RB209 Nitrogen Calculator — UK 2026
Getting nitrogen rates right is one of the highest-value decisions in arable and grassland management. Too little and yield suffers; too much and you're wasting money, risking leaching, and potentially breaching NVZ rules. This calculator uses AHDB RB209 2023 recommendations as the starting point, then adjusts for your specific situation.
What is the SNS index?
Soil Nitrogen Supply (SNS) index (0–6) represents the estimated amount of mineral nitrogen your soil will supply to the crop during the growing season, from mineralisation of organic matter, previous crop residues and other sources. A soil N supply test (0–90cm cores, March sampling) gives the most accurate value, but field history is a reliable guide for most farms.
Frequently Asked Questions
- How much nitrogen does winter wheat need per hectare?
- RB209 recommends 140–220 kg N/ha for feed winter wheat at 8 t/ha target yield, depending on SNS index. Milling wheat needs an extra ~20 kg N/ha for protein. Add 20 kg N/ha for each tonne above 8 t/ha target.
- How much nitrogen does OSR need per hectare?
- Winter OSR needs 170–250 kg N/ha at SNS index 0–3 for a 3.5 t/ha target. The N response rate is 50 kg N/ha per t/ha — the highest of any combinable crop.
- What is the maximum N allowed under NVZ rules?
- In NVZ areas, total N from organic sources (manures, slurry, digestate) must not exceed 170 kg N/ha/year. Total fertiliser N has no single cap but applications must follow a compliant nutrient management plan.
- Does grass need more nitrogen than wheat?
- Intensively managed cutting grass can require 250–280 kg N/ha/year (split across cuts), more than most combinable crops. However it is spread across a long growing season with multiple applications.