Enhancing Cropping System Sustainability by Minimizing Ammonia-N Losses from Biological and Chemical Inputs

2013 Annual Report for SW10-050

Project Type: Research and Education
Funds awarded in 2010: $190,009.00
Projected End Date: 12/31/2013
Grant Recipient: Montana State University
Region: Western
State: Montana
Principal Investigator:
Dr. Richard Engel
Montana State University

Enhancing Cropping System Sustainability by Minimizing Ammonia-N Losses from Biological and Chemical Inputs


Ammonia (NH3) volatilization from chemical fertilizer and legume green manure nitrogen (N) inputs represents a significant pathway of N loss to the environment. On-farm measurements of NH3 losses from these sources have rarely been conducted. This project is quantifying NH3 losses following urea fertilization and legume green manure termination using a micrometeorological method and evaluating strategies to minimize losses. Studies are being conducted on private farms with input from growers. Results are being shared with the agricultural community at field days, workshops and in popular media. Currently, there is a large gap in knowledge about the magnitude of NH3 losses from farms in the Northern Great Plains (NGP). This project will help bridge this gap, thereby improving agricultural sustainability and environmental quality.


Objectives/Performance Targets

 1.  Quantify on-farm ammonia loss from urea fertilizer applications (chemical) and legume termination (biological) from NGP dryland cropping systems.

Our performance target will be to determine the fraction of applied urea fertilizer that is lost as NH3 for applications to winter wheat applied from late fall to early spring. Our study will identify the environmental and soil conditions that are most conducive to high NH3 losses. Our second performance target will be to determine the fraction of N in legume manure that is lost as NH3 following its termination by glyphosate spraying and mowing. Most studies on NH3 volatilization have utilized enclosures or chambers rather than the micrometeorological techniques being proposed here.   Micrometeorological approaches are widely recognized as providing more reliable estimates of gas N losses than enclosures, because they do not disturb the environment or soil processes that affect gas exchange at the ground, provide continuous measurements over time and provide a measure of gas loss over a larger footprint than enclosures.

2. Identify mitigation strategies or production practices that will minimize ammonia-N losses where losses are found to be significant from inorganic and organic N inputs.

Our performance target will be to mitigate NH3 losses to ≤ 5% of the N input. We will evaluate different mitigation strategies based on comments and input received from our participating cooperators, area growers and agricultural professionals. For example, our urea studies may evaluate: i) subsurface urea banding at seeding; ii) pre-plant broadcast applications followed by direct seeding; and iii) enhanced efficiency fertilizers that include urease inhibitors. Under strategy ‘i’, most no till air-seeders have the capacity to apply both fertilizer and seed. Placement of fertilizer urea below the soil surface is a known strategy for mitigating NH3 emissions to the air. Under strategy ‘ii’, many air-drills are configured with hoe-style openers that create considerable disturbance at the soil surface. The level of disturbance may be sufficient to cover urea prills on the soil surface, thereby mitigating NH3 losses. Under strategy ‘iii,’ enhanced efficiency fertilizers have gained popularity in recent years because of their potential to enhance crop N use efficiency. Recently, NRCS programs such as the Conservation Stewardship Program (CSP) have targeted agricultural air quality issues, including NH3 pollution. The CSP provides enhancement points to growers for adopting practices that improve air quality, including enhanced N fertilizers that contain urease inhibitors.

Few reports are found in the literature that utilized micrometeorological methods to quantify NH3 volatilization losses in the field from legume green manures. Therefore, we make no prejudgments about what we might find.  Incorporation of crop residue is the most effective approach for mitigating NH3 losses. Under a strict no till scenario, tillage is not an option; however, this practice may need to be considered should NH3 losses prove significant.

3. Develop and execute an educational outreach program to producers and agricultural professionals that will improve their understanding of on-farm N cycles and N loss mitigation, thereby leading to enhanced sustainability and environmental quality.

Our performance target will be to achieve direct contact with 1,000 people (or people-hours) and indirect contact with another 5,000 people through radio, news releases and trainings by ag professionals and farmer-to-farmer communication. Our education outreach programs will target ag professionals who are involved in outreach to their grower-clients. Therefore, we anticipate there will be a multiplier effect to our direct contact hours.


Thirteen field trials have been completed (one is on-going and two more planned) on private farms in northern and central Montana since this project’s inception according to the protocol described in the proposal. These field studies were established to directly address Objectives/Performance Targets # 1 and 2. In addition, we have been engaged in an active educational outreach program to producers and professionals as stated under Objective/Performance Target #3.  A barometer of our success has been the accumulated contact hours with producers in our region. Currently, we have accumulated 1,200 contacts or 120% of our final target. A brief summary of our accumulated research results and education outreach programs is provided below.


