Geochemical Forms and Availabilities of Zinc, Copper, Iron and Manganese in Agricultural Calcareous Soils

Abstract

Deficiencies of micronutrients including zinc (Zn), copper (Cu), iron (Fe) and manganese (Mn) are important problems for crop cultivation in calcareous soils. Geochemical forms are the controlling factors of these cationic micronutrients availabilities. Thus, this study was to fractionate geochemical forms and investigate the relationship between the available and geochemical forms of four cationic micronutrients in six agricultural calcareous soils, which were distributed in Lop Buri and Nakhon Sawan provinces. The methodologies included, chemical analysis, extractions of available contents and geochemical forms of Zn, Cu, Fe and Mn by sequential extraction from the soil samples. The results showed that the available-Zn contents in six soils were not sufficient, but the contents of the available-Cu, Fe, and Mn were adequate. Zinc and Cu were mostly distributed in the residual fraction which were unavailable to plant. Whereas Iron and Mn were mostly distributed in organic-bound and Fe-Mn oxides fractions, respectively. In addition, the available forms of Zn, Cu and Fe were significantly correlated with the organic-bound fractions. Whereas, available-Mn was not correlated significantly with any geochemical forms.