EFFECTS OF IRON APPLICATIONS ON DTPA-EXTRACTABLE SOIL MICRONUTRIENTS

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Abstract
Effects of Fe sources, levels of added Fe, and incubation time on the availability of micronutrients in a slightly acid (normal) and a calcareous (Fe-deficient) soil were determined. Twenty, 40 and 80 ppm Fe, as Fe-EDDHA [iron-ethylenediaminedi(O-hydroxy)phenylacetic acid], Fe-PF [iron-polyflavonoid], and Fe-LS [iron-lignosulfonate] were mixed with soils and incubated at field capacity at room temperature. DTPA [diethylenetriaminepentaacetic acid] extraction of soil samples collected at 1, 2, 4 and 8 wk intervals indicated that, in general, proportional Fe recovery decreased with increasing Fe application. After 8 wk, Fe recovery from Fe-EDDHA applied to the normal soil at rates of 20, 40 and 80 ppm Fe was 46, 34 and 21%, respectively. Fe retention by the soil increased with time, and was higher in Fe-deficient soil than in normal soil. Iron-EDDHA was found to be the most stable compound in both soils. Iron-PF was more stable in Fe-deficient soil than Fe-LS, and the reverse was true in the normal soil. Extractable Mn increased with increasing Fe application. Extractable Zn and Cu varied with soil and source of Fe. Iron-LS produced the highest increase in extractable Cu and Zn; Fe-PF increased Mn, but Fe-EDDHA had little or no influence on extractable soil micronutrients. Fe-EDDHA has a superior efficiency to Fe-LS and Fe-PF in both soils. The results also confirm the suitability of DTPA as a soil extractant for available Fe.
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