Fosfaatgebruiksnorm 2025

This document provides a detailed explanation of the Dutch legal usage norm (gebruiksnorm) for phosphate in 2025. It covers how the norm is calculated and how the amount of applied phosphate counts towards this norm (opvulling), with a special focus on the regulations for organic-rich fertilizers as introduced in the 7th Action Programme Nitraatrichtlijn.

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Calculating the Gebruiksnorm (Usage Norm)

How the Norm Works

The phosphate usage norm defines the maximum amount of phosphate (in kg P₂O₅ per hectare) that can be applied to a parcel of land. This maximum is determined by two key factors: the land use type and the phosphate status of the soil.

The process involves three steps:

1. Determine Land Type: First, the land is classified as either grasland (grassland) or bouwland (arable land) based on the main crop.
2. Determine Phosphate Class: Based on a recent soil analysis (using P-CaCl₂ and P-Al values), the soil is assigned a phosphate class. The classes range from Arm (Poor) to Hoog (High). The specific thresholds for each class differ for grassland and arable land.
3. Look Up the Final Norm: The combination of land type and phosphate class determines the final usage norm, as shown in the official table below.

Klasse	Grasland (kg P₂O₅/ha)	Bouwland (kg P₂O₅/ha)
Arm	120	120
Laag	105	80
Neutraal	95	70
Ruim	90	60
Hoog	75	40

The result of this calculation is the maximum allowable phosphate application for the parcel.

How the FDM Calculator Determines the Norm

The fdm-calculator uses the calculatePhosphateUsageNorm function, located in fdm-calculator/src/norms/nl/2025/value/fosfaatgebruiksnorm.ts.

This function requires the following inputs, defined in input.ts:

• Main Crop: To determine if the land is grasland or bouwland.
• Soil Analysis Data: The latest P-CaCl₂ and P-Al values.

The core logic uses fosfaatgebruiksnorm-data.ts, which contains the official thresholds for phosphate classes and the corresponding norm values for both grassland and arable land.

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Calculating the Opvulling (Filling)

How the Filling Works

The "filling" (opvulling) refers to how much of the applied phosphate counts towards the usage norm. While most fertilizers count for 100% of their phosphate content, the Dutch government encourages the use of organic-rich fertilizers (Organische Stofrijke meststoffen) to improve soil quality. To stimulate their use, these fertilizers count for a lower percentage of their phosphate content.

Differentiated Percentages for Organic-Rich Fertilizers

The phosphate in qualifying organic-rich fertilizers counts towards the usage norm according to the following differentiated percentages:

• 25% of phosphate counts for:

  • GFT-compost
  • Groencompost (Green compost)

• 75% of phosphate counts for:

  • Vaste strorijke mest van rundvee (Straw-rich solid manure from cattle)
  • Vaste strorijke mest van varkens (only for organic farms) (Straw-rich solid manure)
  • Vaste strorijke mest van schapen (Straw-rich solid manure from sheep)
  • Vaste strorijke mest van geiten (Straw-rich solid manure from goats)
  • Vaste strorijke mest van paarden (Straw-rich solid manure from horses)
  • Champost

• 100% of phosphate counts for:

  • All other fertilizers, including mineral fertilizers and other organic fertilizers not listed above.

Conditions for Differentiated Percentages

To use these lower percentages, two important conditions must be met:

1. Minimum Application: At least 20 kg P₂O₅ per hectare of a specific organic-rich fertilizer must be applied. This ensures the application is substantial enough to contribute to soil improvement.
2. Maximum for Differentiated Calculation: The differentiated percentage (25% or 75%) applies only to the amount of phosphate up to the parcel's maximum usage norm. If you apply more phosphate from an organic-rich source than the norm allows, the excess amount counts for 100%.

Calculation Examples

Example 1: Standard Application

• Parcel: Arable land, phosphate status Ruim.
• Norm: 60 kg P₂O₅/ha.
• Application: 10 tons/ha of straw-rich cattle manure (forfaitair: 3.2 kg P₂O₅/ton).

1. Total Phosphate Applied: 10 ton/ha × 3.2 kg P₂O₅/ton = 32 kg P₂O₅/ha.
2. Check Conditions:
   • The applied amount (32 kg) is > 20 kg (minimum met).
   • The applied amount (32 kg) is < 60 kg (norm).
   • The 75% rule applies.
3. Calculate Filling: 32 kg P₂O₅/ha × 75% = 24 kg P₂O₅/ha.
   • Result: Only 24 kg counts towards the 60 kg norm, leaving 36 kg of usage room.

Example 2: High Application of Compost

• Parcel: Grassland, phosphate status Arm.
• Norm: 120 kg P₂O₅/ha.
• Application: 210 kg P₂O₅/ha from green compost.

1. Check Conditions:
   • The applied amount (210 kg) is > 20 kg (minimum met).
   • The differentiated percentage of 25% applies up to the norm of 120 kg.
2. Calculate Filling:
   • Part 1 (up to the norm): 120 kg P₂O₅/ha × 25% = 30 kg P₂O₅/ha.
   • Part 2 (above the norm): The remaining phosphate is 210 kg - 120 kg = 90 kg. This amount counts for 100%.
   • Total Filling: 30 kg + 90 kg = 120 kg P₂O₅/ha.
   • Result: The total filling is 120 kg, which meets the 120 kg norm exactly.

How the FDM Calculator Determines the Filling

The fdm-calculator uses the calculatePhosphateFilling function, located in fdm-calculator/src/norms/nl/2025/filling/fosfaatgebruiksnorm.ts.

This function processes a list of fertilizer applications and implements the following logic:

1. It identifies which fertilizers are classified as organic-rich and determines their applicable percentage (25% or 75%).
2. For each application of an organic-rich fertilizer, it checks if the 20 kg P₂O₅/ha minimum is met.
3. It calculates the filling by applying the differentiated percentage to the phosphate amount that falls within the usage norm.
4. Any phosphate from an organic-rich fertilizer applied above the usage norm is counted at 100%.
5. All other fertilizers are always counted at 100%.

The function sums the calculated filling from all applications to provide the total phosphate filling for the parcel.