Ammonia Volatilization from Urea, Mechanisms, Magnitude, and Management

Transcription

1 Ammonia Volatilization from Urea, Mechanisms, Magnitude, and Management David E. Kissel University of Georgia

2 Overview Urea Consumption Definitions UAN Solution Reactions Urea Dissolution and Diffusion Urea Hydrolysis Ammonia Volatilization Research Results Summary

3 World Evolution of N Fertilizer Consumption Urea 51% Ammonium nitrate Nitrogen solutions 1973 / / 05 Ammonium phosphate Total compound N Millions of tonnes

4 USA Evolution of N Fertilizer Consumption Urea 21% Ammonium nitrate Nitrogen solutions 1973 / / 05 Anhydrous ammonia Total compound N Millions of tonnes

5 Overview Urea Consumption Definitions UAN Solution Reactions Urea Dissolution and Diffusion Urea Hydrolysis Ammonia Volatilization Research Results Summary

6 Definitions Dissolution: urea absorbs water and converts from solid to liquid Hydrolysis: urea converts to ammonium (NH 4 ) Diffusion: movement due to motion of molecules Urea has no charge, diffuses easily NH 4 has charge, diffuses slowly

7 Overview Urea Consumption Definitions UAN Solution Reactions Urea Dissolution and Diffusion Urea Hydrolysis Ammonia Volatilization Research Results Summary

8 Q. Does any ammonia volatilize from UAN solutions before they are applied or during the application? A. None or very little, depending on if a small amount of ammonia is added to protect against corrosion of mild steel.

9 Composition of UAN 28% N 14 % N from Ammonium Nitrate 7% ammonium N 7% nitrate N 14% N from Urea 30% water small amounts of inhibitors to inhibit corrosion of mild steel

10 Inhibitors to protect against corrosion of mild steel 0.5 % ammonia (raises ph to about 7.5) Ammonium phosphates at 0.2 % P 2 O 5 Others

11 NH4 NH4 4 = NH NH3 3 H H NH 4 = H (ion) (gas)

12 Urea Hydrolysis in UAN? DOES NOT OCCUR Therefore no ammonia is formed from the urea portion of the UAN solution from this process. Therefore no ammonia loss from the urea portion of UAN solution before soil application.

13 Summary of ammonia loss from UAN Urea in UAN does not hydrolyze in the fertilizer tank. The NH 4 from the ammonium nitrate portion of the UAN cannot be lost as. The amount of added to some UAN to inhibit corrosion is very small, around 10 lb per ton. A small portion of this may be lost during application.

14 Overview Urea Consumption Definitions UAN Solution Reactions Urea Dissolution and Diffusion Urea Hydrolysis Ammonia Volatilization Research Results Summary

15 Urea Dissolution Urea has to be dissolved before it can be hydrolyzed

16 Urea Dissolution Urea has to be dissolved before it can be hydrolyzed Urea can absorb water from the atmosphere and from the soil/crop residue

17 Urea Dissolution Urea has to be dissolved before it can be hydrolyzed Urea can absorb water from the atmosphere and from the soil/crop residue Absorption of water from the atmosphere depends on relative humidity (RH)

18 Urea Dissolution Urea has to be dissolved before it can be hydrolyzed Urea can absorb water from the atmosphere and from the soil/crop residue Absorption of water from the atmosphere depends on relative humidity (RH) Critical relative humidity (CRH) is the RH at which urea dissolves

19 Critical Relative Humidity for Urea (%) Effect of Temperature on CRH and Water Solubility of Urea CRH Solubility Air Temperature ( o F) Urea Solubility (lb/gallon of water)

