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

Final 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
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Project Information


Globally, ammonia (NH3)loss to the atmosphere from agriculture (fertilizer and manure) represents a significant pollution source, accounting for 50% of global emissions. Elevated atmospheric NH3 can lead to formation of fine particulates, a major source of haze that reduces visibility. Further its deposition into natural, undisturbed ecosystems that are typically nutrient poor can to lead to changes in plant communities, soil acidification and eutrophication of natural waters. In addition, because N is the primary nutrient limiting crop growth, NH3 loss to the environment represents a potential economic loss to farmers as a result of N deficiency and reduced crop yield and quality.

This project was conducted to quantify on-farm NH3 losses from legume green manure and fertilizer inputs in Montana, identify environmental and soil conditions conducive to large NH3 losses, define management strategies to mitigate losses and communicate the results to producers and agricultural professionals. The emphasis for our fertilizer studies was urea, because it represents 86% of the fertilizer N consumption in the state and is often broadcast applied to the soil surface in no-till systems that dominate Montana dryland cropping systems.

Field trials were conducted on private farms under long-term no-till management in north and central Montana. In 2011 and 2012, trials conducted with field peas (Pisum sativum L.) revealed that termination of this crop by mowing or with herbicides resulted in only nominal NH3 losses equivalent to only 0.3 to 0.5% of the N in plant biomass and indicating that N fertility was not diminished appreciably following legume termination. A urea application timing trial was conducted over three seasons in central Montana and revealed that cumulative NH3 losses averaged 16.3, 11.4 and 1.9% for applications (100 kg N ha-1) in the late-fall, mid-winter and spring. The lower NH3 loss for the spring applications was attributed to the greater frequency of large precipitation events that resulted in urea infiltration in the soil where it is protected against volatility. Conversely, applications in the late-fall and winter to cold frozen soils were typically followed by light precipitation events, and as a result, urea remained at, or near, the surface for an extended period of time. Under these conditions, urea hydrolysis occurred slowly as a result of cold temperatures and limited water, and although NH3 fluxes were low in intensity, they were prolonged, lasting 80 to 100 d post-application.

Several strategies to mitigate NH3 loss from urea were tested with varying results. Addition of the urease inhibitor, NBPT or Agrotain®, produced consistent results and reduced cumulative NH3 losses by 64% over untreated urea. Four field trials were conducted to determine if surface applying urea in advance of seeding would mitigate NH3 loss. Interest in this strategy came as a result of communication with growers at meetings where they asked if the disturbance created by their air-seeders configured with hoe-style openers was sufficient to cover urea prills on the soil surface and thereby mitigate NH3 loss. The results of these tests were negative, meaning there was no significant difference in NH3 losses between applying urea pre- or post-seeding. Growers also asked whether urea applications onto snow would result in nominal NH3 losses. This mitigation strategy was evaluated in the winter of 2011 at a field site in central Montana. Urea was broadcast onto a field with a modest snowpack (0.9 cm water equivalent). Cumulative NH3 loss from urea was found to be equivalent to 21% of the N application (100 kg N ha-1) over an eight week period, invalidating this mitigation approach. Results from this last trial and other trials indicate that NH3 emissions in the winter were typically most intense during thaw-periods, when the snowpack disappears and/or the soil transitions from wet to dry (referred to as “wet to dry cycle”).

This study conducted an active education and outreach program to producers and agricultural professionals that produced three refereed publications, seven abstracts and proceedings, four MSU extension publications, two ag-industry articles, one press release, a web site and 33 oral presentations to a diverse audience that included growers, commodity groups, ag-industry reps and scientists. We were successful in reaching (and exceeding) our performance target of 1,000 people-hours and indirect contact with another 5,000 people through radio, news releases, ag-professional training and farmer to farmer communication. The impact of our results with producers was evaluated through online surveys (MT) and the surveys at the conclusions of meetings (ID and MT).  The results show that approximately 50% of MT and 12% of ID growers made changes to their N managements in response to information presented from this study. The economic impact of these changes to Montana either through reduced fertilizer N loss or greater net revenue from higher wheat yield or protein was found to be approximately $5 million annually. However, because we disseminated our results nationally with a focus in the West, the actual savings would likely be greater.

