Changes with time of zinc forms in an acid, a neutral, and a calcareous soil amended with three organic zinc complexes

Three zinc (Zn) fertilisers were added as soluble organic salts (Zn-ethylenediaminetetraacetate plus fulvic and humic acids, Zn-lignosulfonate plus ethylenediaminetetraacetate, and Zn-2-hydroxy-1,2,3-propanetricarboxilate) at several levels, to 3 representative types of soils, to study the behaviour of Zn applied. Samples of treated and untreated soils were incubated for 15, 30, and 60 days at 22˚C and field capacity. A selective sequential dissolution procedure and DTPA extraction were employed to determine the changes in Zn distribution. The distribution and the percentage conversion into different forms of the added metal were dependent on soil type, Zn sources, and Zn loading level. After an initial increase in all forms of Zn in the treated soils, Zn concentration in the water-soluble plus exchangeable fraction and the amounts extracted with DTPA began to decrease. At the end of the experiment, Zn in the most labile fraction was detected in the calcareous soil (pHw 8.3) only when the mixture of fulvic and humic acids with Zn-EDTA chelate was applied (e.g. 1.59 mg/kg of Zn in the 20 mg/kg treatment). The highest conversion values of Zn applied in this calcareous soil occurred in the amorphous Fe-oxide bound and residual fractions of all fertilisation treatments and a low conversion value occurred in the carbonate-bound fraction. <keyword>fulvic acid, humic acid, Zn-EDTA, Zn-lignosulfonate, Zn-2-hydroxy-1,2,3-propanetricarboxilate, Zn extractability.</keyword>