Effect of Phosphatic Fertilization on Zinc Adsorption in Some Vertisols and Inceptisols

The effects of temperature, sources of Zn and incubation time on the availability of zinc in sodic soils was studied in laboratory. The soil Zn was extracted first with DTPA and then with NH4OAc from the same samples. DTPA extractable as well as NH4OAc extractable Zn was higher in 70 ESP soil followed by 30 ESP and then 5 ESP soil. After addition of Zn through Zn-EDTA. ZnSO4 and Zn3(PO4)2 there was always more DTPA and NH4OAc extractable Zn than in control. Similarly 25 ppm Zn treated samples showed always more Zn than 10 ppm Zn treatment. Zn-EDTA treated samples gave more Zn than ZnSO4 and Zn3(PO4)2 treated samples. With longer incubation time, both forms of Zn decreased, more so in Zn-EDTA and Zn SO4 treatments. In Zn3(PO4)2 treatments, extractable Zn generally increased after 7 days of incubation. Higher temperature (40°C) treatments gave more fixation and less release of both forms of Zn as compared to 20° C treatment from Zn-EDTA and ZnSO4 but in Zn3(PO4)2 treated samples, more Zn was released at higher temperature (40°C). At both the temperatures, however, Zn continued to decrease with longer incubation time.