N-min measurement: How much nitrogen is actually available to your crop?

30 October 2026

A fertilization plan provides guidance, but it doesn’t tell the whole story about the current situation in the field. After a wet winter, a dry spring, or a period of high mineralization, the amount of mineral nitrogen in the soil can differ significantly from what was previously expected. An N-min measurement provides insight into this nitrogen supply.

An N-min measurement determines the amount of mineral nitrogen present in a sampled soil layer. The analysis quantifies the amounts of nitrate and ammonium nitrogen. These data provide insight into the available nitrogen supply and help assess nitrogen availability for the crop.

Measuring for More Targeted Fertilization

In practice, farmers often rely on standards, fertilization recommendations, and experience from previous years. However, weather conditions and soil processes can cause actual nitrogen levels to differ from expectations.

“You might think there’s still enough nitrogen available, but without a measurement, that remains an assumption,” says Robalab. “An N-min measurement provides you with up-to-date data, which can be used as a tool when formulating a fertilization recommendation.”

The measurement results can help determine whether to apply additional nitrogen, but also support the decision not to apply extra fertilizer. This allows fertilization to be better tailored to the specific conditions of the field.

Especially valuable in the spring

N-min measurements are taken at various stages of the growing season. In the spring, the analysis provides insight into the available mineral nitrogen supply, and this information can be used to determine the fertilization strategy.

A post-harvest measurement is also valuable. The amount of mineral nitrogen remaining in the soil at that time provides insight into the nitrogen residue after the crop has been harvested. This is relevant not only for nitrogen utilization but also for assessing the risk of nitrogen losses.

Mineral Nitrogen and the Risk of Nitrate Leaching

Mineral nitrogen that remains in the soil after harvest can be further leached into deeper soil layers by precipitation. When nitrate is carried into the groundwater along with excess precipitation, this can contribute to a deterioration in groundwater quality.

The amount of mineral nitrogen in the soil is therefore an important indicator when assessing the risk of nitrate leaching.

The measurement does not directly determine how much nitrate ultimately ends up in the groundwater. Factors such as soil type, precipitation, crop uptake, nitrogen mineralization, and the presence of a cover crop also play a role in this process.

A Role in the Development of Target-Based Management for Water Quality

The importance of understanding mineral nitrogen reserves aligns with the development of farm-specific water quality target-based management. The draft of the 8th Nitrates Directive Action Program focuses on an approach in which water quality and the performance of individual farms play a greater role.

Measurements of mineral nitrogen residue can contribute to understanding the risk of nitrate leaching within this framework. Thus, N-min measurements are relevant not only for fertilization strategy but also for the broader challenge of limiting nitrogen losses to groundwater and surface water.

Not all soils react the same way

The amount of available nitrogen is influenced by various factors, such as soil type, organic matter, temperature, precipitation, and crops grown in previous years. As a result, fields that are close to one another can still differ significantly from one another.

That is precisely why it is valuable not to rely solely on general recommendations, but also to use up-to-date measurement data from your own field. This provides a more well-founded picture of the nitrogen supply and the opportunities for improving nitrogen utilization.

Reliable results start with a thorough analysis

An N-min measurement is only valuable if sampling and analysis are performed carefully. The representativeness of the soil sample and the correct sampling depth are key considerations in this regard.

Robalab possesses the expertise and analytical methods needed to assess the mineral nitrogen content in the soil. We apply this expertise to our projects. We currently serve as the testing laboratory for N-min Uitvoering B.V., which is preparing for the target-based management requirements under the 8th Nitrate Program. The results provide growers with a well-founded basis for fertilization decisions and help them gain a better understanding of nutrient availability and nitrogen residues in their soil.

Would you like to know how much mineral nitrogen is present in your soil?

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