Evaluation of Some Chelates in Estimating Available Zn for Soybean in Calcareous Soils

AbstractSix fertilizer trials on calcareous soils in Saudi Arabia were conducted for the prediction of Zn deficiency in soybean (Glycine max L., var Merr). Zinc level before planting was tested by using 3 different extractants, i.e. DTPA, AB‐DTPA and EDTA. Zinc was applied in the form of ZnSO4 · 7H2O at 0, 5, 10, 15, 20 and 40 kg Zn ha−1. Plant samples were taken at early bloom and tissue was analysed for Zn. Two methods were used to judge the critical deficiency level of Zn: Cate‐Nelson and chisquare models.The critical level estimated according to the Cate‐Nelson method for DTPA extractable soil Zn was 0.43 mg kg−1 in the growing season 1991. EDTA gave a much higher level (1.80 mg kg−1) and AB‐DTPA gave an intermediate level (0.68 mg kg−1). Chi‐square statistical procedure gave a very similar critical level of 0.66 mg kg−1 for AB‐DTPA but lower for either DTPA (0.38 mg kg−1) or EDTA (1.32 mg kg−1). The critical level based for three growing seasons ranged from 0.25 to 0.68, 0.32 to 0.82 and 1.12 to 3.4 mg Zn kg−1 for DTPA, AB‐DTPA and EDTA extractants, respectively.The values obtained by the linear regression equation with soybean leaf concentration were 0.45 and 0.70 mg Zn kg−1 for DTPA and AB‐DTPA, respectively. Such values are very close to those determined by using the Cate‐Nelson method. On the other hand, the value obtained for EDTA (1.15 mg Zn kg−1) was comparatively lower than that calculated by applying the Cate‐Nelson method.