EFFECTS OF EXTRACTION PERIOD AND SOIL - SOLUTION RATIO ON THE AMOUNT OF ZINC EXTRACTED FROM SOILS BY DIFFERENT EXTRACTANTS

Investigations have examined the effects of extraction period and soil:solution ratio on the extraction of zinc from some New Zealand soils by EDTA, DTPA, Ha, Ca(NO3)2 and CH3COONH4. A high proportion of the zinc extracted by EDTA, DTPA, HCl, and Ca(NO3)2, was extracted rapidly, within the first 0.5 h, followed by small increases over the next 15 h. An exception occurred with a soil containing iron/manganese concretionary material. In this soil, with both EDTA and DTPA, there were significant increases in the amount of zinc extracted between 1 and 8 h. The amounts of zinc extracted by CH3COONH4 increased gradually with the time of extraction up to approximately 4 h. Substantial increases in the amounts of zinc extracted with HCl, Ca(NO3)2 and CH3COONH4 were obtained by increasing the soil:solution ratio from 1:2.5 to 1:10. However, soil:solution ratio has little effect on the amounts of zinc extracted by EDTA or DTPA.