Strategies to Reduce on Farm Nitrous Oxide Emissions and Improve Nitrogen Use Efficiency

Nitrous oxide (N2O) emissions have exceeded projections by the Intergovernmental Panel on Climate Change (IPCC), endangering the goals of the Paris Agreement. Recent research has determined that N2O emissions are increasing at a faster rate than any other type of greenhouse gas emission, mainly due to a rise in nitrogen fertilizer application for food production (Tian et al., 2020). Nitrous oxide (N2O) is an important greenhouse gas that contributes to climate change. It has a long atmospheric lifetime (over 100 years) and is about 300 times better at trapping heat than is carbon dioxide (IPCC, 2013), even small emissions of N2O affect the climate. N2O depletes the stratospheric ozone layer, which protects the Earth from most of the sun’s ultraviolet radiation.  Nitrous oxide is produced by microbes in almost all soils.

Agricultural N2O Emissions

 In agriculture, N2O is emitted mainly from fertilized soils and animal wastes, wherever nitrogen (N) is readily available. In the United States, agriculture accounts for approximately 8 percent of all greenhouse gas emissions but contributes When not taken up by plants, most fertilizer N is mobile, hard to contain in the field and susceptible to loss. Nitrogen from fertilizer can be lost as nitrate to groundwater or as the gases N2O, dinitrogen (N2) or ammonia. Typically, only about half of the fertilizer N applied to a crop is taken up by the crop during that growing season (Cassman et al., 2002). Nitrogen applied more than crop needs is particularly susceptible to loss. Commercial, synthetic chemically concentrated fertilizers such as urea and ammonium phosphates have been widely adopted over the past 50 years to increase yields and help feed the world. Unfortunately, with current use practices, these fertilizers have been shown to degrade the soil over time, increasing salinity and acidity, lowering important microbial populations, potentially impacting the environment through runoff and leaching, contributing large volumes of GHG emissions. A 4R nutrient management approach to using these fertilizers would ensure efficient use of nitrogen and mitigate some of the related environmental issues. Fertoz N and P fertilizers are of high quality, provide yield benefits, and help correct some of these global climate issues.

4R Strategy

Fertilizer products/practices that delay the formation of nitrate are consistent in their ability to reduce N2O emissions. Urease and nitrification inhibitors are particularly consistent in this regard. Products and placements that influence the solubilization of the fertilizer product are influenced by the pattern of precipitation and as a result produce more variable results. Similarly timing of fertilizer N application interacts with the pattern of precipitation in determining the magnitude of reduction in N2O emissions. Determining the right rate of N fertilizer remains one of the greatest challenges establishing a 4R program. The need to consider all N sources and non-linear nature of N2O emissions to soil N availability complicate the determination of the right rate. The emergence tools to provide site specific measures soil N supply and plant N response would greatly assist the determinate of right rate. There is a greater realization and understanding emerging as to the role of other soil management and cropping practices in determining the potential for N2O emissions. The choice of the most appropriate 4R practices should consider the impact of these factors in determining the magnitude and timing of the potential for N2O losses

Farmers willing to participate in the program will be required to submit data to our carbon credit aggregator, to demonstrate their farming activities and their compliance to the 4R plan. Fertoz works with experts in satellite imagery and can also ensure fields are tested to ensure calibrated nitrogen application.

Table of Some 4R Practices

SourceRateTimePlace
Ammonium-based formulation and/or any of the following enhanced efficiency sources:                          ●Slow/controlled release fertilizers       
●Inhibitors; or                ●Stabilized N
Apply nitrogen according to qualitative estimates of field variability (landscape position, soil variability) using annual soil testing and recommendations developed with the 4R Plan                          OR                                  Apply nitrogen according to quantified field variability (e.g., digitized soil maps, grid sampling, satellite imagery, real time crop sensors) using annual soil testing and recommendations developed withing the 4R PlanApply in spring; or        Split apply; or               Apply after soil cools to 10°CApply in bands/ Injections

The 4R practice that most clearly result in reduced N2O emissions are:

Source-The use of enhanced efficiency N fertilizer sources, in particular nitrification and urease inhibitors, has been shown to be a reliable means of reducing N2O emissions. Cover crops such as legumes also mitigate some conventional N fertilizer requirement and reduce manufacturing demands upstream, resulting in overall emissions reductions. Generally, legumes fix up to 80% of the N needed to grow and will scavenge for the other 20% from the soil (Abdalla et al., 2019). Crops grown after legumes can take up at least 30-60% of the N produced by the legume (Abdalla et al., 2019). The N released from legumes is rapid compared to other cover crops and is more readily available when the cover crop is incorporated or mowed down. This also helps reduce N losses from material on the soil surface. As much as 140 lb. N/A has been measured 7 to 10 days after plow-down of hairy vetch (Sullivan et al., 2020). Non-Legumes can help reduce N fertilizer input requirements by taking up and storing excess soil N which might otherwise be lost to leaching or volatilization.

