Residual Effect of Synthetic Zn Chelates On the Availability of This Metal In Different Soils Under Waterlogged Conditions.

Adding Zn improves crop growth, increases seed yield and also positively affects nutritional quality. After Zn fertilization, there is normally a period of several years in which residual effects provide an adequate supply of Zn to successive crops. Immediately after the application of Zn sources water-soluble Zn slowly but continually decreases. Various factors, including time and moisture conditions, affect the aging process and modify the solubility of the metal in soil and therefore its availability. The present study was undertaken to verify variations in the residual effects of applying four different synthetic Zn sources (Zn-EDTA, Zn-HEDTA, Zn-EDTA-HEDTA and Zn-DTPA-HEDTA-EDTA) at different rates of application [0 (control), 5 and 10 mg Zn kg^-1 soil] after three crops grown in two different soils (Soil 1: Typic Haploxeralf; Soil 2: Typic Calcixerept). The experiment was conducted to determine the concentration of Zn in the soil solution and the available Zn (estimated by the DTPA-TEA and LMWOAs methods) and their respective evolutions over experimental time (15, 45 and 75 d) under waterlogged conditions. In Soil 1, the Zn-EDTA fertilizer produced the highest Zn concentration in the soil solution and greatest quantity of available Zn. However, the Zn concentrations did not show any significant differences for any treatment over time. In Soil 2, the Zn-DTPA-HEDTA-EDTA produced the highest Zn concentration in the soil solution and the greatest quantity of available Zn. Applying this fertilizer, at both of the rates studied, produced significant differences over experimental time (P < 0.05) in the soil solution and also in terms of the amount of available Zn extracted with the LMWOAs method. In Soil 1, the soil solution exhibited acidic pH values ranging from 4.91 to 5.56. In Soil 2, the pH values were almost neutral or weakly alkaline and ranged from 7.00 to 7.42. For both soils, except in the control treatments, the available Zn concentrations obtained for the different Zn treatments were higher than those reported as critical for most plants. These concentrations were greater in Soil 1 than in Soil 2 and this was particularly evident at the high-rate of application.