Pre-plant urea application to mitigate ammonia losses (Fall 2010 and 2011)

Interest in investigating this mitigation strategy came as a result of our discussions with growers at meetings and one-on-one visits. During these meeting growers asked if the disturbance created by their air-seeders configured with hoe-style openers was sufficient to cover urea prills on the soil surface, thereby mitigating NH3 losses. This research directly benefits growers by addressing a management question that affects economic return from fertilizer and net income.

Field trials were conducted during the first two years of this project at four no-till wheat farm sites (Campaigns 13, 14, 15 and 17) in northern Montana according to the protocol outlined in the proposal. Urea was applied as a pre-plant (< two hours prior of seeding) and post-plant (< two hours following seeding). The post-plant urea treatment was included as a positive control to assess the potential for NH3 loss from urea without incorporation. Photographs from the field sites revealed the level of disturbance created by air-drills differed appreciably at two field sites where similar style hoe-openers were used (Figure 1). If seeding occurred under dry conditions, soil disturbance was low and most of urea prills remained visible at the surface (Figure 2). If the soil was moist at the time of seeding the level of disturbance was greater and a higher percentage of fertilizer prills were covered with soil.

Ammonia losses are summarized in Figure 3 for four trials/campaigns conducted over the two seasons. Cumulative NH3 loss for the four campaigns averaged 14.0 and 12.8% of applied N for the pre-plant and post-plant applications, respectively. There was no evidence that disturbance created by air seeders was sufficient to mitigate NH3 loss from surface-applications of urea. In three of the four trials (Campaigns 13, 15 and 17), growers seeded into a seed-bed with dry soil, similar to the conditions depicted in Figure 2 (top).  Growers in Montana frequently seed winter wheat into dry soil surface such as depicted in these photographs. Precipitation amounts and patterns following seeding have a large impact on the size and distribution of NH3 losses. Our research has shown that significant periods of NH3 loss are associated with a wet to dry cycle in the soil, which occurs after modest precipitation events are followed by a period of drying. For example, during Campaign 13, precipitation equivalent to 6 mm and 15.2 mm one day and five day post-fertilization, respectively. These events wetted the soil surface but then were followed by a period of surface drying that resulted in comparatively high NH3 losses over weeks one and two. Campaign 15 was characterized by much lower NH3 loss than Campaigns 13, 14 and 17 because very little precipitation was received at this field trial (only 7.7 mm over the first six weeks) before snow covered the field site. It is likely that a significant fraction of applied urea never hydrolyzed during this trial.  

Urea applications to during cold weather months (late fall, winter and early spring)

Growers in Montana frequently surface-apply urea during cold weather months (November-April). A question that has been asked of us during grower meetings is whether NH3 volatilization losses from urea are mitigated if applications are made to snow-covered soils and /or frozen soils. In addition, we have been asked by growers to know the potential impact of NH3 volatilization losses on yield, protein and nitrogen use efficiency/recover by the plant. These questions are presently being addressed in our study in concert with a complementary study supported by the Montana Fertilizer Advisory Committee, and the results of which will be presented in our final report (Summer 2014).

Over the past three seasons (2010-2012, 2011-2012, 2012-2013) we have completed seven on farm-trials or campaigns where NH3 volatilization measurements were made following urea application to winter wheat for three application timings (late fall, winter and early spring). Each trial included two treatments; urea and NBPT-coated urea (Agrotain® coated urea) applied at 100 kg N ha-1. Losses of NH3 were quantified according to the protocol described in the proposal.  Cumulative NH3 losses for each trial (Table 1) are summarized in Table 1. Several conclusions have been evident from these cold weather application trials (summarized below).  


  • NH3 emission activity following surface-urea applications in the late fall and winter was often of modest intensity but prolonged in duration; cumulative N losses represented a sizeable fraction (10.6-20.7%) of the applied N application.  An example was provided by the results from Campaign 22 where volatilization resulted in a cumulative N loss of 19.3%.  This trial was conducted in a winter wheat field (Curtis Hershberger farmer-cooperator) near Denton, Montana and began with a fertilizer application to a cold soil (0.5 ?C) covered with patches of snow (Figure 4). NH3 fluxes over this campaign reached a maximum during the fourth week post-fertilization (26.6 g N ha-1) and did not fall to background levels until 106 days post-fertilization. The modest emission intensity and prolonged NH3 emission activity was a result of the cold temperature and dry conditions during this Montana winter that slowed urea hydrolysis rates.

