Purpose
The amount of nitrogen lost to the air as ammonia following the application of manure is important for two reasons. From the farmer’s point of view, the loss of nitrogen as ammonia gas represents a loss of fertilizer that could have contributed to the production of a crop. From an environmental point of view, ammonia lost from a field to the atmosphere is a source of air pollution that can combine with sulfites and nitrates in the atmosphere to form extremely fine particulate matter (PM2.5) that can have harmful effects on human health and can contribute to water pollution when deposited into surface water by rainfall. Land application of animal manure is one of many sources of ammonia emissions that also include municipal and industrial waste treatment, use and manufacture of fertilizers, combustion of fossil fuel, coke plants and refrigeration (USEPA, 1995).
Animal manure can be used as a fertilizer substitute. However, the types of nitrogen in manure are more complicated than those found in most common chemical fertilizers. Nitrogen can be present in manure as ammonium-N, ammonia-N, organic-N, and nitrate-N. Not all the nitrogen in manure is immediately available for plant use. Most animal manure contains very little nitrate-N and as a result it is typically not measured. However, manure that receives aerobic treatment, i.e., composting or aeration, should be analyzed for nitrate-N since it is a valuable form of nitrogen that is the same as contained in one of the most common types of fertilizer – ammonium nitrate.
Most laboratories measure the total ammoniacal nitrogen content (TAN) of animal manure, which includes ammonium-N and ammonia-N (TAN = NH4+-N + NH3 -N). The amount of TAN that is in the ammonia form depends greatly on the pH of the manure. At a pH of 6.5 none of the TAN is in the ammonia form – it is all ammonium-N which is a great form of plant fertilizer. At a high pH, such as, 9.5, 65% of the TAN is in the ammonia form. Most animal manures have a pH in the range of 8 to 8.5 and about 10% most of the TAN is ammonia-N and can be lost to the air. As a result, TAN is often labeled as ammonium-N on manure analysis reports.
A key aspect of using animal manure as a fertilizer substitute is to make a good estimate of the fraction of the total nitrogen contained in the animal manure that can be used to grow a plant. This portion of the nitrogen is called the plant available nitrogen (PAN) and can be estimated using the following equation:
| PAN =mf Organic-N + Af TAN + Nitrate-N. | (1) |
Most of the nitrogen in untreated slurry and solid animal manure is organic nitrogen (organic-N) that must be mineralized in the soil to become available to plants as ammonium-N. The fraction of the organic-N that will be mineralized during the growing season is represented in equation 1 as the mineralization factor, mf. The value of the mineralization factor varies depending on animal species, the amount of treatment, as well as soil pH, moisture, and temperature. The values of mf recommended are 0.70 for lagoon water and 0.50 for swine slurry (Chastain, 2006).
The fraction of TAN in manure that will be available to the plant is represented by the ammonium-N availability factor, Af. The ammonium-N availability factor (a decimal) is determined from the fraction of TAN lost to the air as ammonia-N using the following formula:
| Af =1-( AL/ 100). | (2) |
The amount of ammonia-N lost following application varies with the method of application, the extent and timing of incorporation in the soil by disking as well as the pH of the manure, the pH that the manure attains following application, and the air temperature. Most extension publications provide recommended values for estimating ammonia-N losses. For example, Clemson Cooperative Extension (CAMM, 2005) recommends use of an ammonia loss (AL) of 50% for broadcast of manure without incorporation. This would mean that a value of 0.5 is used for ammonium-N availability factor (Af) in equation 1. If the manure is incorporated into the soil within one day the recommended value for AL is 20% giving an Af value of 0.80.
The amount of nitrate-N contained in animal manure is often so small that it is not measured. However, manure that is exposed to enough air or that is treated aerobically will have a significant amount and measurement of the nitrate-N content is recommended. All the nitrate-N contained in manure is 100% plant available.
