GHG Effect of Ammonia Emission from Dairy Farms

Dairy farms in Abbotsford emit an estimated 638 tonnes of ammonia, resulting in an equivalent of 3777 tonnes CO2 equivalent GHG emission.

Increased concern about the pollution effects of ammonia emission from agriculture has led to considerable research since the mid-90s. Management of manure is important because 75% of the nitrogen fed to our cows ends up in the manure. Of that 75%, ammonia emission on large dairy farms in Abbotsford was estimated to be 42% of the total nitrogen excreted, or 48 kg N per cow per year, based on a nitrogen management model created in the early 1990s (Brisbin 1994). Significant ammonia losses occur in the barn following manure excretion, and during manure storage.

It appears that the 1994 estimate was very close to more recent estimates. Using a modelling approach, Sheppard et al. (2011) estimated ammonia emission losses to be 46 kg N per cow per year on dairy farms in southcoastal British Columbia.

The 1994 model assumed N excretion rates of 116 kg/dairy cow/year (Brisbin 1994). An estimated 15% of the excreted N was emitted as ammonia from the free stall barns, 10% during storage in manure pits, 5% following spreading if incorporated immediately, and 20% if not incorporated.

Based on this information, dairy farms in Abbotsford in 1991 excreted 1369 tonnes of N, of which 1069 tonnes went to manure storage, and 746 tonnes was available for the crop. Ammonia emissions were 177 tonnes from dairy cow housing, 26 tonnes from animal housing yards, 120 tonnes during storage and 246 tonnes following manure application to the fields.

More recent research allow us to provide better estimates of ammonia emissions from our dairy farms in Abbotsford. One obvious error in the 1994 model was that we estimated consistent ammonia emission rates during the year, whereas we now know that ammonia emission increases with increasing temperature.

Nitrogen Excretion Rates per Cow

The N excretion rate of 116 kg N per cow per year may not reflect changes in genetics and higher milk production per cow. Sheppard et al. (2011) provided a review of nitrogen excretion rates per cow per year. In their modelling of ammonia emissions, they used a nitrogen excretion rate of 160 kg N per cow per year using an average diet containing 15.9% crude protein. Nennich et al. (2005) also reviewed the literature and developed a model for N excretion by dairy cattle. They reported N excretion rates of 179 kg N per lactating cow per year when fed 25 kg dry matter per day with a protein content of 17.5%.

In British Columbia, Dinn et al. (1998) reported N excretion rates of 154 and128 kg N/cow per year from dairy cows fed TMR diets consisting of grass silage, corn silage and grain. Crude protein content of these diets were 18.3 and 16.7%, respectively. Groff and Wu (2005) measured manure N excretion rates of 176 to 208 kg N per cow per year with dairy cattle fed alfalfa/corn silage diets ranging from 15 to 18.75 % protein.

The 160 kg N per cow per year for lactating cows suggested by Sheppard et al. (2011) appears to be a realistic number to use for N excretion rates for dairy cattle.

Nitrogen Excretion from Dairy Cows in Abbotsford

Using the N excretion rates from Sheppard et al. (2011) for lactating dairy cows, dry dairy cows, dairy calves and dairy heifers, we can calculate the N excretion from the 13,886 dairy cows (average N excretion of 148 kg N/cow/year to account for lactating an non-lactating cows) and 6,377 replacement cattle (average N excretion of 35 kg N/animal/year) in Abbotsford (Census of Agriculture 2011).

The estimated N excretion from dairy cattle in Abbotsford is 2,282 tonnes of actual N per year in 2011, which is 66% or 913 tonnes higher than the estimates provided for 1991 (Brisbin 1994).

Ammonia Emission from Animal Housing

In the 1994 nutrient cycling model, 15% of the excreted nitrogen was lost as ammonia consistently throughout the year (Brisbin 1994). We now know that ammonia emission increases with increasing temperature. Rumburg et al. (2008) observed that ammonia emissions were seasonal and ranged from 10 kg NH3/day in the winter to over 80 kg NH3/day in the summer from 185 milking cows (20 to 160 kg N per cow per year).

In a report for the US EPA, Battye et al. (1994) estimated an emission rate of 40 kg NH3 per dairy cow per year. Hristov et al. (2011) summarized 27 research reports on ammonia emission from dairy barns. The overall average emission was 59 g N/cow/day, or 21.5 kg N per cow per year, or 14.5% of a total of 148 kg N excreted per cow per year. They noted that emissions ranged from 0.3 to 90 kg N per cow per year. They noted that ammonia losses from dairy manure are expected to be greater at higher ambient temperatures and wind speed, in open-lot facilities, in buildings allowing instantaneous mixing of uring and feces, and with higher protein diets. They measured a 25% loss of excreted N as ammonia from a free stall dairy barn over a one year period in Pennsylvania.

Hollman et al. (2008) measured N intake, milk and manure production in a free stall dairy barn that was flushed 4 times per day in Virgina during a one year period. The manure excretion rate was 170 kg N per cow during the year, with 67.5 or 39% of the manure N unaccounted for immediately after flushing.

In Washington state, Rumburg et al. (2008) concluded that 40 kg N/cow/year or 22% of the 180 kg N per cow per year excreted was volatilized as ammonia in a free stall dairy barn.

