Kinds of Fertilizers

The most important potassium fertilizers are shown in Table 4.9 (15). Two major groups may be distinguished, the chlorides and the sulfates. The latter are more expensive than the chlorides. For this reason, the chlorides are preferred, provided that the crop is not chlorophobic. Most field crops are not sensitive to chloride and should therefore be fertilized with potassium chloride (muriate of potash). Oil palm (Elaeis guineensis Jacq.) and coconut (Cocos nucifera L.) have a specific chloride requirement, with Cl functioning as a kind of plant nutrient because of its osmotic effect (110).


Potassium nitrate is used almost exclusively as foliar spray. Potassium metaphosphate and potassium silicate have a low solubility and are used preferentially in artificial substrates with a low K⁺-binding potential to avoid too high K⁺ concentrations in the vicinity of the roots. Potassium silicates produced from ash and dolomite have a low solubility, but solubility is still high enough in flooded soils to feed a rice crop (111). The silicate has an additional positive effect on rice culm stability. Sulfate-containing potassium fertilizers should be applied in cases where the sulfur supply is insufficient; magnesium-containing potassium fertilizers are used on soils low in available magnesium. Such soils are mainly sandy soils with a low cation exchange capacity.