20 Urea dissolution and diffusion RH > CRH (80%) Urea Urea Urea Crop residue Dry Soil

21 Urea dissolution and diffusion Urea Urea Urea Crop residue 1/2 inch Urea Urea Urea Wet Soil

22 Urea Diffusion into Soil (after 10 days) Urea Concentration in Soil (ppm) Wetter Soil Depth (mm) Drier 50

23 Urea Urea Urea Crop residue 2 inches Urea Urea Urea

24 Overview Urea Consumption Definitions UAN Solution Reactions Urea Dissolution and Diffusion Urea Hydrolysis Ammonia Volatilization Research Results Summary

25 Urea Hydrolysis Urea 2 H 2 NH 4 Urease enzyme Urease is derived from crop residues and soil microorganisms

26 Urease inhibitor Urea Urea Urea Crop residue Urea Urea Urea

27 Overview Urea Consumption Definitions UAN Solution Reactions Urea Dissolution and Diffusion Urea Hydrolysis Ammonia Volatilization Research Results Summary

28 Volatilization Process Atmosphere Hydrolysis Urea 2 H 2 NH 4 Clay OM NH 4 NH 4 NH 4 Soil air Soil solution (gas) NH 4 (aq) Equilibrium NH (aq) 3 H

29 Effect of soil ph on as % of Total N (as % of Total Ammoniacal N) o F Soil ph

30 Volatilization Process Atmosphere Hydrolysis Urea Clay OM H NH 4 NH 4 NH 4 NH NH 3 4 Soil air Soil solution (gas) NH 4 (aq) Equilibrium NH (aq) 3 H

31 Increase in soil ph depends on soil H buffering capacity Loss (kg N ha -1 ) Low Buffering Capacity High Buffering Capacity Higher clay and OM contents lead to higher soil H buffering capacity Soil ph Low Buffering Capacity High Buffering Capacity Ferguson et al. (1984) Days Since Urea Application

32 Atmosphere Urea Urea Urea Urea NH 4 4 NH 3 4 NH 4 H 4 NH NH 4 4 H 4 H H H H H H CEC Urea hydrolyzes on the soil surface ½ inch ph

33 Urea hydrolyzes below the soil surface Urea Urea Urea Urea Urea Urea Urea Urea NH NH 4 4 NH 4 4 NH NH NH H 4 NH 4 4 H 4 H H H H H H CEC ph inches

34 Effect of Temperature on Volatilization Temperature Soil ½ inch Urea H NH 4

35 Effect of Temperature on Urea Hydrolysis 6 Relative Urease Activity Temperature ( o F) Gould et al. (1973)

36 Effect of Temperature on Volatilization Temperature Soil ½ inch Urea H NH 4

37 Effect of Temperature on % of (as % of Total Ammoniacal N) ph = Temperature ( o F)

38 Effect of Temperature on Volatilization Temperature Soil ½ inch Urea H NH 4

39 Effect of Temperature on Conversion of Aqueous to Gaseous Relative Driving Force for Conversion of Aqueous to Gaseous Temperature ( o F)

40 Effect of Temperature on Volatilization Temperature Soil ½ inch Urea H NH 4

41 Effect of Wind Speed on Volatilization Atmosphere Wind speed Soil Urea NH 4 H ½ inch

42 Ammonia Loss (% of Applied N) Wind Speed (m s -1 ) 20 UAN UREA Nitamin 15 Replication I mm 0 20 UAN UREA Nitamin Replication II 5 4 High Low mm UAN UREA Nitamin 51mm Replication III 0 00:00:00 08:00:00 16:00:00 00:00:00 Time Days After Application

43 Optimum Conditions for Volatilization Small diffusion depth into soil RH > CRH High temperature High wind speed Low ph buffering capacity

44 Overview Urea Consumption Definitions UAN Solution Reactions Urea Dissolution and Diffusion Urea Hydrolysis Ammonia Volatilization Research Results Summary

45 Rainfall (mm) Soil water content (g g -1 ) loss (% of applied N) Urea Applied to Pasture - Fall Nitamin UAN Urea Temp = 47 o F Rainfall Soil water content Days after application

