Compare compost and digestate on the same laboratory basis

Steps
1. Record the sample date, material identity and laboratory method. Ask whether a result is per tonne of fresh material or per tonne of dry matter. Do not mix total nitrogen with ammonium nitrogen or a modelled plant-available fraction.
2. Convert only when the necessary measurement exists. In the example, material A contains 25% dry matter and 12 kg total N per tonne of dry matter: 0.25 × 12 = 3 kg total N per tonne fresh. Material B is already reported on a fresh basis.
3. Compare the same field question: what information is still needed for this crop, soil, season and regulatory setting? Total nutrient mass alone does not establish crop availability, soil suitability or legal permission.
4. Hold the decision when contamination, salinity, stability, storage history or applicable requirements remain unknown. Request the relevant analysis and qualified local interpretation rather than treating a blank cell as zero.

Worked record
Material A · fictional compost: ____________________
Material B · fictional digestate: ____________________
Equal 10 t fresh comparison: ____________________
Still missing for both: ____________________
Decision record: ____________________

Material A · fictional compost: Dry matter 25%; total N 12 kg/t dry matter → 3 kg/t fresh
Material B · fictional digestate: Dry matter 8%; total N 5 kg/t fresh → already comparable for total N
Equal 10 t fresh comparison: A: 30 kg total N; B: 50 kg total N. This is mass arithmetic, not an application recommendation.
Still missing for both: Ammonium N, availability assumptions, crop need, soil analysis, contaminants and local limits
Decision record: No field rate selected; responsible adviser requests the missing tests.

Do not infer that B is “better” from the higher total nitrogen alone. The materials can serve different purposes, and losses depend on handling and conditions. Keep the original laboratory report with the converted worksheet so another reader can reconstruct both the calculation and its limits.

Wageningen University & Research: compost handbook — https://edepot.wur.nl/375218