EFFECT OF ANALYTICAL PARAMETERS ON THE PR ECISION OF SOIL ZINC EXTRACTION METHODS

Fifteen soil samples and four extractants (DTPA, Na(2)EDTA, HCl and Me hlich 1) were used to study soil extraction methods for available zinc . Each extractant was studied in three soil:solution ratios (1:2, 1:4 and 1:10) and in three extraction periods in the ratio most frequently used. The zinc extracted by DTPA, Na(2)EDTA and HCl was not affected by use of soil:solution ratios 1 :2 and I :4, but the amount extracted increased with the 1:10 ratio. In this relation, the variation coeffi cients increased. With Mehlich, no definite tendency was observed. The increase of extraction period for DTPA extractant, in 1:2 ratio, had little effect on the amount of zinc extracted and on the precision. As to Na(2)EDTA extractant in I:10 ratio, with the increase of extractio n time, both increased. As to HCl and Mehlich, both in 1:4 ratio, the increase in extraction period had no effect on the amount of zinc extr acted and no definite effect on the precision. Thus, the use of 1:2 ra tio for DTPA and Na(2)EDTA and 1:4 ratio for acid extractants is recom mended. Concerning the period of extraction, 120 min should be used wi th DTPA and Na(2)EDTA, 15 min with HCl and 5 min with Mehlich.