A comparison of the availability of three zinc sources to maize (Zea mays L.) under greenhouse conditions

The objective of this study was to compare the availability of Zn from granular ZnSO4, a granular Zn humate-lignosulfonate (ZnHL), and liquid Zn ethylenediaminetetraacetate (ZnEDTA). The two granular sources were applied directly (as is) and also powdered and mixed with the soil. A calcareous sandy loam soil with low available Zn was used. Zn rates were 0, 4, 8, 16, and 32 mg pot(-1), and two crops of maize (Zea mays L.) were grown. For the first crop, all Zn sources provided an excellent dry matter response when powdered and mixed with the soil. The ZnEDTA was superior with regard to Zn uptake. The availability of ZnSO4 granules was almost zero for the first crop. The availability of the ZnHL complex was better than ZnSO4 when applied in granular form, but not when the two materials were powdered and mixed with the entire soil mass, suggesting that: availability differences between these sources were due to physical, not chemical, factors. After mixing with the soil, only small differences existed between the Zn sources for the second crop. All sources provided for a good dry matter and Zn uptake response, and all Zn sources were about the same in increasing diethylenetriaminepentaacetate (DTPA)-extractable Zn levels at the end of the experiment. This research suggests that the three Zn materials were equal long-term Zn sources, but that the shortterm response varied dramatically, depending on how the materials were applied.