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

2012 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 NH losses from these sources have rarely been conducted. This Research and Education 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 between fall to early spring. Two or three different application timing dates will be compared at each farm site, e.g. October, December-January and March-April. We have conducted preliminary studies that indicate losses can be quite large from cold soils (up to 40%). 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 is 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 is 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 educational 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.


Field studies have been conducted at eight locations since this project’s inception according to the protocol described in the proposal. These field studies conducted to date 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 is the accumulated contact hours with producers in our region. Currently, we have accumulated 990 contacts or 99% of our final target. A brief summary of our research results and educational outreach program is provided below.

Research Results

Preplant 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 experiments were conducted at four no-till wheat farm sites (Campaigns 13, 14, 15 and 17) in northern Montana during fall 2010 and fall 2011, 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 reveal 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 occurs under dry conditions, soil disturbance is low and most of urea prills remain visible at the surface (Figure 2). If the soil is moist at the time of seeding the surface the level of disturbance is greater and a higher percentage of fertilizer prills are covered with soil.

Ammonia losses are summarized in Figure 3 for the four campaigns conducted over the past 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. To date, there has been no evidence that disturbance created by air seeders is 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). These conditions are common for growers in Montana as precipitation during the late-summer and early- fall is often low. Precipitation amounts and patterns following seeding have a large impact on the size and distribution of NH3 losses. Previous 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 0.60 cm and 1.52 cm fell one day and five days 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 1 and 2. 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 0.77 cm 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 snow (winter 2011 and 2012)

Growers in Montana frequently surface-apply urea during the winter. 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 frozen soils. This question is being addressed in our study.

In 2011 and 2012, we conducted NH3 volatilization measurements following urea application to a field sites with a modest or intermittent snow-pack (Figure 5-left and 6-left). The study included two treatments; urea and NBPT-coated urea (or Agrotain coated urea) applied at 100 kg N ha-1 and was run according to the protocols described in the proposal. Results of the trial (Campaign 16) are summarized in Figure 7. In 2011, cumulative NH3 losses from urea were equivalent to 20.7% of the application rate (100 kg N ha-1) over an eight-week period. Losses were particularly large during the second week (7-14 days post-fertilization) when the snow-pack disappeared (see Figure 5 – right) and the surface soil conditions followed a wet to dry cycle. Coating urea with Agrotain provided approximately two weeks of volatility protection and reduced NH3 losses by approximately 50% over untreated urea. In 2012, cumulative losses from urea were equivalent to 13.0% of the application rate over an eight-week period.

Ammonia losses were lower in 2012 compared to 2011. The amount of water in the snow in 2012 was not as great as in 2011; hence after the snow melted the surface was not as wet and the loss in water during dry down as not as great. In 2012, coating urea with Agrotain reduced NH3 losses by approximately 68.5% over untreated urea. The duration of volatility protection from Agrotain was greater in 2012. Soil pH may play a role in this response. The active ingredient in Agrotain, N-(n-butyl) thiophosphoric triamide (NBPT), is known to breakdown more slowly in alkaline compared to acidic soils, and the soil pH at Campaign 16 and 20 was 6.9 and 7.5, respectively.

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, their termination at an immature growth stage has been reported to result in volatilization losses of NH3, which will diminish their fertility benefits as well as represent an important contribution of atmospheric NH3.

Field studies were conducted during summer 2011 and summer 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 8) 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 average to somewhat above norm 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 suggest the fertilizer N value of field pea residue will not be diminished appreciably as a result of NH3 volatilization, at least during the two weeks following termination. The results of this study could represent good news to growers in the semiarid Great Plains who are concerned about N losses from NH3 volatilization following green manure termination.

Education outreach program – 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%).

Education outreach program – 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. (in review).

Engel, R.E., E. Williams, R. Wallander, and J. Hilmer. 2013. NBPT degradation occurs more slowly in alkaline soils. Soil Sci. Soc. Am. J (in review).

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)

University Extension

Montana Fertilizer Fact articles (below) are available on-line and in hard copy.(http://landresources.montana.edu/FertilizerFacts/)

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. 391 online visits according to Webtrends. 700 hardcopies delivered.

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. 287 online visits according to Webtrends. 700 hardcopies delivered.

We are in the final stages of editing our regional Extension publication, “Management of urea to minimize volatilization” (Jones et al., 2007) to reflect our research findings. The updated version will be broken into two documents, tentative titles “Factors that affect volatilization” and “Best management practices to minimize volatilization.” We expect to have both published by April 2013.

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

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)

Education outreach program – Presentation

• Presentations to growers, commodity groups, ag-industry

Since the project’s inception (July 2010), we have presented the study findings 18 times to a range of audiences that included growers, crop advisers, Extension Agents and scientists (Table 1). Total direct contact at these presentations has totaled approximately 990 people or 99% of our performance target of 1,000 direct contacts for the entire study.

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 – 1,450 visits were recorded between May and December 31, 2012 (note – the number of visits to this web site was tracked beginning in May)

• 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

We have been asked by growers to better understand the impact of NH3 loss from urea on income reductions as a result of yield or protein reductions. To address this issue we are now coupling our micrometeorological measurement of NH3 loss from urea with replicated small-plot fertility trials in order to quantify yield, protein and fertilizer N recovery. These studies are being conducted at a field site near Denton, Montana and with the cooperation of a grower (Curtis Hershberger). This work is anticipated to last through summer 2014. Our studies with green manure have been submitted to the Canadian Journal of Soil Science and are currently in review (Engel et al. 2013 – Title: Ammonia volatilization losses were small after mowing field peas in dry conditions). The initial reviews have come back and suggest that we may want to run NH3 loss measurements following green manure termination over a longer time than our current two week time-scale.

We will conduct a second survey next winter targeting the same groups as for our pre-survey to determine if management practices have changed as a result of this project. As mentioned earlier, we are updating our Extension Bulletin and will publish two Extension Bulletins on the topic soon, partly based on results from this study.

Impacts and Contributions/Outcomes

Our ammonia volatilization has garnered considerable interest and support by the agricultural community in Montana, in particular our 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 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