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Critical levels of soil organic carbon (OC), and manganese (Mn)
| Organic carbon (%) | Rating |
|---|---|
| >20 | Very high |
| 10.0–20.0 | High |
| 4.0–10.0 | Medium |
| 2.0–4.0 | Low |
| <2 | Very low |
| Manganese (ppm) | |
| <20 | Deficient |
| 20–500 | Sufficient |
| >500 | Excessive/toxic |
Source: Landon [71]
