CHANGES IN FRACTIONS OF SOME MICRONUTRIENTS AS AFFECTED BY CONTINUOUS CROPPING AND LONG-TERM APPLICATION OF MINERAL AND ORGANIC FERTILIZER.

Soil samples were collected from on-going long-term experiment at Bahtim area, Kalubia Governorate, Egypt, to study the distribution of various forms of iron, manganese, zinc and copper. The optimum dose-based treatments selected for the study were N(15kg/ fed), N(15kg/fed)-P, N(15kg/ fed)-P-K,N(30kg/fed),N(30kg/fed)-P,N(30kg/fed)-P-K,N(60kg/fed), N(60kg/fed)-P, N(60kg/ fed)-P-K, organic (FYM), and control (no fertilizer or manure). Differnet fractions of Fe, Mn, Zn and Cu in the soil were sequentially extracted using different extractants. DTPA- extractable Fe, Mn, Zn and Cu in soil increased in all treatments compared to control as a result of continuous cropping and fertilizer application. The amount of Fe, Mn, Zn and Cu in different fractions revealed the following order: exchangeable ˂ organically bound ˂ manganese oxides ˂ crystalline iron oxides ˂ amorphous iron oxides˂ residual. DTPA-Fe showed significant correlations with all Fe fractions except manganese oxides-Fe. DTPA- Mn showed significant correlations with all Mn fractions except crystalline iron oxides- Mn. DTPA- Zn showed significant correlation with all fractions of Zn except both exchangeable and organic matter- Zn. As for, DTPA- Cu results showed a significant correlation only with organic matter- Cu.