Large bore traveling gun and center pivot irrigation systems have been used to apply treated lagoon effluent, liquid animal manure, and untreated slurry from swine and dairy farms in many parts of the USA. The primary advantage of using irrigation equipment to spread manure on cropland are the lower costs for energy and labor, and the higher speed of application as compared to using a tractor-drawn spreader. The primary disadvantages are related to increases in odor release and the possibility of spraying manure on roads or another person’s property.
Ammonia-N loss from land application of manure is important because it is a loss of fertilizer nitrogen, and it is a source of air pollution. A previous study and several extension publications state that irrigation of animal manure increases ammonia-N loss by 10% to 25% (Chastain, 2019). As a result, the total ammonia-N loss was the sum of the ammonia-N lost while the manure traveled from the irrigation nozzle to the ground and the ammonia-N lost as the manure released ammonia-N after striking the ground.
The objective of this presentation is to summarize the results of a meta-analysis of 55 data sets from 3 independent sources to quantify the ammonia-N lost during the interval of time from when the liquid manure exited the irrigation equipment and when a sample was collected on the ground. The complete review, data analysis, and the data used were provided by Chastain (2019).
What Did We Do?
The study included data from traveling gun, center pivot, and impact sprinkler irrigation of untreated liquid and slurry manure, lagoon supernatant, and effluent from an oxidation ditch. The data sets included measurements of the total solids content (TS, %), total ammoniacal N concentration (TAN = ammonium-N + Ammonia-N), and total nitrogen (TKN) for a sample collected from the lagoon or storage to describe what was in the manure that left the irrigation nozzle and measurements of the TS, TAN and TKN in the samples that were collected from containers on the ground. The concentrations of TS, TAN, and TKN in the ground collected manure samples were plotted against the TS, TAN, and TKN concentrations in the irrigated manure. The data pairs were analyzed using linear regression to determine if there was a statistically significant difference between the irrigated and ground collected samples. If there was perfect agreement the slope of the line would be 1.0. Therefore, statistical tests were used to determine if the slope of the line was statistically different from 1.0. If the test indicated that the slope was not significantly different from 1.0 then irrigation did not change the concentration of the TS, TAN, or TKN.
What Have We Learned?
Well-known data used in irrigation design indicates that evaporation loss during irrigation ranges from 1% to 3.5%. The plot of the data for irrigated manure is shown in Figure 1. It was determined that the slope of the regression line was statistically greater than 1.0. Therefore, evaporation losses were small, 2.4%, and agreed with previous studies on irrigation performance.
The plot of the TAN concentrations collected on the ground and the TAN contained in the irrigated water is shown in Figure 2.). The results showed that irrigation of manure did not result in a change in the concentration of TAN. Therefore, irrigation of manure did not cause ammonia-N loss.
The same type of analysis was done for the total nitrogen data to serve as check on the TAN results. As expected, the analysis showed that irrigation did not significantly alter the concentration of TKN.
A previous study reported TAN losses ranging from 10% to 25% during irrigation of liquid manure. Error analysis of the techniques used in these studies indicated that most of the average ammonia-N loss predicted was due to volume collection error in the irrigate-catch technique that was used, and not evaporation and drift as was assumed (see Chastain, 2019). It was concluded that irrigation, as a manure application method, did not increase ammonia-N losses. These results do not imply that ammonia volatilization after manure strikes the ground is to be ignored. The suitability of irrigation as a liquid manure application method should be evaluated based on the level of treatment and the potential impact of odors on neighbors.
These results are being used in extension programs and to help refine estimates of ammonia-N loss associated with land application of manure.
John P. Chastain, Professor and Extension Agricultural Engineer, Agricultural Sciences Department, Clemson University
Corresponding author email address
Chastain, J.P. 2019. Ammonia Volatilization Losses during Irrigation of Liquid Animal Manure. Sustainability 11(21), 6168; https://doi.org/10.3390/su11216168.
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