Various studies and reviews (Chastain, et al., 2001; Montes, 2002; Montes and Chastain, 2003; Chastain, 2006) have indicated that the amount of ammonia lost following application of animal manure varies much more than indicated by most extension recommendations (e.g., CAMM, 2005). The result of large differences between recommended estimates and actual values is either substantial over or under estimation of the amount of ammonia emissions to the air as well as over or underestimation of the amount of nitrogen that will be available for the plant. The objective of this paper is to provide practical recommendations for the ammonium-N availability factors for swine manure based on the application method, total solids content, and the time between broadcast and incorporation.
What Did We Do?
The data and the correlations used to develop the recommendations in this paper were provided by Montes (2002) and Chastain (2006). The effect of the application method on ammonia-N loss was estimated using the following equation:
| AL =fA ALBC. | (3) |
The application factors, fA, that correspond to an application method are given in Table 1 and ALBC was the ammonia loss for broadcast manure. The value of the ammonium-N availability factor, Af, for each application method was calculated using the definition given previously in equation 2.
How fast ammonia is lost following broadcast application of manure was determined by Montes (2002). The results indicated that ammonia-N loss following irrigation of lagoon water occurred too quickly to consider incorporation by disking. Values for broadcast and incorporation for slurry manure are given in Table 1. The results indicated that incorporation must follow broadcast of slurry manure within 8 hours if it is desired to reduce ammonia-N loss by 50% (fA=0.50).
| Table 1. Application method factors to describe the reduction in ammonia loss as compared to broadcast application of manure. (Values based on reviews of the literature by Chastain et al., 2001 and Montes, 2002). | ||
| Application Method | fA | What type of manure can use this method? |
| Broadcast without incorporation | 1.0 | All |
| Broadcast followed by incorporation within 4 hoursA | 0.29 | Slurry |
| Broadcast followed by incorporation within 6 hoursA | 0.40 | Slurry |
| Broadcast followed by incorporation within 8 hoursA | 0.50 | Slurry |
| Broadcast followed by incorporation within 12 hoursA | 0.64 | Slurry |
| Band spreading (drop or trailing hose) | 0.50 | Liquid and Slurry |
| Band spreading with immediate shallow soil cover | 0.12 | Liquid and Slurry |
| Shallow injection (2 to inches below soil surface) | 0.10 | Liquid and Slurry |
| Deep injection (4 to 6 inches below soil surface) | 0.08 | Liquid and Slurry |
| AfA calculated using K = 0.086 h-1 (Chastain, 2006) |
A few studies indicated that application of manure to bare soil versus cut hay, or plant residue reduced ammonia-N loss following broadcast by 10% to 20% (see Montes, 2002 and Chastain, 2006). However, it was decided that there was not sufficient data to generalize the result for practical use.
What Have We Learned?
The model was applied to as wide a range of swine manure application situations as possible. The results were tabulated as ammonium-N availability factors, Af, that may be used in the PAN equation (equation 1) along with an estimate for the mineralization factor.
Variation in Ammonium-N Availability by Application Method
The impact of application method on the ammonium-N availability factor for swine manure is shown in Table 2. Application method had the least impact on irrigation of surface water from an anaerobic treatment lagoon. The value of Af was 0.98 for irrigated swine lagoon water. This corresponded to an ammonia-N loss of 2% (AL = (1-Af) x 100). The amount of ammonia-N lost was low since more than 0.25 inches of lagoon water was applied, and most of the ammonium-N was washed into the soil. However, the ammonium-N availability factors for broadcast of manure decreased sharply as the total solids content of swine manure increased. This corresponded to ammonia-N loss ranging from 8% for liquid manure (TS = 1% to 4%) to 58% for thick slurry (TS = 15% to 20%). It can also be seen in the table that all the ammonium-N conserving application methods increased in effectiveness as the TS content of swine manure increased.
