In order to investigate the effect of zinc, iron and manganese fertilization on Zn, Fe and Mn concentrations in the stem and leaves and on the chlorophyll content in leaves of soybean at different reproductive growth stages, two experiments were conducted on a research field of the Islamic Azad University of Kermanshah, Iran, during the 2010 and 2011 growing seasons. The experimental design consisted of a factorial experiment based on the randomized complete block method with three replicates. The treatments included three levels of Zn (0, 20 and 40 kg ha-1), Fe (0, 25 and 50 kg ha-1), and Mn (0, 20 and 40 kg ha-1), all applied to soil. At 30, 60, 90 and 120 days after sowing (DAS), the SPAD readings were done on five leaves from each experimental plot for all replicates. Five plants were randomly selected from each plot at the flowering, pod setting, seed filling and maturity stages. Samples washed with distilled water were dried, weighed and incinerated at 550°C. Finally, the Zn, Fe and Mn concentrations were determined by Atomic Absorption Spectrometry. The results indicated that zinc application had significantly affected Zn, Fe and Mn concentrations in soybean stems at all the sampling times except for the soybean stem Mn concentration at the maturity stage. In contrast, the concentration of Mn at seed filling was unaffected by iron fertilization. Also, the maximum Fe concentration in soybean stems resulting from zinc application was achieved in Zn20 treatment. The highest Zn and Mn concentrations in leaves were recorded when iron was applied in smaller amounts. Furthermore, zinc, iron and manganese applications had significant effects on the leaf chlorophyll concentration during all the growth stages of soybean plants. In addition, increased iron and manganese fertilization raised the soybean leaf chlorophyll concentrations in all the samples. The maximum chlorophyll concentration in soybean leaves at 60 DAS was recorded in Zn20Fe50, Zn20Mn40 and Fe50Mn40 treatments (34.7, 34.0 and 35.2, respectively).

21.2.2016