The objective of this study was to
determine the effect of diet CP levels on nitrous
oxide (N2O), ammonia (NH3), and methane (CH4)
emissions from 1) cattle housed in confined settings
and 2) cattle manure following surface application to
incubated soils. Twelve 500-kg Holstein steers were
fed diets containing 10% CP (10CP) and 13% CP
(13CP). The experimental design was a 2 × 2 Latin
square conducted during two 20-d periods. Diets
were fed for 14 d before each measurement period
to allow for diet acclimation. Steers were housed
in environmentally controlled rooms allowing for
continuous emission measures of N2O, NH3, and
CH4. At the end of the second period, manure was
collected and surface applied to incubated soils to
verify potential NH3 and N2O emissions. To assess
emissions from incubated soils, 2 experiments were
set up with 3 replicates each: Exp. 1, in which soil
fertilization was based on manure mass (496 g of
manure), and Exp. 2, in which soil fertilization was
based on manure N content (targeted at 170 kg N/ha).
Manure emissions were monitored for 7 d. Steers fed
13CP diets had increased daily NH3 emissions when
compared to steers fed 10CP diets (32.36 vs. 11.82 ±
1.10 g NH3/d, respectively; P < 0.01). Daily N2O
emissions from steers fed 13CP and 10CP diets were
significantly different only during Period 1 (0.82 vs.
0.31 ± 0.24 g N2O/d; P = 0.04). Steers fed the 10CP
diet had greater N2O emissions per unit of N consumed
than steers fed the 13CP diet (9.73 vs. 4.26 ±
1.71 mg N2O/g N intake; P = 0.01). Diet CP levels
did not affect enteric CH4 production from steers. In
terms of soil emissions, different CP levels did not
affect NH3, N2O, or CH4 emissions when soil fertilization
was based on manure mass. However, NH3
emissions were reduced when manure from steers
fed the 10CP diet was applied to soil based on N
content. Ammonia emissions decreased during the
7-d incubation period. Conversely, N2O emissions
increased over the period. Our results indicated that
management of diet CP levels of confined finishing
steers mitigates NH3 emissions from steers but does
not affect enteric CH4. In addition, results suggested
that soil characteristics might be as important as
manure N content to generate NH3 and greenhouse
gases from soils receiving manure fertilization.