Definition

The N-Index instantly indicates whether the nitrogen supply for a specific grass cut was sufficient. It shows whether the nitrogen input was appropriate relative to the silage quality. This makes the N-Index a valuable tool for producing high-quality grass silage and improving nitrogen use efficiency.

Importance

Adequate nitrogen (N) is essential for optimal grass growth and forage quality. Nitrogen is a key component in protein synthesis. Assessing nitrogen adequacy requires extensive data, as it depends not only on fertilisation but also on soil type, nitrogen mineralisation, and the maturity stage of the crop.

Grass silage comparison: Nitrogen Supply & Soil K-Index

To compare different grass silages in terms of nitrogen supply, several variables are considered, including nitrogen content in the form of ammonia (included in total crude protein), the potassium level in the soil (K-index), and more.

NDF standardisation

Grass silages are standardised to an NDF content of 522 g/kg dry matter, representing the average Dutch grass silage. NDF (Neutral Detergent Fibre) is an indicator of cell wall content and crop maturity. Younger grass has lower NDF and more digestible nutrients; mature grass has higher fibre and lower protein due to dilution.

The N-index integrates all relevant variables into a single practical indicator, clearly showing whether the nitrogen supply was in balance with silage quality.

Interpreting the N-Index

A target-range N-index means the protein-to-sugar ratio in the silage is optimal, which supports good preservation.

A high N-index may indicate insufficient sunlight during harvest or excess respiration, leading to a suboptimal protein-sugar ratio and poor fermentation. This reduces organic matter retention and feed efficiency. Deviations from the target can be corrected by adjusting nitrogen applications or harvest timing.

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