Project Objectives:

i.   To quantify on-farm ammonia loss from urea fertilizer applications (chemical) and legume termination (biological) from NGP dryland cropping systems. Our performance target was to determine the fraction of applied urea fertilizer lost as NH3 for applications to winter wheat applied from late-fall to early spring. Our study sought to identify the environmental and soil conditions that were most conducive to high NH3 losses. Our second performance target was to determine the fraction of N in legume manure lost as NH3 following its termination by mowing and/or glyphosate spraying.

ii. Identify mitigation strategies or production practices that minimize ammonia-N losses where losses were found to be significant from inorganic and organic N inputs. Our performance target was to mitigate NH3 losses to ≤ 5% of the N input.

iii. 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 was to achieve direct contact with 1,000 people (or people-hours) and indirect contact with another 5,000 people through radio, news releases, ag-professional training and farmer to farmer communication. Our education program targeted ag-professionals as they were involved in outreach to their grower clients. Therefore we anticipated a multiplier effect to our direct contact hours outreach program to producers and agricultural professionals that have, and will, improve their understanding of on-farm N cycles and N loss mitigation.


Ammonia (NH3) volatilization is a significant pathway of N loss from agricultural systems accounting for 50% of global emissions (Schlesinger and Hartley, 1992). Elevated atmospheric NH3 may pollute surface waters and contribute to loss of diversity in natural ecosystems. In addition, NH3 losses reduce economic sustainability when N that would otherwise be utilized by crops is lost to the environment.  Farmers in Montana and neighboring states are likely experiencing significant N losses as NH3 from chemical or biological inputs without their knowledge. One example is provided by N fertilization programs currently being practiced on Montana farms. Montana family farms are characterized by large acreage, no-till or minimal disturbance management, and wheat or related grains as the primary incoming producing crop. Optimum winter wheat seeding in the NGP occurs over a short time window, resulting in considerable time constraints on individual farmers who often seed 1,500 to 2,000+ acres. Although most modern air-drills are capable of injecting N fertilizer below the soil surface where it is less susceptible to volatilization, this practice is often not performed as it is slows seeding operations down. Therefore, most growers defer N fertilization until late-fall to early spring when urea (46-0-0) is typically surface broadcast. The rationale for this management decision is based on the desire to expedite seeding operations, and the belief that NH3 volatilization is not problematic if urea is applied to cold soils. In 2008, a micrometeorological study conducted in Montana found substantial volatilization losses (up to 40%) can occur even when urea is applied to cold soils (~0? C), thereby contradicting these long-held beliefs and impacting sustainability of no till in the NGP (Engelet al., 2011).

Although NH3 volatilization from chemical fertilizer is a significant path of N loss, few on-farm studies using a micrometeorological approach (SARE database, Nat. Agric. Library, USDA-CRIS) have been conducted in Montana and semiarid climates in the West.  Also, many N fertilizer studies focus on losses that occur under warm temperatures (> 50 F). In Montana, N fertilizer is rarely applied under these warmer conditions, but rather during cold weather months. Similarly, only a few studies have looked directly at NH3 losses associated with legume green manure termination or decomposition. Legume green manures, often promoted as an N fertilizer source in diversified production systems. Previous research has indicated that volatilization losses of NH3 from decomposing green manure may appreciably diminish its fertility benefit and represent an important contribution to atmospheric N (Janzen et al., 1991). As an example, a study in Sweden found volatilization losses of NH3 from alfalfa and high-N grass mulch were equivalent to 17% and 39% of the assimilated plant N (Larsson et al., 1998). In addition, grain N following legume green manures has been found to be higher after tillage than after chemical termination, especially at low N rates, suggesting higher N loss from chemical termination (Burgess et al., 2014).

The proposed study utilized a mass-balance micrometeorological approach referred to as the integrated horizontal flux method to quantify NH3 emissions associated with urea fertilization (chemical) and legume green manure termination (biological).  Studies were conducted at dryland farms in northern and central Montana and provided new knowledge to alert growers about NH3 loss from their fields and to inform them of management strategies that minimize these losses.  The proposed research and education project seeks to expand upon this existing work recently initiated in this region (http://landresources.montana.edu/ureavolatilization/) and to provide outreach and education to the agricultural community, including farmers and agricultural professionals. 


Burgess, M., P. Miller, C. Jones, A. Bekkerman, 2014. Tillage of cover crops affects soil water, nitrogen, and wheat yield components. Agron. J. 106:1497-1508.

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.

Janzen, H.H. and S.M. McGin. 1991. Volatilize loss of nitrogen during decomposition of legume green manure. Soil Biol. Biochem. 23:291-297.

