Reduce emissions by avoiding excess nitrogen use

How aligning nitrogen applications with crop need, farmers can boost productivity, meet environmental regulations, and support long-term sustainability.

When global pressures drove up the price of ammonium nitrate (AN), many farmers began looking more closely at how they use fertiliser – and for good reason.

Environmental regulations, including Nitrate Vulnerable Zone (NVZ) regulations, have also added pressure, requiring farmers to adhere to limits on organic and inorganic fertiliser applications and livestock numbers, to protect water quality and reduce emissions. 

Applying more nitrogen than crops can use not only wastes money but also increases nitrous oxide (N₂O) emissions, a potent greenhouse gas. By aligning nitrogen applications with crop need, farmers can boost productivity, meet environmental regulations, and support long-term sustainability.

Optimising nitrogen (N) use isn’t just about environmental responsibility – it also supports water quality, farm profitability, and long-term resilience.

• Excess nitrogen increases the risk of nitrous oxide (N₂O)
• Chemical fertilisers carry additional emissions from their manufacture, contributing to agriculture’s carbon footprint
• By cutting unnecessary N use, farmers contribute to UK agriculture’s emission reduction targets and climate goals

• Reducing excess N use helps lower nitrate leaching, protecting nearby water bodies from pollution
• Strategic nitrogen application remains important. In situations where yield is limited by N availability, small, well-timed applications can increase output without raising net GHG emissions
• Aim for realistic yield targets based on land capability and crop potential to optimise N use and minimise emissions per tonne of crop

• Applying more N than the crop needs is not cost-effective
• Farms that scaled back their N inputs when prices escalated found that yields weren’t impacted but only when reductions were backed by data-driven decisions
• Effective practices include:
  • Testing soil and manure to assess available nitrogen
  • Using tissue or sap tests to track crop needs through the season
  • Deploying in-field nitrogen sensors to fine-tune applications
  • Timing applications carefully in line with crop demand and weather conditions
• By narrowing the margin of error between applied and needed nitrogen, and adjusting timing to suit conditions, farmers can achieve better outcomes for both yield and emissions

Use the Soil Nitrogen Supply (SNS) approach outlined in our Nutrient Management Guide (RB209) to assess the supply of nitrogen and how much more is required. This includes N from:

• Fertilisers and manures
• Atmospheric deposition
• Mineralisation of soil organic matter and crop residues
• Leguminous crops
• Biological N fixation

This will help you work out the correct level of application needed, generally referred to as the ‘optimum’ level.

• Test organic fertilisers to find out how much N is being applied
• Tissue/sap testing can inform alternations to planned N use through the season
• Satellite imagery or N sensors can also be used

N use can be managed according to a plan, with crop and grass yields recorded at the end of the season to allow the plan to be revised the following year if needed.

Impacts will vary because rainfall and temperature both influence soil and microbial processes that drive rates of decomposition, denitrification and nitrification. The texture, drainage and pH of soil also comes into play.

By using best practice guidance, the N requirements applicable to the field, season and crop can be determined.

This helps you apply N more precisely across different parts of a field.

• Collect soil samples annually from a quarter of farm fields
• Get the nutrient levels in these tested at a recognised laboratory. The results can inform a nutrient management plan (NMP)
• Plans can be digital or paper-based, informed by RB209 or Scotland’s Farm Advisory Service Technical Notes

R-Leaf, developed by Crop Intellect Ltd, is a novel Agri-Tech solution aims at reducing agriculture’s carbon footprint. It involves spraying a photocatalyst onto crop foliage, where it uses sunlight to convert atmospheric nitrogen oxides (NO and NO₂) into usable nitrates. This technology becomes even more powerful when combined with nitrogen-fixing endophytic bacteria. These microbes form a symbiotic relationship with the plant, converting atmospheric nitrogen into ammonia for plant uptake in exchange for nutrients.

In the UK wheat trials using standard farm practices, combined R-Leaf with nitrogen-fixing bacteria led to a 5% higher yield than when either technology was used alone.