Dynamics and transformations of micronutrients in agricultural soils as influenced by organic matter build-up: A review

The dynamics and transformations of micronutrients (Zn, Cu, Fe, Mn, B and Mo) in soils, are governed by various factors like pH, EC, soil organic matter etc. Soil organic matter (SOM) is known to modify different physiochemical reactions that influence the available component of micronutrients. Soil organic matter favors reduced (lower redox potential) environment and enhances the accessibility of micronutrient cations in the soil. Also, SOM has direct and indirect impacts on nutrient transformations. Soil organic matter (SOM) also serves as source of soil organic carbon (SOC) comprising about 60% on a mass basis. Under reduced environment the addition of SOM increased complexed forms of micronutrients. Build-up of SOM in soil converts adsorbed fractions to more plant-accessible forms of micronutrients. Soil organic matter addition increases the water soluble and exchangeable forms of micronutrients in soil which further increase the uptake of micronutrients. High amount of SOM in soils assists the various reactions of micronutrients resulting in formation of more stable complexes of micronutrient. Soil organic matter binds more Zn, Cu, B and Mo compared to Fe and Mn because the former are less sensitive to redox changes. The accretion of organic matter near the soil surface increases transformations (towards adsorbed fractions) of Mn and Fe and possibly decreases the availability of Zn, Cu, B and Mo by causing their redistribution among other complex fractions.