46 Urea Applied to Pasture Spring 2005 loss (% of applied N) Rainfall (mm) Soil water content (g g -1 ) Nitamin UAN Urea Temp = 63 o F Rainfall Soil water content Days after application

47 Atmosphere Urea Urea Urea Urea NH 4 Urea NH 4 Urea NH 4 Clay OM NH (aq) 4 (aq) NH H 3 Equilibrium

48 Urea Applied to Pasture - Fall 2005 loss (% of applied N) Rainfall (mm) Soil water content (g g -1 ) Nitamin UAN Urea Temp = 62 o F Rainfall Soil water content Days after application

49 Time of RH > CRH (h) Time of RH above CRH in the first 30 d Days after application Total: RH > CRH =19 63 days %

50 Atmosphere RH > CRH (80%) NH NH NH NH NH 4 4 Urea Urea Urea NH 4 NH 4 Fescue thatch Soil water content (0.07 g g -1 ) Permanent wilting point (0.04 g g -1 )

51 Urea Applied to Pasture Spring 2006 loss (% of applied N) Rainfall (mm) Soil water content (g g -1 ) Nitamin UAN Urea Temp = 69 o F Rainfall Soil water content Days after application

52 Atmosphere NH 4 CEC Urea Urea Urea NH 4 Urea Urea Urea NH 4 NH NH NH (aq) 4 (aq) 3 H 3 Equilibrium Soil water content (0.15 g g -1 ) Field capacity (0.18 g g -1 )

53 Ammonia volatilization losses under field conditions Fertilizer Urea UAN Summary of Pasture Results Nitamin Fall Ammonia loss (% of applied N) a* 6 b 6 b Spring a 13 a 14 a Fall 2005 Spring a 33 b 34 b 24 a 18 a 18 a Within a column, values followed by the same letter are not significantly different according to Fisher s LSD at p=0.05

54 Summary for Pastures/No-Till Dry Soil, Dry Residue, RH < CRH: OK Dry Soil, Dry Residue, RH > CRH: not OK Wet Soil, Wet Residue: not OK Apply on dry soil, dry residue, expected low RH, and hope for 1 inch of rain whenever it rains. Apply on wet soil if 1 inch rain/irrigation is expected.

55 Summary for Clean-Till Crops Dry Soil: OK Wet Soil: not OK Apply on dry soil and hope for 1 inch of rain whenever it rains. Apply on wet soil if 1 inch of rain/irrigation is expected.

56 Knifed of disked in better than Dribbled Dribbled better than Broadcast Summary for Pastures/Crops Knifed or disked in Dribbled Broadcast

57 Urea Applied to Pine Plantations Loss (% of Applied N) May 2 - May 31, mm 0 mm 20 mm Rain 66 o F Days After Application

58 Laboratory Results (77 o F, 90% RH) Cumulative Loss (% of Applied N) mm before urea 20 mm right after urea 20 mm 1 day after urea 20 mm 3 days after urea 5 mm rain added to all treatments Days After Urea Application

59 Pine needle photo Urea NH 4 NH 4 CEC CEC Organic Layer

60 Pine needle photo Urea Urea NH 4 NH 4 NH4 NH 4 NH 4 CEC CEC Organic Layer

61 Summary for Pine Plantations Dry Forest Floor, RH < CRH: OK Dry Forest Floor, RH > CRH: not OK Wet Forest Floor: not OK Apply on dry forest floor, with expected low RH, and hope for 1 inch of rain whenever it rains. Apply on wet forest floor if 1 inch rain is expected.

62 Questions?

63 Atmosphere NH 3 Urea Urea Urea NH NH NH NH NH 4 4 NH 4 NH 4 Fescue thatch or OM NH 4 NH 4 CEC CEC

64 Loss (% of Applied N) Laboratory Results (77 o F, 90% RH) volatilization in the lab 30 Urea UAN a b b 0 Nitamin Days after application