Larsson et al., 2008 Ammonia and nitrous oxide emissions from grass and alfalfa mulches. Nutr. Cycl. Agroecosys. 51:41-46.

Schlesinger, W.H. and A.E. Hartley. 1992.  A global budget for atmospheric NH3. Biogeochem.15:191–211.


Click linked name(s) to expand
  • Curtis Hershberger
  • Dr. Clain Jones
  • Les Kaercher
  • Neil McCormick
  • Dr. Perry Miller
  • Dr. Amber Moore
  • Dr. Jay Norton
  • Mark Peterson


Materials and methods:

Field trials were established at private farms in Hill and Fergus County, Montana over four seasons in support of Objectives i and ii. All trials were conducted in fields under no-till management. Ammonia gas loss measurements were quantified according to the integrated horizontal flux method using circular plots (20 m radius) and a center mast equipped with five or six NH3 Leuning samplers (traps). Details on the mast and shuttle design, NH3 loss calculations, corrections for atmospheric background NH3, shuttle elution and chemical analysis of NH3 can be found at http://landresources.montana.edu/ureavolatilization. The design of many of our field trials was done with the participation and input from growers and consistent with SARE’s respect for agricultural producers. The trials included the following experiments. 

  • Two field trials conducted in northern Montana (Hill County) in 2011 and 2012 focused on NH3 loss following termination of field peas (Pisum sativum L.) by mowing or with herbicides (2011 only). 

  • Growers in Montana frequently surface-apply urea during cold weather months, and growers have wondered whether NH3 losses from urea could be mitigated if applications were made to cold soils during the winter. In addition, the use of NBPT or Agrotain® has been promoted by the fertilizer industry as a way to mitigate NH3 loss from urea. To address these questions, we conducted a cold weather urea and urea+ N-butyl thiosphoric triamide (NBPT) application timing experiment over three seasons (2011-2012, 2012-2013 and 2013-2014) in central Montana (Fergus County). The timings included a late-fall application at freeze-up, a mid-winter application in February and a spring application in April. The three urea timings were included in order to cover the time window (late-fall to spring) when most urea applications are made to winter wheat in Montana. At each timing, urea was surface-applied at (100 kg N ha-1) without and with NBPT (0.1%) or Agrotain®. NBPT is a urease inhibitor that reduces the rate of urea hydrolysis in the soil, thereby inhibiting NH3 loss and was included in order to quantify the potential of this product to mitigate NH3 loss. 

  • A pre-plant urea application timing experiment was conducted at four field sites in northern Montana (Hill County) during the fall of 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 meetings, growers asked if the disturbance created by their air-seeders configured with hoe-style openers was sufficient to cover urea granules on the soil surface, thereby mitigating NH3 losses. Urea was applied as a pre-plant (< two hours prior of seeding) and post-plant (< two hours following seeding) at a rate of 100 kg N ha-1. The post-plant urea treatment was included as a positive control to assess the potential for NH3 loss from urea without incorporation. 

  • The final mitigation strategy tested was to apply urea onto snow. This mitigation approach was tested at a field site in central Montana (Fergus County) in the winter of 2011 as we were asked by growers if NH3 loss from urea could be prevented if applications were made onto a snowpack. 

Our education and outreach program consisted of scientific articles, proceedings at regional meetings, producer directed publications and oral presentations to diverse audience groups. Grower surveys (pre-study and post-study) were conducted near the beginning (December 2011) and end of this study (March-July 2014) in support of Objective iii (see attachments). The surveys were conducted to identify more clearly grower N management and cropping practices and knowledge of conditions that are conducive to fertilizer N volatilization losses.  Surveys were approved by MSU’s Institutional Review Board prior to delivery. The pre-study survey was emailed to all Montana Grain Growers Association (MGGA) members who provided email addresses (n=~700) and a hardcopy mailed to the remainder (n=~300). It was also handed out at several workshops in Montana, Idaho and Wyoming. Numbers completing the survey were 86, 47 and 7 for MT, ID and WY, respectively. The area farmed by those respondents totaled 540,000 acres. The post-study online survey was emailed to all MGGA members with email addresses (vast majority) and was advertised in an MSU press release, the Montana Conservationist (June), and the Montana Grain News (July edition). A total of 75 producers responded, representing 240,000 acres. In addition, a post-study survey (four questions) was conducted at two oral presentations in Montana and five presentations in Idaho, with 31 and 230 respondents, respectively.

