Volatilization Losses From Surface Applied Nitrogen

Concern over volatilization losses from surface applied nitrogen are justified during periods of high temperatures, high winds and little rain in the foreseeable future.

In the case of urea, hydrolysis converts the urea to ammonia, and if the urea is not incorporated, the ammonia is lost to the air.

Conditions favouring high volatilization potential are:

• high soil temperatures
• moist conditions, followed by rapid drying
• windy conditions
• high soil pH (>pH 7.5)
• high lime content in surface soil
• coarse soil texture (sandy)
• low organic matter content
• high amounts of surface residue (e.g. Zero tillage)
• nitrogen source: urea>UAN solution > ammonium nitrate

University of Manitoba studies indicate potential losses of 38%-46% of urea N during 5 days at 25°C versus less than 7% loss when temperatures are 15C (U of M, Toews) (Table 2.) More recent studies under zero tillage conditions at Brandon found 40% and 88% loss of urea N after 7 days in May and July, respectively (Table 3).

Our high soil pH increases volatilization losses. As soil pH increases from 6.5 to 7.5 volatilization losses double from 10% to 20% foe urea left on the surface for 4 days. (Table 4.)

The best options for farmers wishing to topdress additional N on crops are:

• Spoke wheel injection of UAN solution (28-0-0).
• Surface strip banding of UAN solution. In theory this is better than surface broadcast UAN, but little difference has been observed in Brandon studies. (A 3 year study at Penn State found average NH3 volatilization losses within 10 to 20 days of 40, 22 and 17 kg N/ha from broadcast urea, sprayed UAN and dribbled UAN, respectively. Losses from sprayed and dribbled UAN were not different, but both were significantly less than urea.)

More Volatilization Facts

a) How much rain is required to incorporate surface applied urea?

Quoted values vary from 0.1 inch or 2.5 mm (Michigan) to 0.25 inch or 6 mm (Minnesota, North Dakota).

The longer rainfall is delayed after application, the greater the volatilization losses. (Table 1)

Table 1. Effect of rainfall on N volatilization losses
Rainfall	Within days after application	N Volatilization Losses, %
0.4	2	0
0.4	3	10
0.1 to 0.2	5	10 to 30
0	5	30+

(Fox and Hoffman, Pennsylvania – N on no-till corn)

b) The influence of temperature on urea volatilizations.

 

Table 2. Percent of surface-added urea volatilized as ammonia as influenced by soil temperature and days urea was left on the soil surface (from Overdahl, et al., 1987).
	Temperature (f)
Days	45	60	75	90
	% of added N volatilized
0	0	0	0	0
2	0	0	1	2
4	2	2	4	5
6	5	6	7	10
8	5	7	12	19
10	6	10	14	20

 

Table 3. Percent of surface – applied urea volatilized in 7 days as influenced by time and N source (Grant et al, 1996.)
	Check	Urea	Urea + NBPT	UAN	UAN+ NBPT
	% of added N volatilized
May (Warm  20-25°C)	0	40	2	7	1
July (Hot 30°C)	0.6	88	12	50	16

Fertilizer was applied under zero till conditions in a nested application (similar to a dribble band).

c) The influence of Soil pH on urea volatilization

Table 4. Percent of surface-applied urea volatilized as ammonia as influenced by soil pH and days urea was left on the soil surface (from Overdahl, et al, 1987).

	Soil pH
	5.5	6.0	6.5	7.0	7.5
Days	% of added N volatilized
0	0	0	0	0	0
2	0	0	0	1	5
4	2	5	10	18	20
6	5	7	11	23	30
8	9	12	18	30	33
10	10	13	22	40	44

 

For further information, contact your GO Representative.