Ammonia Volatilization from Manure Application

The purpose of this factsheet is to provide producers and farm managers with information that will help quantify the amount of ammonia loss that occurs when they apply manure on land. It also provides them with information regarding the factors that positively and negatively affect these losses.

The factsheet is also a good source of information on best management practices producers could use to mitigate and control ammonia losses from the land application of manure.

Sources of Ammonia

Agricultural activities (livestock production and fertilizer application) have been identified as the major sources of atmospheric ammonia emissions in Alberta, followed by biomass burning. Within agricultural activities, ammonia emissions into the atmosphere occur primarily from livestock buildings, open feedlots, manure storage facilities, during manure handling and treatment and when manure is applied on land.

Ammonia in livestock facilities results primarily from the breakdown of urea by the enzyme urease. In most livestock, urea is only present in the urine while urease is present in the feces. In poultry, urease is excreted with uric acid in the feces.

Most efforts to control ammonia losses from livestock operations have been focused on the land application of manure because the practice contributes largely to the overall ammonia losses from agriculture. Ammonia losses following land application of manure could reach up to 95 per cent of the total manure nitrogen-ammonium (N-NH₄) content. The amount of N-NH₄ lost depends on the manure characteristics and the environmental conditions.

Ammonia volatilization (gassing off) decreases the nutrient value of manure and results in a significant loss of its nitrogen. It also has a negative effect on the environment, such as soil acidification and eutrophication (deprivation of oxygen). Ammonia lost to the atmosphere combines with nitric acid to form airborne nitrate particles that have serious effects on human health and can cause visibility impairment.

Factors Affecting Volatilization

Significant volatilization of ammonia can occur within the first 24 hours after the land application of manure. More than 50 per cent of the total emission of ammonia can occur within the first six hours after application. Ammonia volatilization is highly dependent on manure management techniques and environmental factors.

1. Manure type and characteristics
Manure characteristics such as total nitrogen (TN), ammonium nitrogen (NH4-N) and percentage of dry matter (% DM) play an important role in ammonia volatilization during manure application to soils. Generally, liquid manure and slurry have a high rate of ammonia loss compared to solid manure. The dry matter content has been shown to significantly affect ammonia volatilization. Reducing the dry matter content of dairy manure by dilution or separation has been shown to reduce ammonia emissions following land application.

2. Environmental factors

• Temperature: Solar radiation increases the temperature of the manure. As manure temperature increases, ammonia volatilization increases, especially within the first few hours after manure is applied to the soil (50%). Researchers have found that 50 per cent of total nitrogen is volatilized as ammonia at a temperature of 30°C compared to 35 per cent when the temperature is 25°C. Manure applications should not be made when temperatures are high.
• Wind: An increase in wind speed will increase the rate of ammonia volatilization as the higher wind increases the mass transfer and air exchange between the manured surface and the atmosphere. Manure should be applied when the wind speed is low, and the weather is stable.
• Rainfall: Rainfall directly after manure application decreases the volatilization of ammonia because the rain improves infiltration of the ammonia into the soil and also reduces its evaporation. Generally, ammonia emissions decrease with an increase in relative humidity.

500 tonnes * 2.4 kg/tonne = 1,200 kg of ammonia

1,200 kg * 0.25 = 300 kg of ammonia

1,200 kg * 0.31 = 370 kg of ammonia

1,200 – 300 kg = 900 kg of ammonia

1,200 – 370 kg =830 kg of ammonia

500 tonnes * 2.4 kg/tonne = 1,200 kg of ammonia

1,200 kg * 0.75 = 900 kg of ammonia

1,200 – 900 kg = 300 kg of ammonia

Day after application	Average	Cool (<10°C)		Warm (>25°C)
		Wet	Dry	Wet	Dry
Spring
Incorporated within 1 day	25	10	15	25	50
Incorporated within 2 days	30	13	19	31	57
Incorporated within 3 days	35	15	22	38	65
Incorporated within 4 days	40	17	26	44	73
Incorporated within 5 days	45	20	30	50	80
Not incorporated	66	40	50	75	100
Injected	0	0	0	0	0
Fall
Early fall applied	66	40	50	75	100
Late fall applied	25	25	25	N/A	N/A
Cover crop	35	25	25	40	40

• Direct injection of manure into the soil reduces ammonia losses compared to surface application methods. The reduction in ammonia emissions by injection could reach up to 100 per cent (Table 2), but it will also result in the increase of nitrous oxide emissions from agricultural soils by up to 100 per cent. The costs to inject manure are estimated to be $0.003 per gallon above the cost to haul and spread liquid manure. By injecting the manure, a portion of the added cost can be recaptured agronomically in the form of reduced nitrogen losses compared to manure application by broadcasting.
• The incorporation of manure immediately after spreading could result in a substantial reduction in ammonia losses (see the section on “Calculating ammonia losses: how?”) as well as a possible decrease in odour emissions and run-off or discharge of manure from the manure application area. Conventional tillage equipment is generally used to incorporate surface-applied manure into the soil. The Agricultural Operations Practices Act (2004) requires that a person must not spread manure if it cannot be incorporated within 48 hours, unless the manure is spread on forage or direct seeded crops or the land is frozen or snow covered.
• Band spreading liquid manure on the soil surface but beneath the crop canopy using drop hoses or “sleighfoot” applicators can reduce ammonia emissions relative to broadcasting by up to 80 per cent. Generally, banding conserves ammonia by reducing the exposure of manure to the air, but the method works best under a crop canopy. The crop canopy both reduces advection (transfer of heat by horizontal flow of air), thereby inhibiting ammonia volatilization, and directly absorbs up to 40 per cent of any released ammonia.
• The timing of application is an important consideration affecting the release of manure nitrogen into the atmosphere. Ammonia loss is generally greater during the spring and summer. Also, incorporation time and weather affect ammonia losses. Significant volatilization occurs within the first 24 hours after application on a warm, wet or dry day (Table 2). Losses of ammonia can be reduced by night-time application. Dispersion across the landscape may require application at different times of the day.
• Research has demonstrated that some products can effectively reduce ammonia losses through either a binding or a pH effect. Dropping the manure pH below 7 before it is applied can reduce ammonia emissions. Urease inhibitors may also prove effective. Costs are product specific and often determined as much by application rate and frequency as by the cost per unit weight of the product.

• Ammonia management from manure storage and spreading. Factsheet. Nova Scotia Agricultural College. 2007
• The value and application of manure on forages. Factsheet. Ontario Ministry of Agriculture and Rural Affairs: OMAFRA. 2003
• 2004 Reference Guide Agricultural Operation Practices Act (AOPA). 2nd Edition, Alberta Agriculture and Rural Development