Paul et al. (1998) measured up to 38% loss of total nitrogen excreted by dairy cattle under simulated conditions of a barn floor during a 24 hour period at 25 C. The ammonia emission was directly correlated with ammonium concentration in the manure, and was also correlated with the protein intake by the dairy cows. It is important to note that there was no mixing or disturbance of manure during this period as would be found in a typical dairy barn with cattle movement.

Based on recent research, I conclude that ammonia emissions from dairy barns in Abbotsford are more likely to average 20 to 25% of the N excreted. Therefore, of the 2282 tonnes of N excreted by dairy cows in Abbotsford, assuming a 20% loss as ammonia, the total ammonia emission is 456 tonnes per year.

It would be interesting to see if there is any work on ammonia emission from free stall dairy barns where the manure solids are recycled for bedding. I would expect ammonia emissions to be significantly higher than barns that use sawdust for bedding.

Ammonia Emission During Storage and Following Application to the Field

The 1994 nitrogen management model suggested a 10% loss of total nitrogen during storage, a 5% loss following field application if incorporated immediately, or a 20% loss if not incorporated (Brisbin 1994). Given these estimates, the greatest losses of ammonia occur in the animal housing. Ammonia emission from manure storages in Abbotsford are estimated to be 182 tonnes per year compared with the 456 tonnes from animal housing. If we assume an average of the 5% and 20% losses following manure application, we have a total of 205 tonnes of ammonia emitted following field application.

It does not appear that these numbers would change significantly. What may change is the timing, because with larger manure storage tanks, more manure is being applied in the early spring. Bittman et al. (2010) measured the highest ammonia emission rates in the lower Fraser Valley during May, which coincides with the time that most manure is being applied to the land.

Ammonia Emission Contributes to Nitrous Oxide Emission

The Intergovernmental Panel for Climate Change guidelines recommended including ammonia emissions in greenhouse gas calculations. The estimated the indirect effect of NH3 emission on nitrous oxide production to 2% (IPCC 2006). Given the estimates of 456 tonnes per year of ammonia emission from animal housing, and 182 tonnes per year from storage and land application, and given that the carbon dioxide equivalent of nitrous oxide is 296 times, we have a total of 3777 tonnes of CO2 equivalent greenhouse gas emissions resulting from ammonia emissions in dairy barns. We can use this number later in estimates of greenhouse gas emissions from agriculture in Abbotsford.

References

Battye, R. W. Battye, C. Overcash and S. Fudge. 1994. Development and selection of ammonia emission factors. Final report for US EPA.

Bittman, S., J. Tait, D. Hunt, S. Sheppard, K. Chipperfield and Q. Zheng. 2010. Ammonia emission inventory for farms in the Lower Fraser Valley with detailed spatial and temporal resolution. 15th International Union of Air Pollution Prevention and Environmental Protection Associations’ World Clean Air Congress, Vancouver, BC Sept 2010. http://events.awma.org/IUAPPA/presentations/5D/a151.pdf

Brisbin, P.E. 1997. Agricultural Nutrient Management in the Lower Fraser Valley. DOE FRAP 1995-27. Environment Canada.

Dinn, N.E., J.A. Shelford and L.J. Fisher. 1998. Use of the Cornell Net Carbohydrate and Protein System and rumen protected lysine and methionine to reduce nitrogen excretion from lactating dairy cows. Journal of Dairy Science 81: 229-237.

Groff, E.B. and Z. Wu. 2005. Milk production and nitrogen excretion of dairy cows fed different amounts of protein and varying proportions of alfalfa and corn silage. Journal of Dairy Science 88: 3619-3632.

Hollman, M., K.F. Knowlton and M.D. Hanigan. 2008. Evaluation of solids, nitrogen, and phosphorus excretion models for lactating dairy cows. Journal of Dairy Science 91: 1245-1257.

Hristov, A.N., M. Hanigan, A. Cole, R. Todd, T.A. McAllister, P. Ndegwa and A. Rotz. 2011. Review: Ammonia emissions from dairy farms and beef feedlots. Canadian Journal of Animal Science 91: 1-35.

IPCC. 2006. 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Volume 4. Agriculture, Forestry and Other Land Use. Chapter 10. Emissions from Livestock and Manure Management. http://www.ipcc-nggip.iges.or.jp/public/2006gl/pdf/4_Volume4/V4_10_Ch10_Livestock.pdf

Nennich, T.D., J.H. Harrison, L.M. Van Wieringen, D. Meyer, A.J. Heinrichs, W.P. Weiss, N.R. St-Pierre, R.L. Kincaid, D.L. Davidson and E. Block. 2005. Prediction of manure and nutrient excretion from dairy cattle. Journal of Dairy Science 88: 3721-3733.

Paul, J.W., N.E. Dinn, T. Kannangara and L.J. Fisher. 1998. Protein content in dairy cattle diets affects ammonia losses and fertilizer nitrogen value. Journal of Environmental Quality 27: 528-534.

Rumburg, B., G.H. Mount, J. Filipy, B. Lamb, H. Westberg, D. Yone, R. Kincaid and K. Johnson. 2008. Measurement and modeling of atmospheric flux of ammonia from dairy milking cow housing. Atmospheric Environment 42: 3364-3379.

Sheppard, S.C., S. Bittman, M.L. Swift and J. Tait. 2011. Modelling monthly NH3 emissions from dairy in 12 Ecoregions of Canada. Canadian Journal of Animal Science 91: 649-661.