Definition

The S-Index is an analytical indicator that provides an instant assessment of sulphur (S) availability in relation to the actual grass yield. It serves as a practical tool for farmers to evaluate whether sulphur supply has been sufficient during the growing season.

This insight supports informed decisions on sulphur fertilisation for the next season, aiming to produce high-quality forage protein and improve farm self-sufficiency and protein efficiency.

Importance of sulphur in grassland management

Sulphur plays a critical role in plant nutrition and forage quality:

• Amino acid synthesis: Sulphur is essential for the formation of amino acids, which directly influence protein quality in forage.
• Nutrient requirements: Productive grassland typically requires 35–45 kg of S per hectare (equivalent to 85–115 kg SO₃).
• Impact on yield: Field trials indicate that sulphur deficiency can reduce grass yields by 10–20%.
• Risk of excess: Over-application of sulphur can negatively affect the uptake of trace elements such as copper (Cu) and selenium (Se), potentially leading to animal health issues.

Interpreting the S-Index

Understanding the S-Index helps farmers align fertilisation strategies with grass growth and protein quality goals. Eurofins Agro’s S-Index assessment includes:

• Protein composition: Evaluates the balance of amino acids in forage.
• Cell wall content: Assesses structural components in relation to plant maturity.
• Sulphur levels: Measures sulphur availability and its influence on forage quality.

By integrating these factors, the S-Index provides actionable insights for optimising sulphur fertilisation and improving overall forage quality.

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