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

View the project final report

• 2011 annual report
• 2012 annual report
• 2013 annual report

Commodities

• Agronomic: hay, wheat

Practices

• Animal Production: feed/forage
• Crop Production: conservation tillage
• Education and Training: demonstration, extension, farmer to farmer, on-farm/ranch research, participatory research, workshop
• Farm Business Management: budgets/cost and returns
• Soil Management: green manures, soil analysis

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.

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.