Soil Nutrient Cycling
Micronutrient Cycling
Four of the micronutrients (Cu, Fe, Mn, and Zn) are cation micronutrients, and are primarily positively charged ions in soil water. The other three micronutrients (B, Cl, Mo) exist either as neutral or negatively charged molecules in soil water and are referred to here as anion micronutrients.
Cation Micronutrients
The cation micronutrients exist in one of four forms in the soil: mineral, organic, sorbed (bound to soil), or dissolved. The majority of micronutrients in soil are bound in minerals and organic matter, and are unavailable to plants. Sorbed (e.g., adsorption or absorption) micronutrients represent the third largest pool, and are generally very tightly bound to soil surfaces. Although mineral, organic, and sorbed metals are not immediately plant available, they can slowly release metals into solution.
Anion Micronutrients
The anion micronutrients are boron, chloride, and molybdenum. Chloride and molybdenum generally exist as anions in soil, whereas boron generally exists as a non-charged acid (H3BO3), though it can exist as an anion at higher pH. The transformations that the anion micronutrients undergo are similar to the cation micronutrients with some major exceptions, largely due to charge differences. For example, chloride and boron have a much higher likelihood of leaching than the cation micronutrients because they are not positively charged, and do not sorb readily to clay particles.
Click on the following topics for more information on soil nutrient cycling.