  • NH3 emission fluxes were strongly related to evaporation. An example was provided by the photographs from Campaign 22 (Figures 6) showing the change in field conditions over a one week period. Winters in Montana are typified by light precipitation or snowfall events that result in modest snow accumulation, followed by periods of thaw or melting where the snowpack disappears.  During this period of snowpack melting and evaporation, the soil surface transitions from wet to dry, referred to as a wet to dry cycle, and NH3 emission activity from urea becomes elevated.

  • Cumulative losses of NH3 were lower for the early spring application compared to the late fall and winter applications because of the occurrence of large precipitation events following fertilization. For example in 2011-2012, a large spring precipitation event (25 mm) occurred over two to four days following fertilization during Campaign 21, resulting in only a 1.2% cumulative N loss. In 2012-2013, a total of 187 mm of precipitation was recorded over the 55 days during Campaign 24 resulting in only a 4.2% N loss.  Our performance target at the start of this study was to mitigate NH3 losses to ≤ 5% of the N input. The results of this study indicate that by delaying N applications to early spring we have a better chance of synchronizing N applications in front of large precipitation events (given typical precipitation patterns in MT), thereby enabling us to achieve this performance target.

  • Addition of NBPT or Agrotain® mitigated NH3 loss from urea by 63% (average of Campaigns 16, 18, 20, 22-24). The duration of NBPT protection was typically two weeks in acidic soils, but sometimes was considerably longer (>7 weeks) in alkaline soils. 

 Ammonia volatilization from pea green manure (Summer 2011 and 2012)

Field peas (Pisum sativum) are Montana’s most important alternate crop for diversifying dryland wheat rotations.   Inclusion of green manure peas in rotations provides N to the soil; however, legume termination at an immature growth stage has been reported to result in volatilization losses of NH3 which will diminish green manure fertility benefits as well as represent an important contribution of atmospheric NH3.

Field studies were conducted during the summer of 2011 and 2012 at private farms to learn whether termination of peas by mowing and herbicide spraying would lead to significant NH3 losses. Studies were established at a dryland field near Havre, Montana. In 2011, peas were terminated (July 6) by mowing (Figure 7) and herbicide spraying (2,4-D amine) at the early-pod stage. In 2011, peas were terminated by mowing only at the flowering stage. Field pea biomass at termination was equivalent to 3610 and 2780 kg dry matter ha-1 in 2011 and 2012, respectively. These pea biomass yields were average, to somewhat above normal, for this semiarid region. The N content in the biomass at termination was 105 and 79 kg N ha-1 in 2011 and 2012, respectively. Ammonia losses were measured over two weeks following termination. Cumulative NH3 losses from peas equated to 0.3 and 0.5% of the N in the above ground tissue for the 2011 and 2012 trials, respectively. These results indicated the fertilizer N value of field pea residue were not diminished as a result of NH3 volatilization, which represents good news to growers in the semiarid Great Plains concerned about N losses from NH3 volatilization following green manure termination.

Education Outreach Program

Pre-survey:  A 19-question hardcopy survey, or a link to the online survey, was sent to all members of the Montana Grain Growers Association, Wyoming Wheat Growers Association and Idaho Grain Producers Association in late fall 2010 to determine their current nitrogen management practices, knowledge of urea volatilization and preferred media for receiving research results.


  • A total of 147 surveys were returned.

  • Approximately 50% of applied urea is being broadcast without incorporation. 


  • The average estimate of urea volatilization loss was close to what we have measured (~22%), but the range was high (5 to 100%), suggesting room for education. 


  • Approximately 37% did not know the worst case weather conditions for urea application.



  • Respondents primarily preferred to receive results via email (27%), workshops (24%) or newsletters (17%). 


Scientific – refereed

Engel, R.E., C. Jones, and R. Wallander. 2013 Ammonia volatilization losses were small after mowing field peas in dry conditions. Can. J. Soil Sci. 93:239-242.

Engel, R.E., E. Williams, R. Wallander, and J. Hilmer. 2013. NBPT degradation occurs more slowly in alkaline soils. Soil Sci. Soc. Am. J. 77:1424–1429.

Engel, R., C. Jones, and R. Wallander. 2011. Ammonia volatilization from urea and mitigation by NBPT following surface application to cold soils. Soil Sci. Soc. Am. J. 75:2348–2357.


Jones, C., R. Engel, D. Horneck, and K. Olson-Rutz. 2012. Minimizing urea volatilization in cool semi-arid regions. Crops and Soils. 45(6): 28-32. (~15,000 readers).