| Table 2. Variation in ammonium nitrogen availability factors, Af, for swine manure and treatment lagoon surface water based on application method. (AL = (1 – Af) x 100) | ||||||
| Description | Broadcast or Large Bore Irrigation | Broadcast followed by incorporation within 6 hours | Band Spreading | Band Spreading with Shallow Cover | Shallow Injection | Deep Injection |
| Lagoon Surface WaterA | 0.98 | NA | 0.99 | 1.00 | 1.00 | 1.00 |
| Liquid or SlurryB | ||||||
| TS=1% to 4% | 0.92 | 0.97 | 0.96 | 0.99 | 0.99 | 0.99 |
| TS=5% to 6% | 0.82 | 0.93 | 0.91 | 0.98 | 0.98 | 0.99 |
| TS=7% to 8% | 0.75 | 0.90 | 0.88 | 0.97 | 0.98 | 0.98 |
| TS=9% to 12% | 0.66 | 0.86 | 0.83 | 0.96 | 0.97 | 0.97 |
| TS=13% to 14% | 0.56 | 0.82 | 0.78 | 0.95 | 0.96 | 0.96 |
| TS=15% to 20% | 0.42 | 0.77 | 0.71 | 0.93 | 0.94 | 0.95 |
| AALBC = 14.30 TS – 4.75, R2 = 0.791, TS = 0.5%, Chastain (2006) | ||||||
| BALBC = 23.284 TS, R2 = 0.875, Chastain (2006) | ||||||
Comparison of the Use of New Ammonium-N Availability Factors and Current Clemson Extension Recommendations for Broadcast Application of Swine Manure
Selection of the ammonium-N availability factor (Af) and mineralization factor (mf) for a manure type and application method has a large effect on the accuracy of the estimate of nitrogen that can be used to fertilize a crop as well as the estimate of ammonia-N lost to the air. The PAN estimate determines the amount of manure applied per acre (gal/ac) and the amount of P2O5 and K2O that are applied (lb/ac). The impact of using constant values of Af and mf that are different from values that more closely match the data was studied by comparing the results for spreading lagoon water (TS = 0.5%) and slurry (TS = 7.5%) to meet a target application rate of 100 lb PAN/ac. The results are provided in Table 3. The impact of settling and biological treatment in the lagoon was indicated by the low TS content (TS=0.5%) and the fact that the lagoon water contained two pounds of TAN for every pound of organic-N. Swine slurry (TS = 7.5%) contained 1.2 pounds of TAN per pound of organic-N.
Comparison of the estimates using Clemson Extensions current recommendations with the results provided in this paper led to the following observations.
-
- Using the new Af and mf values that varied by manure type (lagoon water vs slurry) provided higher PAN estimates than the Clemson Extension recommendations.
- The higher PAN estimates resulted in reductions in the amount of manure needed to provide 100 lb PAN/ac.
- The amount of ammonia-N lost per acre per 100 lb PAN applied was much lower using the new factors for estimating PAN as compared to using Clemson Extension values for lagoon water and swine slurry. Using Clemson Extension values over-estimated the ammonia-N loss/ac by 133% to 1133%.
- The inaccuracies in PAN estimates for lagoon water and slurry manure also impacted plant nutrient application rates. Using the PAN estimates based on Clemson Extension recommendations to determine manure application rates resulted in over application of nitrogen by 17% to 21%. Similar over-applications were observed for P2O5 and K2 Therefore, better estimates of PAN can help to reduce excessive applications of phosphorous and provide better estimates of potash (K2O) application rates.
- Comparison of the estimates of the ammonia-N lost per acre following broadcast of manure for the examples shown in Table 4 demonstrates the need to consider using values of Af and mf that more closely agree with the available data.
- It must be emphasized that slurry manure with a higher TS content than 7.5% and heavily bedded manure were not included in the examples in this paper. The ammonia-N loss values will be higher and must be calculated using the Af values provided in this paper along with the corresponding manure analysis to yield valid conclusions.
Impact of Selected Ammonium-N Conserving Application Methods on Ammonia-N Loss per Acre, and P2O5 Application Rate
The impact of application method on the estimates of PAN, ammonia-N loss, and phosphorous application rates was calculated for swine slurry using the tabulated values for the ammonium-N availability factors given in Table 2. Lagoon water was not included because irrigation is the most common and cost-effective method of application, and the amount of ammonia-N lost to the air was the least. The application methods that were compared were broadcast, broadcast followed by incorporation within 6 hours, band spreading, band spreading with shallow soil cover, and shallow injection. Results for deep injection were not included because the improvements were very small compared with shallow injection (see Table 2). Furthermore, the horsepower and fuel costs of deep injection are higher than for shallow injection. The results are given in Table 4.