Research results and discussion:

Ammonia volatilization following termination of field peas

The results of this trial are summarized in the Canadian Journal of Soil Science (Engel et al. 2013. Ammonia volatilization losses were small after mowing field peas in dry conditions.  Can. J. Soil Sci. 93:239-242).  In 2011, peas were terminated (July 6) by mowing (Figure 1) 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 3,610 and 2,780 kg dry matter ha-1 in 2011 and 2012, respectively. These pea biomass yields were 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 loss from peas was equivalent to 0.3 and 0.5% of the N in the above-ground tissue for the 2011 and 2012 trials, respectively. These results indicated no reduction in the fertilizer N value of field pea residue as a result of NH3 volatilization, at least for the two weeks following termination. Peas were terminated by mowing in this study, which was very destructive to plant tissue and left the residue on the soil surface exposed to the atmosphere. The level of disturbance likely equals, or exceeded, what might be expected from tillage by a farm implement. Hence, we would expect NH3 loss to be nominal from peas terminated by tillage under similar environmental conditions. Also, tillage will bury a portion of the green manure residue, which should further mitigate NH3 emissions to the air, as has been reported in the literature. The results of this study represent good news to growers in the semiarid Great Plains who are concerned about N losses from NH3 volatilization following green manure termination.

Surface-urea applications timing during cold weather months

Cumulative NH3 losses for the three growing seasons are summarized in Table 1.  A summary of the results and conclusions is provided below. 

  1. Cumulative NH3 loses from urea were greater for late-fall (16.3% of applied N) and mid-winter (11.4% of applied N) than spring applications (1.9 % of applied N). Ammonia emission activity following the late-fall and mid-winter was often of modest intensity but prolonged in duration. An example was provided by the NH3 flux vs. time relationships for the late-fall applications (Figure 2). Maximum NH3 fluxes were observed between 14 and 28 d post-fertilization and ranged from 18.3 to 26.6 g N ha-1 hr-1. This equates to 3.1 to 4.5 kg N ha-1 per week. The modest emission intensity and prolonged NH3 emission activity was a result of the cold temperature and dry conditions during Montana winters that slowed urea hydrolysis rates. Soil temperatures during the winter were typically near or below 0 ?C and sometimes covered by modest snow-pack, but periods of intermittent thaw created snow-free conditions. Emissions did not permanently fall to < 1 g ha-1 hr-1 until 103 and 130 d post-fertilization in 2012-2013 and 2013-2014, respectively. Ammonia emission measurements in 2011-2013 never fell to < 1 g ha-1 hr-1 after 87 d. It is possible our NH3 loss measurements would have been somewhat higher had the gas sampling campaign been continued.

  2. Elevated NH3 emission fluxes were strongly related to evaporation, i.e. fluxes rose as evaporation increased. An example was provided by the photographs from trials conducted in 2011-2013 (late-fall application) (Figure 3) showing the change in field conditions over a one week period. Winters in Montana are typified by light 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.

  3. Cumulative losses of NH3 were lower for the early-spring application compared to the late-fall and winter applications because of the occurrence of more frequent and intense precipitation events following fertilization.   For example, in 2011-2012, a large spring precipitation event (25 mm) occurred over 2-4 d following fertilization, resulting in only a 1.2% cumulative N loss. In 2012-2013, a total of 187 mm of precipitation was recorded over the 55 d following fertilization and resulted in only a 4.2% N loss; and in 2013-2014 17 mm of precipitation was received over the first two week post-fertilization, resulting in less than 1% 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 advance of large precipitation events that are more common in the spring compared to the winter and reducing N losses to less than 5% of the N input.

  4. Addition of NBPT or Agrotain® reduced NH3 loss from urea by 64% (average of early and mid-winter trials), thereby validating its efficacy to mitigate NH3 loss. Coating urea with Agrotain® cost approximately $55 per ton of fertilizer. Assuming urea cost $500 per ton, this represents an 11% added cost which would need to be recovered through increase wheat yield or protein or in reduced N fertilizer application in order to justify its use.