Engel, R., C. Jones, and T. Jensen. 2012. Cold temperatures did not remove the risk of ammonia loss. Top Crop Manager – Western Edition. April 2012: page 28,30,36 (~27,000 readers).

Engel, R., C. Jones, and T. Jensen. 2012. Cold temperatures did not remove the risk of ammonia loss from surface-applied urea. Better Crops. Vol. 96 Issue 1: 9-11 (11,000+ readers).

Jones, C. 2011. Minimizing Volatilization of Surface-Applied Urea. Montana Grain News. December issue.   (~1575 readers).

Engel, R. and C. Jones. 2011.  Urea application on cold soils. Nutrient Digest. 1 (1):5-6. University of Idaho. (~2000 readers).

Press releases

Factors contributing to N volatilization and BMPs to minimize loss. MSU Press release March 2013.

University Extension

Jones, C., B. Brown, R. Engel, D. Horneck and K. Olson-Rutz. Management to Minimize Nitrogen Fertilizer Volatilization. MSU Extension. EB0209. 5 p. (available online http://landresources.montana.edu/soilfertility/PDFbyformat/publication%20pdfs/U%20vol%20BMP%20EB0209.pdf). 250 hardcopies delivered to date. The “American Society of Agronomy” awarded this publication the 2013 Extension and Education Community Award for Publications of < 16 pages.

Jones, C., B. Brown, R. Engel, D. Horneck and K. Olson-Rutz. Factors Affecting Nitrogen Fertilizer Volatilization. MSU Extension. EB0208. 6 p. (available online http://landresources.montana.edu/soilfertility/PDFbyformat/publication%20pdfs/U%20vol%20factors%20EB0208.pdf). 250 hardcopies delivered todate.

Engel, R. and C. Jones. 2012. Ammonia loss from urea surface-applied to cold soils. Montana Fertilizer Facts. Number 59. MSU Extension, Bozeman, MT. 2 pp. (available online http://landresources.montana.edu/FertilizerFacts/). 391 online visits according to Webtrends. 700 hardcopies delivered todate.

Engel, R. and C. Jones. 2012. Mitigation of ammonia loss from urea applied to moist soils by Agrotain. Montana Fertilizer Facts. Number 60. MSU Extension, Bozeman, MT. 2 pp. (available online http://landresources.montana.edu/FertilizerFacts/).  700 hardcopies delivered to date. 287 online visits according to Webtrends.


Abstract and Proceedings at Professional meetings (July 2010-present)

Engel*, R., C. Jones and R. Wallander. 2013. Improving fertilizer N recovery and mitigating NH3 volatilization from surface-urea applications in a semiarid climate. ASA-CSA-SSSA Conference Abstracts. Tampa, FL, November 3-6, 2013 (symposium, invited).

Engel, R.E., E. Williams, and R. Wallander. 2012. NBPT degradation and mitigation of ammonia loss from surface-applied urea in an acidic and alkaline soil. Great Plains Soil Fertility Conference, March 6-7, 2012. Denver, CO.

Engel, R.E., E. Williams, and R. Wallander. 2012. Degradation of the urease inhibitor N-(n butyl) thiophosphoric triamide) occurs more slowly in calcareous soils. 49th Annual Alberta Soil Science Workshop. Feb14-16, 2012. Edmonton, Alberta.

Engel, R. 2011. Volatilization losses from surface-applied urea during cold weather months. Manitoba Agronomist Conference, Dec 13-14, 2011. Winnipeg, Manitoba.

Jones, C., T. Rick, R. Engel, P. Miller, A. Moore, K.Olson-Rutz and S. Arnold. 2011. Comparison between online and hardcopy responses from a grower survey on urea volatilization. ASA-CSSA-SSSA 2011. International Annual Meetings. Oct 16-19, 2011. San Antonio, TX.

Engel, C. Jones, R. Wallander, T. Jensen. 2011. Cold weather volatility of NH3 from surface-applied urea: A micrometeorological study to quantify losses in the Northern Great Plains. 48th Annual Alberta Soil Science Workshop. Feb 15-17, 2011. Calgary, Alberta.

Engel, R.E. 2010. Cold weather volatility of ammonia from surface-applied urea: A micrometeorological study to quantify losses in the Northern Great Plains of America. Yangling Int. Agri-science Forum. Nov 1-3, 2010. Yangling, China. (invited)

Presentations to growers, commodity groups, ag-industry

Since the project’s inception (July 2010), we have presented the study findings 27 times to a range of audiences that included growers, crop advisers, Extension Agents and scientists (Table 2). Total direct contact at these presentations has totaled >1,200 people or >120% of our performance target of 1,000 direct contacts for the entire study. In addition, our research project was also mentioned at seven grower meetings in Idaho in February 2011, and at the Wyoming Wheat Growers Association annual meeting in December 2010.