Alternative fertilizer sources such as alfalfa-based fertilizer products can significantly reduce both CO2 and N2O emissions. Fertoz offers alfalfa-based products such as Alfalfa Green (3-0-2) and Nutrient Vigour (4-4-0) and Nutrient Vigour Plus (2-4-4-2) which provide the soil with high quality organic fertilizer. N in the alfalfa pellets is more stable than urea N, as such it is far less volatile and less likely to leach.  Alfalfa Green provides nitrogen and is loaded with organic matter (42 %). This sedimentary based fertilizer pellet steadily releases nitrogen during the growing season, and is a soil conditioner, a soil amendment, and anti‐compaction agent. Nutrient Vigour Plus adds over 30 nutrients to balance the soil, including calcium, and contains fiber to improve soil moisture retention. This can be used to neutralize acidic soil and buffer alkaline soil. Alfalfa fertilizer products can be used as effective organic soil amendments to improve soil quality and plant health by adding organic matter and nutrients in a variety of crops. Alfalfa pellets are easy to handle, transport and apply making them an appealing, low-cost source of nitrogen. Studies have shown the application of alfalfa pellets can increase soil organic carbon and nitrogen(Malhi 2012; Stefankiw, 2012), which stimulate soil microbial activity and build soil health. Additionally, alfalfa fertilizer has been seen to stimulate plant growth increasing plant biomass,yield, and uptake of P, K, and S in crops such as maize, wheat, barley, canola and numerous vegetable crops (Qian et al., 2008; Qian et al., 2011; Stefankiw, 2012; Miyasaka et al., 2001; Ertani et al., 2013; Dion et al., 2020; Ries et al., 1977. Alfalfa pellets can improve soil conditions and help resist drought stress owing to their high capacity to absorb and retain water, increasing the overall water holding capacity of the soil(Qian et al., 2008; Miyasaka et al., 2001).

Place-Fertilizer placement can increase the efficiency of fertilizer N use by reducing NH3emissions, but in some cases, this may result in increased N2O emissions. It has also been shown that placement interacts with tillage system to influence N2O emissions.

Timing–Reduction in N2O emissions associated with fall application of N fertilizer, practiced in prairie Canada, can be achieved by delaying the application until soil temperature declines below 50 Celcius and/or by using urease/nitrification inhibitors. Split application of N fertilizers during the growing season is effective in reducing N2O emissions when there is the potential for N2O loss during the early growing season.

Rate–The greatest opportunities for reducing N2O emissions are associated with lower rates of N fertilizer application. Better accounting for soil and residue N sources and targeting N rates for maximal N use efficiency have been shown to result in reduced N2O emissions.

There are also opportunities for a reduction of N2O emissions associated with non-4R practices. The consideration of crop rotation effects on carbon and nitrogen availability, impact of tillage system, the use of tile drainage and the inclusion of legumes in rotation are all important in assessing the potential for N2O emissions and developing 4R practices to reduce N2O emissions.

To fully realize potential reductions in N2O emissions, increased nitrogen use efficiency resulting from the implementation of 4R practices should result in a corresponding reduction in the optimal rate of N fertilizer and thereby a reduction in N2O emissions (Zebarth et al. 2012; Rose et al. 2018).

As prices of urea fertilizer continue to rise or soil N is limited, it may be beneficial to offset N requirements by growing cover crops between cash crops. Legume cover crops can provide a source of readily available N shortly after they’ve been incorporated into the soil (<2 weeks) (Clark, A. 2007). Cover crops provide multiple benefits that can help boost farm profits during the first of planting and improve your bottom line even more in subsequent growing years. Different cover crops perform different functions in field making them a flexible and widely adaptable strategy for soil carbon and nitrogen management. Benefits of cover crops include cutting fertilizer costs, reduce the need for herbicides and other pesticides, improve yields by enhancing soil health, prevent soil erosion, conserve soil moisture, protect water quality (Clark, A. 2007), organic matter buildup, better soil structure, improve water holding capacity and infiltration, more efficient long-term nutrient, storage, scavenge nutrients from soil profile depths to make available to cash crop.

N-availability from Legumes

Generally, legumes fix up to 80% of the N needed to grow and will scavenge for the other 20% from the soil (Clark, A. 2007). Crops grown after legumes can take up at least 30-60% of the N produced by the legume (Clark, A. 2007). The N released from legumes is rapid compared to other cover crops and is more readily available when the cover crop is incorporated or mowed down. This also helps reduce N losses from material on the soil surface. As much as 140 lb. N/A has been measured 7 to 10 days after plow-down of hairy vetch.

N-availability and Carbon Sequestration from Non-Legumes

Non-Legumes can help reduce N fertilizer input requirements by taking up and storing excess soil N which might otherwise be lost to leaching or volatilization. Grasses like rye provide high amounts of carbon relative to nitrogen (C:N) making them a good builders of soil organic matter. The amount of carbon to be returned to the soil is in part dependant on the duration the cover crop is allowed to grow. More plant biomass provides more organic matter but will take longer to decompose the wider the C:N gets (>30:1).

References

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