Of all the elements, potassium is found in greatest quantity in plants, especially the young, in the form of inorganic salts.
Potassium deficiency is felt more strongly on soils with high salt content of calcium and magnesium and poor aeration. External symptom of potassium deficiency is the leaf color change, that the appearance of brown spots, especially near the extremities of the leaf. This phenomenon starts at the edge of the leaf, while the ribs and surrounding areas they remain green. Leaf edges curl and the ribs seem immersed in leaf tissues. In most plants these phenomena occur first at the older lower leaves.
Plants with potassium deficiency may have lower foliar surfaces and presents a reduction of the process of photosynthesis.
When excess potassium prolongs the period of vegetation and delayed maturation. Plants developed in terms of potassium enough fade faster and more pronounced than plants supplied with potassium.
Sodium plays a well defined role in vascular bands and fibers that support the plant tissue.
Halophile plants, adopted an environment with high concentrations of sodium, this element is necessary for growth, give a better color of the leaves, increases disease resistance.
It is found in soil. Magnesium absorption by plants is conditioned by three main factors: the amount of land accessible, magnesium interactions with other elements and requirements of the plant. Insufficient magnesium produces necrosis of leaves. Magnesium accumulate in seeds, formed with phosphoric acid, fitina.
Iron must be present in the soil in a form assimilable otherwise occurs deficiency manifested by green-sickness. Iron deficiency is associated with a yellowing of leaves.
Phosphorus is found in soil as organic and inorganic compounds. Soil organic phosphorus comes from the decomposition of organic residues from crop residues or organic fertilizers.