Title: Effect of dietary protein concentration on ammonia and greenhouse gas emitting potential of dairy manure Authors
Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 14, 2011
Publication Date: April 1, 2012
Citation: Lee, C., Hristov, A.N., Dell, C.J., Feyereisen, G.W., Kaye, J., Beegle, D. 2012. Effect of dietary protein concentration on ammonia and greenhouse gas emitting potential of dairy manure. Journal of Dairy Science. 95:1930-1941. Interpretive Summary: The emissions of ammonia during manure storage and after its application to soil is both a source of air pollution (contributes to smog formation) and is a major pathway for the loss of plant-available nitrogen. Additionally, greenhouse gas emissions (nitrous oxide, methane, and carbon dioxide) are also associated with manure handling and land application. Previous research has indicated that feeding excess crude protein can reduce the efficiency of nitrogen utilization by the animals, producing manure that has a higher nitrogen content with a greater potential for conversion of manure nitrogen to ammonia and possibly nitrous oxide. The current study was conducted to test the effect of dietary crude protein concentration on ammonia and greenhouse gas emissions from dairy manure. Manure was obtained by feeding dairy cattle either a high (16.3%) or low (13.5%) crude protein diet. The manure from the high crude protein diet had greater ammonium- and urea-nitrogen content (4.4 vs. 2.8% and 51.4 vs. 30.5%, respectively). During simulated manure storage, ammonia emission rate was 47% lower with the low crude protein manure. Additionally, nitrous oxide emissions were not detected during the measurement period from either type of manure, and carbon dioxide and methane emissions were similar with the two manures. When the two types of manures were applied to the surface of large soil cores, ammonia emissions were 33% lower with the low crude protein manure. However, methane and carbon dioxide emissions were somewhat greater with low crude protein manure. These larger greenhouse gas emissions appear to result from the greater application rate of the low crude protein manure due to its lower total nitrogen content and the need to apply more manure to meet the crop nitrogen requirement. These results demonstrate that ammonia emissions from manure can be substantially reduced by managing crude protein content of dairy feed.
Technical Abstract: The objective of these experiments was to investigate the effect of dietary crude protein concentration on ammonia and greenhouse gas (GHG; nitrous oxide, methane, and carbon dioxide) emissions from dairy cow manure in simulated storage (Exp. 1) and from manure amended soil (Exp. 2). Manure was prepared from lactating Holstein cows fed diets with 16.3% (DM basis; HighCP) or 13.5% CP (LowCP). HighCP manure had higher N content and proportion of ammonia- and urea-N in total manure N (DM basis: 4.4 vs. 2.8% and 51.4 vs. 30.5%, respectively). In Exp. 1, ammonia emission rate was greater for HighCP compared with LowCP manure (5.52 vs. 2.93 mg per square meter per min, respectively). The cumulative end-point (122 h) ammonia emission was reduced by 47% for LowCP compared with HighCP manure. The emission rates and cumulative emissions of GHG were not different between HighCP and LowCP manure. In Exp. 2, LowCP and HighCP manures were applied to lysimeters (61 × 61 × 61cm; Hagerstown 35 silt loam; fine, mixed, mesic Typic Hapludalfs) at similar N application rates. Ammonia emission rate (1.53 vs. 1.03 mg per square meter per min) and the areas under the emission rate curves were greater for lysimeters amended with HighCP than with LowCP manure. The cumulative end-point (100 h) ammonia emission was also greater for HighCP compared with LowCP manure. The average methane and carbon dioxide emission rates were greater for lysimeters amended with LowCP compared with HighCP manure. The cumulative end-point methane emission, however, was not different between treatments, while the cumulative carbon dioxide emission tended to be greater for LowCP compared with HighCP manure. Nitrous oxide emissions were low in this experiment and did not differ between treatments. In conclusion, manure from dairy cows fed LowCP diet significantly decreased ammonia emission in simulated storage conditions and from manure-amended soil, compared with manure from cows fed HighCP diet. The LowCP manure increased soil methane and carbon dioxide emission rates due to a larger mass of manure added to meet plant N requirements compared with HighCP manure.