The results indicated that broadcast with incorporation within 6 hours provided a reduction in ammonia-N loss per acre of 65% and a reduction in the P2O5 application rate of 11%. Band spreading provided almost the same benefits (57% reduction in ammonia-N loss and 10% reduction in lb P2O5/ac) but would be achieved with only one pass across a field. Adding a method to immediately cover a band of manure with soil provided reductions in ammonia-N loss of 90% and reduction of the P2O5 application rate by 16%. Shallow injection provided a modest improvement in ammonia-N emissions (93%) as compared to band spreading with shallow cover. Shallow injection also provided about the same benefit in reduction of phosphorous application rate as band spreading with shallow cover.
| Table 3. Comparison of land application rate and ammonia-N loss estimates using tabulated model results and current Clemson University Extension recommendations for broadcast application of swine lagoon surface water and slurry manure. Target nutrient application rate = 100 lb PAN/ac. | ||
| Swine | ||
| Lagoon Water | Slurry | |
| TS, % | 0.5 | 7.5 |
| TAN, lb/1000 gal | 4.3 | 23.0 |
| Org-N, lb/1000 gal | 2.0 | 19.0 |
| P2O5, lb/1000 gal | 3.6 | 33.0 |
| K2O, lb/1000 gal | 7.9 | 28.0 |
| Land Application Rates and Ammonia-N Loss Estimates Using Clemson Extension Recommendations | ||
| Mineralization factor, mf | 0.60 | 0.60 |
| Ammonium-N availability factor, Af | 0.80 | 0.50 |
| PAN estimate, lb PAN/1000 gal | 4.6 | 22.9 |
| Application rate to provide 100 lb PAN/ac, gal/ac | 21,552 | 4,367 |
| Resulting application rate for P2O5, lb/ac | 78 | 144 |
| Resulting application rate for K2O | 170 | 122 |
| Ammonia-N Loss, lb per acre / 100 lb PAN | 18.5 | 50.2 |
| Land Application Rates and Ammonia-N Loss Estimates Using New Recommendations | ||
| Mineralization factor, mf | 0.70 | 0.50 |
| Ammonium-N availability factor, Af | 0.98 | 0.75 |
| PAN estimate, lb PAN/1000 gal | 5.6 | 26.8 |
| Application rate to provide 100 lb PAN/ac, gal/ac | 17,813 | 3,738 |
| Resulting application rate for P2O5, lb/ac | 64 | 123 |
| Resulting application rate for K2O | 141 | 105 |
| Ammonia-N Loss, lb per acre / 100 lb PAN | 1.5 | 21.5 |
| Key Impacts of Inaccurate Estimates of Af, and PAN | ||
| Over-estimation of Ammonia-N Loss/ac | 1133% | 133% |
| Actual PAN Application Rates Using Clemson Extension Recommendations to Determine Manure Application Rate, lb PAN/ac and percent over-application of PAN (%) | 121 (21%) |
117 (17%) |
| Difference in Application of P2O5, lb/ac (%) | 14 (22%) |
21 (17%) |
| Difference in Application of K2O, lb/ac (%) | 29 (21%) |
17 (14%) |
| Table 4. Impact of Application Method on Ammonia-N Loss and P2O5 Application Rate for Swine Slurry. The total solids and plant nutrient contents were given previously in Table 3 and the mineralization factor was 0.50 for all application methods. | |
| Swine Slurry, TS = 7.5% |
|
| Broadcast – no incorporation | |
| Mineralization factor, mf | 0.50 |
| Ammonium-N availability factor, Af | 0.75 |
| PAN estimate, lb PAN/1000 gal | 26.8 |
| Application rate to provide 100 lb PAN/ac, gal /ac | 3,738 |
| Resulting application rate for P2O5, lb/ac | 123 |
| Ammonia-N Loss, lb per acre / 100 lb PAN | 21.5 |
| Broadcast – incorporation within 6 hours | |
| Ammonium-N availability factor, Af | 0.90 |
