Variable-rate nitrogen application to reduce emissions

Applying nitrogen (N) fertiliser where a field most needs it makes economic and agronomic sense; it also helps reduce greenhouse gas (GHG) emissions. By tailoring N to real-time crop and grass requirements, variable-rate application can boost N use efficiency and lower environmental impact.

Variable-rate N application adjusts fertiliser rates within individual fields by responding to spatial difference in crop demand. Here’s how the process works:

• Assess crop requirements  
  • Remote sensing: uses satellite or drone imagery to measure light reflectance from the crop canopy to calculate N needs. A map of the field is made with this data and given to the fertiliser spreader
  • Live, in-field sensing: crop sensors mounted on the fertiliser spreader provide real-time data
• Use a variable rate fertiliser spreader. This will take the mapping or live information and use it to guide N application to precisely where it is needed and at the required rate across different zones. This reduces over- and under- application

Applying N at the precise rate that every part of the field needs maximises yield potential.

• Greenhouse gas (GHG) emissions associated with fertiliser application can be limited
• Air pollution from ammonia will be reduced
• Nitrate leaching into watercourses will be prevented if the land isn’t carrying more N than it needs

• Some areas of a field may need less N, reducing overall use
• With continued fertiliser price volatility, using N inputs in an efficient way can protect farm profit margins

• Results in more uniform crops and grassland and will optimise yield and N use
• By using mapping to identify poorly performing areas, other corrective action can be taken – for example, it might draw attention to drainage issues

• It’s a valuable tool for farms within catchment sensitive areas and nitrate vulnerable zones (NVZs) that must comply with additional controls on their input use
• Precision application can reduce the amount of N used if some areas had been getting more than they needed

• Accurate data is essential for making the most of variable-rate technology. Start by assessing crop and field variability.
• Use satellite or drone imagery to map crops and identify differences in N demand
• Mapping options will vary depending on your chosen service provider
• Historical yield maps and soil tests can also help inform zone management

• Farms can invest in their own equipment or use contractors
• Equipment must be able to read a mapping file and adjust fertiliser rates accordingly
• Regular calibration is essential to ensure accuracy and consistent performance

• Before application, understand the N content of the fertilisers being applied
• Organic fertilisers should be tested for N content, as nutrient levels can vary widely
• This ensures the correct rate based on actual nutrient availability

Reducing reliance on slug pellets and advancing alternative biological control is an economically viable approach.

SLIMERS builds on previous work and combines expertise across the consortium to develop:

• Cost-effective digital autonomous slug monitoring and spot treatment
• Slug forecasting and precision application tools
• The knowledge and understanding to control slugs more sustainably