A comparison of zinc sources and extraction methods on sandy soils suitable for maize cropping

Maize is the most important crop produced for human and animal nourishment in South Africa. The crop is susceptible to zinc (Zn) deficiencies, which result in lower grain yields with poorer nutritional value. Knowledge of the nature and behaviour of Zn fertilisers is therefore important for sustainable maize production, especially in sandy soils. The aim of this incubation study was to test the effect of inorganic (ZnO, ZnCl2, ZnCO3 and ZnSO4) and chelated (ZnEDTA, ZnDTPA, ZnEDDHA and ZnHEDTA) sources of Zn applied at different rates on Zn extracted by diluted HCl, DTPA, Mehlich-1, Ambic-2 and Na2EDTA methods. Analyses showed that ZnO was the least effective source, and ZnSO4 was the most effective source at increasing the extractable Zn of sandy soils. The extractable Zn content of the soils increased almost linearly with increasing application rates of all the zinc sources. Generally, the Na2EDTA method was most efficient in extracting the applied Zn. These results must be validated with crop growth response in glasshouse and especially field studies.