Pre-plant urea application timing experiments to mitigate ammonia loss 

Results from the four trials comparing pre-plant vs. post-plant urea applications are summarized in Table 2. Cumulative NH3 loss averaged 14.0 and 12.8% of applied N for the pre- and post-plant applications, respectively. A paired t-test indicated there was no significant difference between the treatments (P=0.64), indicating the soil disturbance created by air-drills seeders was not sufficient to mitigate NH3 loss. In two trials (Trial 3 and 4), seeding was done into soil which was extremely dry (< 5% moisture by weight) near the surface, such that dust clouds were created behind the seeder (Figure 4a). The disturbance level created by the air-drills at these sites was nominal and urea granules were still visible at the surface (Figure 4 b,c).  In contrast, the surface soil layer at Trials 1 and 2 contained 15.0 and 12.6% moisture and the air-drill created somewhat more disturbance at these sites. Although many of urea granules were not visible, no reduction in NH3 loss was observed. Overall, NH3 losses were lower at Trials 3 and 4 relative to Trials 1 and 2 because of dry soil conditions at seeding and minimal rainfall amounts following seeding. These conditions likely limited urea hydrolysis. Precipitation totaled only 7.7 and 19.2 mm over the first seven weeks post-fertilization at Trials 3 and 4, respectively. A large percentage of the applied urea likely never hydrolyzed during Trial 3 because of drought conditions.

Research conclusions:

The results of this study and previous research indicate that NH3 losses from surface-applied urea can be mitigated by: 

  1. Timing urea applications that are applied to dry soil surfaces and in advance of large precipitation events. In Montana, large precipitation events are more common in the spring compared to winter. Hence, spring applications are likely to see lower NH3 losses compared to winter applications. At least 13 mm of precipitation (0.5”) in a single event is needed to move urea into the soil deep enough to prevent volatilization. Light scattered rain is often not sufficient moisture; it may increase rather than prevent volatilization losses.

  2. Avoiding urea applications to when the soil surface is wet or damp and/or snow-covered. Large losses of NH3 can occur under these conditions (up to 22% of applied N can be lost in one week), particularly if the applications to wet surfaces are followed by period of drying with little or no precipitation.

  3. Utilizing urease inhibitors such as Agrotain®. Our field tests with Agrotain® indicate that NH3 volatilization losses are mitigated by approximately 64%.

  4. Applying urea in a subsurface band.  Although we did not specifically test this strategy during this study, we have promoted this approach during our Education and Outreach programs because NH3 losses from urea are known to be eliminated by placement of urea granules below the soil surface.

These recommendations were communicated to the Montana ag community at grower meetings and oral presentations over the course of this study. Their impact on grower production practices was evaluated in a post-study survey. Growers were asked if they adjusted management practices based on the results of our study. In Montana, results from the online survey found that 30% of the growers now adjust for weather, 18% now use an enhanced efficiency fertilizer such as Agrotain? and 25% now subsurface band (Figure 7). About 12% had not made any changes yet, and 16% were already using these practices prior to the study.  Only 13% of the respondents were not aware of our study. Clicker respondents (of those who changed practices) at oral presentations in Sidney and Malta found that 48% began using enhanced efficiency fertilizer products, 35% now consider weather by applying urea on dry soil or before rainfall and 12% now apply urea in a subsurface band. Combined survey and clicker responses from Montana indicated that because of this Western SARE funded research, 22% started considering weather more, 16% began using an enhanced product and 16% began subsurface banding. The increase in the number of people who subsurface band N at seeding is particular significant, because injecting N below the soil surface will eliminate NH3 volatility losses.  Our survey found 42% of our respondents now apply the majority of their N fertilizer in a subsurface band (Figure 8). This survey is indicative of the entire state as it now represents the primary approach for N management, followed by spring broadcast applications timings (39%) which we have found to be the least susceptible to NH3 volatility of different broadcast timings.

Post-survey responses from Idaho were very different, where fully 77% were not aware of the research, and only 13% were both aware of the research and had made changes (31% subsurface banded or incorporated was most frequent management change). The differences between states is likely a result of a much more targeted outreach campaign (detailed elsewhere) in Montana than in Idaho (or Wyoming). There is also a much higher percentage of dryland cropping and, hence, unincorporated urea broadcast applications in MT than in ID, so interest in MT is higher.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

Publications 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.

Abstract and Proceedings at Professional meetings

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)  


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).

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.  250 hardcopies delivered. Available online at http://landresources.montana.edu/soilfertility/PDFbyformat/publication%20pdfs/U%20vol%20BMP%20EB0209.pdf). 

