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Calculating the 2025 Dutch Fertilization Norms

This guide explains how the FDM Calculator determines the official Dutch legal usage norms (gebruiksnormen) for nitrogen and phosphate for the year 2025. These calculations are essential for ensuring your farm management plan complies with national environmental regulations.

The FDM Calculator automates these complex calculations based on your specific farm, field, and cultivation data. It calculates three key norms:

  1. Nitrogen Usage Norm (Stikstofgebruiksnorm): The maximum effective nitrogen from all fertilizers.
  2. Phosphate Usage Norm (Fosfaatgebruiksnorm): The maximum phosphate, based on your soil's phosphate status.
  3. Animal Manure Usage Norm (Dierlijke Mest Gebruiksnorm): The maximum nitrogen from animal manure, with specific rules for derogation farms.
Official Source & Disclaimer

The calculations in this document are based on the official 2025 norms published by the RVO (Rijksdienst voor Ondernemend Nederland). While we strive for accuracy, this document is for informational purposes only.

Always consult your agricultural advisor for definitive guidance and values tailored to your specific situation. FDM is not liable for any discrepancies or decisions made based on this information.

1. How the Calculator Works: Required Data​

To calculate the norms for a specific field, the FDM Calculator requires the following information for the 2025 calendar year.

  • Farm Details:

    • Derogation Status: Does the farm have a derogation permit for 2025? This is a critical factor for nitrogen and animal manure norms.

  • Field & Location:

    • Field Location: The precise geographical coordinates of the field are used to determine if it falls within special regulatory zones, such as Nutrient-Polluted Areas (NV-gebieden), Groundwater Protection Areas (GWBG-gebieden), or specific soil regions (sand, clay, peat, loess).

  • Cultivation Plan for 2025:

    • Main Crop (hoofdteelt): The primary crop grown on the field. The calculator identifies the main crop as the one with the longest cultivation period between May 15th and July 15th.
    • Crop Variety: For certain crops like potatoes and flowers, the specific variety can result in a higher or lower nitrogen norm.
    • Cultivation Dates: The start and end dates of cultivation are crucial for time-sensitive norms, such as those for temporary grassland.

  • Latest Soil Analysis Data:

    • Phosphate Levels: The P-CaCl2 (or P-PAE) and P-Al values from your most recent soil test are used to classify the soil's phosphate status, which directly determines the phosphate usage norm.

2. Nitrogen Usage Norm (Stikstofgebruiksnorm)​

This norm sets the maximum total nitrogen (in kg N/ha) that can be applied. The calculation follows a step-by-step process to find the most precise norm.

Calculation Steps​

  1. Identify Main Crop: The calculator determines the main crop for 2025 based on your cultivation plan.

  2. Determine Geographical Context: Using the field's location, the system checks:

    • If the field is in a Nutrient-Polluted Area (NV-gebied), which results in a stricter (lower) norm.
    • The dominant soil region (zand_nwc, zand_zuid, klei, veen, or loess).

  3. Find the Standard Norm: The calculator looks up the main crop in the official RVO Table 2 (implemented as nitrogenStandardsData).

  4. Apply Specific Rules: For various crops, the standard norm is refined with additional rules:

    • Temporary Grassland (Tijdelijk grasland): The norm is adjusted based on the cultivation end date.
    • Potatoes (Aardappelen): The norm is adjusted based on the potato variety, which may be classified as requiring a high, low, or standard nitrogen level. See RVO Tabel 2c. If the variety is unknown or not on the list of RVO Tabel 2c, the standard norm is used as "overig".
    • Maize (Mais): The norm depends on the farm's derogation status (is_derogatie_bedrijf).
    • Outdoor Flowers (Buitenbloemen): A higher norm is applied if the flower variety is on a specific list (see note 8 at RVO Table 2); otherwise, the standard norm is used.

  5. Select the Final Norm: The final value is selected from the refined list based on the field's soil region and whether it is in an NV-gebied.

  6. Apply Nitrogen Usage Norm Reduction (Korting Stikstofgebruiksnorm): The total nitrogen usage norm can be reduced (korting) if specific conditions regarding catch crops (vanggewassen) or winter crops (winterteelten) are not met in the previous calendar year. This reduction only applies to fields on sand and loess soils.

    Reduction Rules​

    1. Winter Crop Exception: No reduction is applied if the main crop of the current year (2025) is a designated winter crop (winterteelt) and the field is located in a sand or loess region. This is because winter crops provide similar environmental benefits to catch crops.

    2. Catch Crop Rules (if no Winter Crop Exception): If the winter crop exception does not apply, the reduction depends on whether a catch crop was sown in the previous year (2024) and its sowing date:

      • No Reduction: If a valid catch crop (vanggewas) was sown by October 1st of the previous year, no reduction is applied.
      • 5 kg N/ha Reduction: If a valid catch crop was sown between October 2nd and October 14th of the previous year, a reduction of 5 kg N/ha is applied.
      • 10 kg N/ha Reduction: If a valid catch crop was sown between October 15th and October 31st of the previous year, a reduction of 10 kg N/ha is applied.
      • 20 kg N/ha Reduction: A reduction of 20 kg N/ha is applied if:
        • No valid catch crop was sown in the previous year.
        • A valid catch crop was sown on or after November 1st of the previous year.
        • A catch crop was sown but destroyed before February 1st of the current year.

    The kortingDescription in the result will provide details on why a specific reduction was applied (or not applied).

3. Phosphate Usage Norm (Fosfaatgebruiksnorm)​

This norm sets the maximum phosphate (in kg P₂O₅/ha) that can be applied, based on the soil's phosphate status and the land use type.

Calculation Steps​

  1. Determine Land Type: The calculator checks if the main crop is grassland (grasland) or arable land (bouwland).
  2. Determine Phosphate Class: Using the soil analysis data (P-CaCl2 and P-Al values), the soil is assigned a phosphate class: Arm (Poor), Laag (Low), Neutraal (Neutral), Ruim (Sufficient), or Hoog (High). The thresholds for these classes differ between grassland and arable land.
  3. Look Up the Final Norm: The land type and phosphate class are used to find the final norm in the table below.
KlasseGrasland (kg P₂O₅/ha)Bouwland (kg P₂O₅/ha)
Arm120120
Laag10580
Neutraal9570
Ruim9060
Hoog7540

The result includes the norm value and its source, for example, "Grasland: Neutraal".

4. Animal Manure Usage Norm (Dierlijke Mest Gebruiksnorm)​

This norm defines the maximum nitrogen from animal manure (in kg N/ha) that can be applied. The calculation is based on the farm's derogation status and the field's location.

Calculation Rules​

  1. No Derogation: If the farm does not have a derogation permit, the norm is 170 kg N/ha.

  2. With Derogation: If the farm has a derogation permit, the norm depends on the field's location:

    • The system checks if the field is in a Nutrient-Polluted Area (NV-gebied) or a Groundwater Protection Area (GWBG-gebied).
    • If it is in either of these sensitive areas, the norm is 190 kg N/ha.
    • If it is outside these areas, the norm is 200 kg N/ha.