Web-based materials

We have posted a streaming video of one of Dr. Jones’s presentations on urea volatilization on the ammonia volatilization portion of his website: http://landresources.montana.edu/soilfertility/ammonvolat.html.

We have updated the results from our studies with urea fertilizer at http://landresources.montana.edu/ureavolatilization – 1450 visits were recorded between May 1 and December 31, 2012 (updated numbers will be provided for 2013 in our final report).

Educational program evaluation plan

At our first two producer education programs in 2011, we asked audience members several questions to improve our programs.

  • The average attendee understanding increased from 2.75 (1 – poor, 5 – excellent) prior to the program to 4.02 after the program.
  • Approximately 80% of respondents said they would make a management change based on the presentation.
  • 100% said they would share the results with at least one other person.
  • Approximately 60 comments were received on how to make the educational program and research more worthwhile. We have incorporated some of these comments into our educational outreach plan and our research plans.
  • At our two presentations in July 2011 we used Turning Point’s clicker system to assess the worth of the program. The audience’s understanding of volatilization increased in 91 to 100% of respondents and 71 to 90% will make a management change based on our results.

Work left to do

Our micrometeorological field trials or campaigns are near completion. One trial is on-going following a December 1, 2013 fertilizer application, and two additional trials are planned for this winter and early spring. All trials are located on a private farm near Denton, Montana (Curtis Hershberger, farmer-cooperator) and are being coupled with a replicated small-plot fertility trials in order to quantify yield, protein and fertilizer N recovery at the request of Montana growers.  We will conduct a second survey in February-March 2014 targeting the same groups as for our pre-survey, to determine if management practices have changed as a result of this project. Recognizing that crop advisers and extension agents educate and influence management decisions on farms, we will also survey these groups.

Impacts and Contributions/Outcomes

Our ammonia volatilization project has garnered considerable interest and support by the agricultural community in Montana, in particular are the studies with urea. In 2011, we conducted grower surveys on the impact of our research on production practices. Evaluations from two seminars (i.e. Montana Grain Growers Association Convention and Nitrogen Conference) indicated that 80% of the respondents will likely change a management practice based on what they learned at the seminar, and 100% of the respondents said they will share what they have learned with at least one other person. As described in our proposal, outcomes and impacts of this project will be gauged from the results of surveys, as well as the personal contact hours accumulated over the course of this study. The results of our surveys, evaluations and discussions with growers indicate this project is having a large impact on growers in this region. There are several reasons why this may be so. First, the information presented is relevant to management practices in the region (i.e. 50% of our survey respondents say they applied urea without incorporation). Second, nitrogen fertility and nitrogen inputs typically represent a grower’s largest annual cost input. Third, nitrogen is the fertilizer nutrient most often limiting crop yield and quality in NGP cropping systems. Therefore, management of this input to maximum crop efficiency is important to a grower’s bottom line as well as environmental quality. Most importantly, several growers and crop advisers have told us that they have changed, or plan to change, their urea management practices to minimize volatilization. This has likely increased their grain yield, grain protein and net revenue.


Dr. Jay Norton
Project Cooperator/Assist. Prof Soil Fertilty
University of Wyoming
Department of Renewable Resources
1000 E. University Avenue
Laramie, WY 8207-3354
Office Phone: 3077665082

Neil McCormick
44 Road 305 S
Havre, MT 59501
Office Phone: 4063723162

Curtis Hershberger
801 N Bain Street
Denton, MT 59430
Office Phone: 4068999310

Dr. Perry Miller
co-PI/Cropping System Specialist
Montana State University
Dept. of Land Resources and Environmental Sci.
Leon Johnson Hall
Bozeman, MT 5971-3120
Office Phone: 4069945431

Dr. Clain Jones
co-PI/ Montana Extension Soil Specialist
Montana State University
Dept. of Land Resources and Environmental Sci.
Leon Johnson Hall
Bozeman, MT 5971-3120
Office Phone: 4069946076

Dr. Amber Moore
Project Cooperator/Idaho Extension Soils Specialist
University of Idaho - Twin Falls Research and Extension Center
315 Falls Avenue, Evergreen Bldg
P.O. Box 1827
Twin Falls, ID 8330-1827
Office Phone: 2087363629

Les Kaercher
40682 US Highway 2
Havre, MT 5950-8225
Office Phone: 4062653161

Mark Peterson
18586 Road 325 N
Havre, MT 5950-8044
Office Phone: 4063942216