Factors Influencing the Availability of Micronutrients in Soil

After reading this article you will learn about the factors influencing the availability of micronutrients in soil.

(A) Factor Influencing the Availability of Micronutrients Cation:

Each of the 5 micronutrient cations i.e., iron, manganese, zinc, copper and cobalt is influenced in a characteristic way by the soil environment.

Following factors affect the availability of micronutrient cations:

1. Soil pH:

The micronutrient cations are most soluble and available under acid condition. In very acid soils there is a relative abundance of the ions of iron, manganese, zinc and copper. In fact, under these conditions the concentrations of one or more of these elements is often sufficiently high to be toxic to common plants.

As the pH is raised, their solubility to plants decreases because ionic form of cations are changed to the hydroxides or oxides. The desirability of maintaining an intermediate soil pH. Generally, zinc-fixation is found at high pH value.

2. Oxidation State and pH:

Three of the trace element cations are found in soils in more than one valent state. These are iron (Fe⁺⁺ Fe⁺⁺⁺), manganese and copper. The lower valent states are encouraged by conditions of low oxygen supply and relatively higher moisture level.

The oxidised state of iron, manganese and copper i.e., hydroxides or hydrous oxides are insoluble. The micronutrient cations and molybdenum and somewhat more are available under conditions of restricted drainage. Flooded soils generally show higher availability than well-aerated soils.

3. Inorganic Reaction:

The availability of iron and zinc may be reduced in the presence of excess phosphates. From a practical standpoint, phosphate fertilizers should be used in only those quantities that are required for good plant growth.

4. Organic Combinations:

Each of the micronutrient cations may be held in organic combination. These complexes may protect the micronutrients from certain harmful reactions, such as the precipitation of iron by phosphate. On soils high in organic matter, complex formation by copper is thought to be responsible for the deficiency of this element.

(B) Factors Influencing the Availability of the Micronutrient Anions:

Anions i.e., chlorine, molybdenum and boron are relatively little common in comparison to cations. Chlorine, molybdenum and boron are quite different chemically, so very similarity would be expected in their reaction in soils.

1. Chlorine:

The chloride ions are not tightly adsorbed by negatively charged clays and as a result are subject to movement. In semi-arid and arid regions, a somewhat higher concentration might be expected, the amount reaching the point of salt toxicity in some of the poorly drained saline soils.

2. Boron:

The availability and utilization of boron is determined to a considerable extent by pH. Boron is most soluble under acid conditions. It apparently occurs in acid soils in part as boric acid which is readily available to plants. Boron is held in organic combinations from which it may be released for crop use.

3. Molybdenum:

Soil conditions affect the availability of molybdenum much the same as they do that of phosphorus. For example, molybdenum in quite unavailable in strongly acid soils. The liming of acid soils will usually increase the availability of molybdenum.