Date Full Report Received


Date Abstract Report Received



Primary Investigator:

Swine production and manure management and storage have been implicated as a major and increasing source of ammonia (NH3) emissions in North Carolina, with increasing environmental impact. Further, reports have stated that ammonium (NH4+) deposition, as measured by the National Atmospheric Deposition Program (NADP, a program established to determine long-term trends in NH4+ and other nutrient deposition in the United States), increased about 100% during periods overlapping the swine-production expansion period (1990-1996) in North Carolina, without considering deposition trends before or after the industry expansion or other changes that would have contributed to NH4+ depositions. As a result of this and other concerns, the North Carolina legislature enacted a moratorium on new swine farms in 1997. The swine industry questions this conjecture. Because of a lack of emissions data, the United States Environmental Protection Agency (USEPA) initiated studies across North Carolina to determine NH3 emissions from livestock operations under a USEPA Air Consent Agreement with the livestock industries. These studies were undertaken from 2007 to 2009, as a National Air Emissions Monitoring Study (NAEMS) funded by participating producers. These NAEMS studies estimated that swine NH3 emissions were 1.5 times larger from finisher and 18.3 times larger from sow production systems over what had been measured by a USDA study 10 years prior. The NAEMS authors suggested their increased estimates were likely caused by different measurement approaches and climate conditions but ignored other factors that affect emissions. The swine industry challenges the accuracy of the reported increase in emissions from swine farms since over this period the industry made numerous changes to improve feed efficiency which should have reduced emissions.

This study was initiated to establish how long-term enhancements in animal management have affected nutrient loading in lagoons. Regular lagoon sampling for chemical analysis has been required for lagoon permitting in North Carolina and the data from swine facilities have been archived for about 20 years. To evaluate the representativeness of the archived data, simultaneous lagoon sampling by farm employees and by the authors were performed to compare source and magnitude of sampling, analytical technique, and potential sample spatial variability. The simultaneous sampling and analysis showed no statistical difference between farm employee- and researcher-collected data, assuring the archived data’s usefulness in estimating trends in NH3 emissions, based on lagoon’s nutrient contents and climatic conditions. Archived results from samples taken on 159 primary waste-processing lagoons along with 23 secondary lagoons (not all farms had secondary lagoons), and representing about 106,000 laboratory analyses, were used for analysis.

Nutrient content trends in finisher primary lagoons measured excreted nutrient concentration reductions [total Kjeldahl nitrogen (TKN), phosphorous (P), potassium (K), and zinc (Zn)] ranging from 35% to 78% in the primary lagoons, with the exception of copper (Cu) which increased by 41%. All primary lagoon nutrient trends for sow farms, including Cu, also declined ranging from 17% to 68%. Nutrients in all secondary lagoons similarly declined, ranging from 27% to 95% decrease as the industry implemented swine management improvements. The trends in primary lagoon pH for finisher and sow farms showed decreases of 0.10 and 0.02 units, respectively, and 0.02 units for both types of farms’ secondary lagoons. The lagoon N and pH data, along with regional climate data plus process and empirical NH3 volatilization models, were used to calculate the changes in relative NH3 emissions over time and to examine the NH3 emissions’ relationship to improved swine production and management practices. Because of reduced N and decreased pH in the lagoons, the USDA process model for NH3 emissions showed trend decreases since 2001 of 47% and 22% from finishers’ and sows’ primary lagoons, respectively, and 49% and 50% from finishers’ and sows’ secondary lagoons, respectively. Additional statistical and empirical models estimated reductions in NH3 emissions ranging from 11% to 54%, based on the same archived data from all farms’ primary and secondary lagoons.

From 1979 through 2017, the period in which NH4+ deposition data is available, the swine population in North Carolina had three time-periods with very different but approximately linear growth rates: pre-1989 (pre-expansion period), 1990 through 1996 (expansion period), and 1997 through 2017 (post-expansion moratorium period). Human population growth in North Carolina during those three time periods was also approximately linear, with growth rates of 75,000 persons yr-1 pre-1989 and about 135,000 persons yr-1 during and after the swine-expansion periods. It might be expected that when the average yearly change in swine production increased from 44,000 swine yr-1 to 1,132,000 swine yr-1 in 1990 and then after 1996 (the moratorium period) down by a loss of 47,000 swine yr-1, there would be dramatic changes in deposition growth; but, this was not observed either statistically or graphically. Overall (1979 through 2017), NH4+ deposition at both rural and urban monitoring sites showed statistically significant linear increases (i.e. deposition approximately increased at a constant rate over time). However, when each separate time period was tested for a linear relationship (correlation), the calculated probabilities (p-values) were too large (p =0.18, p = 0.11 and p = 0.06 respectively) to claim a significant linear relationship between deposition and time. Since more data values would possibly allow for significant correlations, both monthly and weekly data were also evaluated. While the long-term trends had low calculated probabilities (p < 0.001), separate period linear relationships were not consistent, with the slopes changing with each data set and time period. However, because of variability in the data, a significant change in deposition during the period of rapid industry expansion cannot be claimed or disproven nor to what might have been the magnitude of possible changes for the pre- and post-expansion periods.

It is noteworthy that a visual inspection of the data shows lack of noticeable change in deposition growth after the expansion period. If swine population was the primary driving force for the increase in deposition during the period of rapid industry expansion, then after the moratorium the decrease in swine population combined with improved swine feed efficiency (-8%) and daily gain (+22%) would have resulted in a slowed growth of deposition in the years post-1996, but this was not observed. And, during this post-expansion period, fecal N and P were reduced by 34% and 62%, respectively. The increase in NH4+ deposition during the post-expansion period is an indicator that non-swine factors affect NH4+ deposition in both rural and urban North Carolina.

In summary, an analysis of archived lagoon nutrient data collected for the swine industry permitting process indicated a significant reduction in the industry’s NH3 emissions’ footprint, as well as other nutrients, since initiation of lagoon sampling began in 2001. These data confirm that industry management and production improvements have been effective in reducing elemental excretion. Analysis of NADP data also indicated that an increase in rural and urban NH4+ deposition over the last 40 years, which has been attributed to increasing swine population and other agricultural production, is neither accurate nor complete and that human population and its associated NH3 emissions must be investigated as a significant factor.

Contact Information:
L.A. Harper, Harper Consulting, P.O. Box 772, Watkinsville, GA 30677; 706-769-9770; lowry.harper.pe@gmail.com. (Agricultural physics/engineering)
K.H. Weaver, Southern Utah University, 315 W. Center St., SC 309, Cedar City, UT 84720;
435-865-8047; weaver@suu.edu. (Analytical/physical chemistry)
S.M. Duffin, Southern Utah University, 325 W. Univ. Blvd., Cedar City, UT 84720; 435-865-8173; duffin@suu.edu. (Mathematics/statistics)
M.T. Coffey, Smithfield Hog Production Division, P.O. Box 759, Rose Hill, NC 28458; tcoffey@smithfield.com. (Animal nutrition)
T.K. Flesch, University of Alberta, CCIS 270, Edmonton, AL T6G 2E3; 780-492-5406; tk.flesch@gmail.com. (Microclimatology)