GB/T 29401-2020 in English

Core parameters of sustained-release performance:

• One-day nitrogen dissolution rate: 24h dissolution amount in still water at 38℃, reflecting the proportion of fast-acting nutrients
• Seven-day nitrogen dissolution rate: 7d cumulative dissolution amount in still water at 38℃, determining the release period (see Appendix B)

Type IV products require a seven-day nitrogen dissolution rate ≤20%, corresponding to a field release period of 9-10 months, suitable for economic crops with a long growing period.

New refractometer rapid determination method (Appendix A):

1. Reversely estimate the total amount of urea through the solid content
2. Establish a urea concentration-refractive index standard curve
3. The detection accuracy reaches 0.00001, which is 60% more efficient than the traditional titration method

Precautions for manufacturers:

• The amount and source of slow-release nitrogen nutrients must be indicated on the packaging
• HPLC method (ISO18643) is preferred for biuret content detection
• The addition of trace elements must comply with the requirements of GB/T34764