It is found in minerals fixed in the form of sulfur. Compared to Cu it is more mobile because its sulfur is more soluble.

The average content of Zn in soil is between 10 and 300 ppm.

The adsorption of Zn occurs in the places of change of the clay minerals and in the organic complex of the plant. It has been studied that approximately 60% of the soluble Zn occurs in the form of organic complexes associated with amino acids and humic acids.

The solubility of Zn in the soil and its minerals is maximum at pH4; going down significantly in neutral conditions and being minimal in alkaline.
P induces Zn deficiency in many soils, due to the formation of zinc phosphates, responsible for the deficiency.

In the plant:

• The mobility of Zn in the plant is low; it tends to accumulate in the roots but the mobility towards the young tissues is deficient.
• Important interactions between Zn and Fe occur, as well as Zn and P that can affect the transport of Zn. In plants with deficiencies of Zn have been detected high levels of Fe and P; and, Fe is a clear competitor of Zn for the combination with chelating agents.
• Also, Cu can significantly affect the absorption of Zn by competing both elements for the same places of absorption of the plant.

Physiology of Mo:

• It has an enzymatic function like that of Mn and Mg.
• It is also an essential constituent of various dehydrogenases such as lactic acid and glutamic acid.
• Zn participates in the making of RNA, demonstrating low levels of this nucleotide in deficient conditions. It also participates in protein formation, amino acid synthesis and nitrate reduction.
• The function of Zn in the metabolism of auxins, deserves special mention, since it is related to the regulation of the synthesis of tryptophan, precursor of indoleacetic acid. It has been demonstrated that low levels of Zn coincide with low levels of AIA, even with subsequent applications of Zn the levels of this have been corrected.

Zn in the nutrition and fertilization of crops:

• Zn is a very widespread deficiency and is among those with the highest incidence on yields.
• Among the main factors capable of generating deficiencies are not usually poor levels of Zn in soil, but conditions that are not prone to its assimilation; among which stand out a pH higher than 7 and high contents of calcium carbonate, or limestone lands.
• Also noteworthy is the correlation between low temperatures in soils and low absorption of Zn in plants such as tomatoes.
• High levels of solar radiation contribute instead to the elimination of symptoms of deficiencies.
• It has been demonstrated that the presence of chelates in the soil as a result of the decomposition of organic matter and root exudation contributes to maintain good levels of Zn in the plant. The
• Ca acts here as a competitor of the Zn; moving it.

Conclusion about conditions of deficiencies in Zn:

• Low levels in soil.
• Limestone soils, diatoms …
• Low concentrations in humic acids.
• Cold areas.

In conditions of poor root formation attributed to compact, poorly aired soils … the application of Zn is recommended, or the application of techniques that contribute to the correction of them.

Detection of deficiencies: logically foliar symptoms or the leaf analysis if the deficiency is not severe, but it exists. Note that the foliar contents of Zn below 20-25 ppm are low, being deficient clearly below 10 in apple, citrus, corn, tomato, alfalfa and soybean.

Zn deficiencies:

The main crops in which Zn deficiencies have been detected are citrus, corn and fruit trees.

In general, all agree on internervial chlorosis, reduction of the size of the leaves and malformations.