Options to Reduce Greenhouse Gas Emissions in Production Agriculture

By Michael Reese, Director of Renewable Energy

November 2020

Scientists world-wide are working on solutions to reverse the current trend of global climate change.  Production agriculture is estimated to be responsible for approximately 25% or a quarter of global greenhouse gas emissions (IPCC, 2017).  There are many questions regarding the proper path leading to reduced greenhouse gas emissions in production agriculture.  One popular approach is to change the manner in which land is used.  Examples of the land use approach are implementation of cover crops, no-till and reduced tillage, moving away from corn and soybean rotations to perennial grains such as crested wheatgrass, or simply returning working lands back to native grasslands.  Even though these approaches have potential to reduce greenhouse gas emission, each one can be very disruptive for Minnesota farmers.  Cover crops have been implemented with some success and federal farm programs have offered financial assistance for this practice so this is a low hanging fruit.  No-till and minimum tillage requires investment in different equipment which can be costly for producers and, yields have been shown to be reduced using these methods especially for corn production.  Switching to perennial crops, although promising, require new mechanisms to market these grains and oilseeds.  The markets for new grains and oils seeds are volatile and there are limited options for managing risks such as crop insurance.  In addition, the new crops may also require changing equipment lines.  And, removing production agriculture lands from productions and returning to native grasslands requires significant public investment to displace the lost farm income.  Converting to grasslands has an added disadvantage of reducing US agriculture production which has global economic, food security, and supply considerations.      

At the WCROC, we have been collecting energy data and evaluating results from our cropping and livestock operations.  The pie graph below indicates the fossil energy footprint for corn production at the WCROC (courtesy of Joel Tallaksen, 2016).

Fossil energy footprint for corn production

From the graph, approximately 36% of the energy footprint from corn production is attributed to nitrogen fertilizer and 42% is due to grain drying.  If we were to replace the fossil-based nitrogen fertilizer with green ammonia from the wind-to-ammonia pilot plant and were to use the same green ammonia as a fuel for the grain drying operation, 78% of the fossil energy footprint could be removed. (Incidentally, there is a sponsored project underway with the Department of Mechanical Engineering to test fueling the WCROC grain dryer with green ammonia.)  By converting tractors and grain trucks to be fueled by green ammonia (as demonstrated in the summer of 2019 with the ammonia-fueled tractor), we could achieve a 93% reduction in fossil energy within corn production.  This is transformational on many levels and establishes a clear path towards decarbonizing corn production.  Now with that said, converting tractors and trucks to use green ammonia as a fuel is also very disruptive and requires significant investments and modifications.  However, green ammonia can directly replace brown ammonia for nitrogen fertilizer since they are the same (green made from renewable energy and brown made from natural gas or coal gasification).  In addition, converting grain dryers to combust green ammonia rather than propane and natural gas may only require minimum modifications and expense.  The bottom-line is that with green ammonia there is a drop-in, zero-carbon nitrogen fertilizer that farmers can immediately incorporate with no changes and a drop-in, zero-carbon fuel that farmers can use in grain dryers with limited modification.  With minimum disruption, a 78% reduction of the energy footprint of corn production can be achieved.  An added benefit of this approach is that green ammonia fuel can eventually be a centerpiece for a sustainable agriculture and energy framework.  Renewable power generation from wind and solar can be used to meet the electric load when required and then be used produce green ammonia if generation exceeds electric demand.  The ammonia can then be used for fertilizer and fuel for engine generators, fuel cells, grain dryers, boilers, tractors, and trucks.    

Matt Palys, a PhD graduate student under Professor Prodromos Daoutidis in the Department of Chemical Engineering and Material Science, has modeled various scenarios using green ammonia as both fertilizer, energy storage for electric generation, and fuel for vehicles and heating.  Two significant findings are:

  • Green ammonia has a very desirable emissions avoidance cost projection at $18 / ton of CO2 (Palys et al. (2019). Chem. Eng. Process., 140, 11-21), and
  • A combination of green hydrogen and ammonia is significantly more cost effective in storing electricity than battery technologies (Palys & Daoutidis. (2020). Comput. Chem. Eng., 136, 106875).

So a final question may be ‘what is the cost of green ammonia?’  The current wind-to-ammonia pilot plant can produce green ammonia at approximately three times the local retail price –clearly too expensive for farmers to use.  However, when modeling the cost of production incorporating new production technologies developed by our ammonia research team and partners, we are projecting green ammonia prices below $450 / ton which is cost completive with brown ammonia.  In the near future, we hope to demonstrate these new green ammonia production technologies at the West Central Research and Outreach Center!