Element Optimum concentration Unit Reference N 1.48-3.0 % [24,25] P 0.1-0.5 % [22] K 0.75 % [24,25] S 0.20 % [24,25] Cl 0.273 % [22] Ca 1.60 % [24,25] Mg 0.3 % [24,25] Na 0.3-0.42 % [22] Al 160 mg kg-1 [24,25] Cu 12 mg kg-1 [24,25] Zn 18 mg kg-1 [24,25] Mn 600* mg kg-1 [24,25] Fe 110 mg kg-1 [24,25] B 17 mg kg-1 [24,25]

Note: Concentration of Mn is for tropical species with a range from 28 to 2257 mg kg-1, with most species containing 30 to 500 mg kg-1.

Table 3: Optimum nutrient concentrations in plants.