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

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. 700 hardcopies delivered and available online at http://landresources.montana.edu/FertilizerFacts/

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. 700 hardcopies delivered and available online at http://landresources.montana.edu/FertilizerFacts/.

Presentations to Growers, Commodity Groups, Ag-Industryand Scientific

Since the project’s inception (July 2010), we have presented the study findings 33 times to a range of audiences that included growers, crop advisers, Extension Agents and scientists (Table 4). Total direct contact at these presentations has totaled approximately 1,400 people or 140% 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, five ID grower meetings in 2014 and at the Wyoming Wheat Growers Association annual meeting in December 2010.

Project Outcomes

Project outcomes:

Annual economic impacts were analyzed with two different methods: 1) fertilizer N savings ($) from mitigation of NH3 loss and 2) increased gross revenue ($) from increased wheat grain yield and protein due to adoption of a best management practice (BMP). Most of the inputs for this analysis came from the surveys and some were estimated. Dr. Jones’s yield, protein and net revenue models (based on decades of Montana soil feritlity trials) were used to estimate net revenue increases from the projected reduced losses (see http://landresources.montana.edu/soilfertility/small%20grains%20economic%20calculator.html). The estimates were only made for Montana because altered practices were low in ID (~13%), and we had insufficient information to conduct this analysis. Broadcast N rate was calculated as N application rate x fraction of N broadcast. Equations for each strategy are defined below and a list of parameters and their values are provided in Table 3.   

1. NH3 loss mitigation with BMP adoption (e.g. NBPT, considering weather, subsurface band = (mean broadcast N application rate, lbs N/acre)  x 

(acres of wheat)  x 

(% growers adopting new practice)/100  x 

(reduction in N loss with BMP)


Total N fertilizer loss mitigation (dollars) =

sum of NH3 loss mitigation for the three BMPs (or NPBT, weather, subsurface band) x

urea cost ($/lb)


2.  Increased gross revenue ($) was calculated from the estimated difference in winter + spring wheat net revenue with  the adoption of BMPs.

Available N pre-study = Avail N/bu x yield goal – (broadcast N rate – broadcast N rate x fraction volatilized w/o mitigation)

Available N post-study = Avail N/bu x yield goal – (broadcast N rate – broadcast N rate x fraction volatilized w/mitigation for each practice)

Gross revenue savings = sum of (net revenue w/ pre-study available N – net revenue w/ post-study available N) x acres with adopted new practice

The savings for the two approaches were almost identical averaging approximately $5 million per year for the state of Montana. This estimate is likely conservative for the United States because we disseminated our results nationally with a focus in the West.  Also, output from Dr. Jones’s economic model shows a modest 0.2% boost in protein with the application of BMPs to reduce NH3 volatilization. We have conducted a limited number of replicated small-plot trials in grower’s fields to directly measure this effect. To date, our results have shown that deferring N application to early spring (reduced volatilization loss potential) will boost grain protein 0.5 to 1.5% over late-fall and winter applications (when volatilization loss potential is high) and addition of NBPT or Agrotain? to urea will boost grain protein 0.5 to 0.8% over untreated urea. 

Farmer Adoption

This project, in particular our studies with urea, has garnered considerable interest and support by the agricultural community in Montana and neighboring states. Over the past four years we have conducted formal surveys of growers to gauge producer attitudes about this project and its results. The results indicate that a majority of Montana producers have altered, or plan to alter, their management practices to minimize volatilization. Adoption in Idaho has been much lower; only 12% of 230 growers at talks earlier in 2014 knew about the research and had altered practices. Though now all of those 230 growers know about the research and the take home messages, so adoption may increase in ID as well. 

Anecdotal evidence from our numerous contact hours with growers has always demonstrated to us that producers have adopted changes to their management practices. For example, we know of several growers who now apply all their urea N in a subsurface band as seeding, rather than surface apply urea during cold weather months. Crop advisers tell us they now pay far more attention to weather and target more spring time applications or enhanced efficiency fertilizer products.

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. 


Areas needing additional study

In the future we would like to investigate ammonia losses from other N sources, e.g. UAN and/or ammonium sulfate.  Also, the fertilizer industry is developing and releasing new urease inhibitors  that should provide protection from volatilization losses and which should be tested in the field. Finally, the impact of ammonia N losses on production and quality, fertilizer N recovery and nitrogen used efficiency in crops is not well defined and is of concern to many farmers.  We made some attempts to address this issue in this project, but additional investigations should be conducted.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.