-cattle manure system and distribution in cattle feces and urine by using ¹⁵N tracer technique. First, a sand culturing experiment was conducted by watering improved Hoagland nutrient solution with ¹⁵N labeled ammonium sulfate (AS, 60 atom% ¹⁵N) to cultivate ¹⁵N labeled maize (“Nongda-108”). Then, ¹⁵N labeled maize was mixed with unlabeled maize at a ratio of 55︰45, according to their amount of nitrogen, to get mixed ¹⁵N forage. Finally, a 2-years-old cattle starved for 2 days was fed on the mixed ¹⁵N forage for 4 days and starved 2 days again. During the 6 days, cattle feces and urine were collected and measured separately. The results showed that ¹⁵N abundance was 48.024% in labeled maize, 26.579% in mixed silages, and 8.044% in cattle manure. In addition, 26.3% of AS ¹⁵N was discovered in maize, 36.0% of silage ¹⁵N was discovered in cattle manure. In all the manure N collected, fecal N, urine N, fecal ammonium N and urine ammonium N accounted for 70.25%, 29.75%, 5.44% and 0.03%, their ¹⁵N abundance were 9.223%, 5.261%, 6.505% and 5.419%, respectively. In ¹⁵N labeled manure of cattle fed on ¹⁵N labeled silage in a short period, the abundance of ¹⁵N in cattle urine and feces, and in different N forms were different. The ¹⁵N abundance of urine was lower than that of feces, and ¹⁵N abundance of mineral and easy-mineralized nitrogen was lower than that of hardly mineralized nitrogen.