By the term ‘micronutrient availability’ we mean the total micronutrient
forms in soils, which are available for plants (i.e., all the soluble forms that can be taken
up by plants). Availability depends on solubility in soils, i.e., the solubility of
micronutrients in soils determines their availability for plants (thus their uptake) and
their downward mobility. Understanding the factors controlling trace element solubility
allows the selection of soil amendments that promote or reduce their availability and of
course the selection of the suitable plant species (those that are optimal for the desired
goal of managing trace element influx in the soil-plant system). There are many soil
factors influencing micronutrient solubility and availability for plants. The most
important of these factors are pH, organic matter content, CaCO3, soil texture, cation
exchange capacity (C.E.C.), erosion, soil moisture and temperature etc. Generally, trace
element solubility in soils depends on a plethora of physical (e.g., water retention
capacity), chemical (e.g., pH), microbial (e.g., mycorrhiza) and plant factors, as well as
on the properties of each nutrient, which are fully analyzed below. There are many
extractants (like DTPA, EDTA, Mehlich-1, Mehlich-3) used to determine available for
plants quantities of micronutrients in soils; since great differences exist in the
extractability of these chemical solutions, in order to estimate plant available
micronutrient concentrations it is absolutely necessary to study micronutrient
extractable concentrations in soils, in relation to their uptake by plants. All the topics
concerning micronutrient solubility in soils, together with the factors influencing
micronutrient availability and uptake by plants, are analyzed in detail in this chapter. In
addition, a comparison between the extractant solutions used to estimate plant available
quantities of micronutrients in soils is included in the second part of this chapter.
Keywords: CaCO3, cation exchange capacity (C.E.C.), micronutrient availability,
micronutrient solubility, organic matter, pH, soil moisture, soil texture, trace
elements.