| PAN estimate, lb PAN/1000 gal | 30.2 |
| Application rate to provide 100 lb PAN/ac, gal /ac | 3,311 |
| Resulting application rate for P2O5, lb/ac | 109 |
| Ammonia-N Loss, lb per acre / 100 lb PAN | 7.6 |
| Reduction in Ammonia-N loss Compared to Broadcast | 65% |
| Reduction in P2O5 Application Rate | 11% |
| Band Spreading |
|
| Ammonium-N availability factor, Af | 0.88 |
| PAN estimate, lb PAN/1000 gal | 29.7 |
| Application rate to provide 100 lb PAN/ac, gal /ac | 3,362 |
| Resulting application rate for P2O5, lb/ac | 111 |
| Ammonia-N Loss, lb per acre / 100 lb PAN | 9.3 |
| Reduction in Ammonia-N loss Compared to Broadcast | 57% |
| Reduction in P2O5 Application Rate | 10% |
| Band Spreading with Shallow Cover |
|
| Ammonium-N availability factor, Af | 0.97 |
| PAN estimate, lb PAN/1000 gal | 31.8 |
| Application rate to provide 100 lb PAN/ac, gal /ac | 3,144 |
| Resulting application rate for P2O5, lb/ac | 104 |
| Ammonia-N Loss, lb per acre / 100 lb PAN | 2.2 |
| Reduction in Ammonia-N loss Compared to Broadcast | 90% |
| Reduction in P2O5 Application Rate | 16% |
| Shallow Injection | |
| Ammonium-N availability factor, Af | 0.98 |
| PAN estimate, lb PAN/1000 gal | 32.0 |
| Application rate to provide 100 lb PAN/ac, gal /ac | 3,121 |
| Resulting application rate for P2O5, lb/ac | 103 |
| Ammonia-N Loss, lb per acre / 100 lb PAN | 1.4 |
| Reduction in Ammonia-N loss Compared to Broadcast | 93% |
| Reduction in P2O5 Application Rate | 17% |
Future Plans
The model results provided in this paper are currently being used to develop extension programs and will be used to update extension publications and recommendations for producers. It is hoped that these tabulated ammonium-N availability factors will be used to increase the precision of using swine manure as a fertilizer substitute and making better estimates of ammonia-N emissions.
Author
John P. Chastain, Professor and Extension Agricultural Engineer, Agricultural Sciences Department, Clemson University
Corresponding author email address
Additional Information
CAMM. 2005. Confined Animal Manure Managers Program Manual – Swine Version. Clemson, SC.: Clemson University Extension. Available at https://www.clemson.edu/extension/camm/manuals/swine_toc.html.
Chastain, J.P. 2006. A Model to Estimate Ammonia Loss Following Application of Animal Manure, ASABE Paper No. 064053. St. Joseph, Mich.: ASABE.
Chastain, J. P., J. J. Camberato, and J. E. Albrecht. 2001. Nutrient Content of Livestock and Poultry Manure. Clemson, SC.: Clemson University.
Montes, F. 2002. Ammonia volatilization resulting from application of liquid swine manure and turkey litter in commercial pine plantations. MS Thesis, Clemson, SC.: Clemson University.
Montes, F., and J.P. Chastain. 2003. Ammonia Volatilization Losses Following Irrigation of Liquid Swine Manure in Commercial Pine Plantations. In Animal, Agricultural and Food Processing Wastes IX: Proceedings of the Nineth International Symposium, 620-628. R.T. Burnes, ed. St. Joseph, Mich.: ASABE.
USEPA. 1995. Control and Pollution Prevention Options for Ammonia Emissions (EPA-456/R-95-002), report prepared by J. Phillips, U.S. Environmental Protection Agency, Control Technology Center. Research Triangle Park, NC. Available at https://www.epa.gov/sites/default/files/2020-08/documents/ammoniaemissions.pdf.
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