Mineral

Proposed critical levels

Reference

Nitrogen (N)

2 g/Kg soil

[113]

Phosphorus (P)

10 - 15 mg/Kg of soil

[114]

Exchangeable cations

Potassium (K)

0.20 cmol/ Kg of soil

[115]

Magnesium (Mg)

2 cmol/Kg of soil

[116]

Calcium (Ca)

5.0 cmol/ Kg of soil

[117]

Aluminum (Al)

1.0 cmol/ Kg of soil

[116]

Cation exchange capacity (CEC)

6.0 - 12.0 cmol/Kg of soil (for poor soils)

[113]