| Grade (mg∙kg−1) | Available Fe | Available Mn | Available Cu | Available Zn |
| Low | <4.5 | <5 | <0.2 | <0.5 |
| Middle | 4.5 - 10 | 5 - 15 | 0.2 - 1 | 0.5 - 1 |
| High | >10 | >15 | >1 | >1 |