In this study, maize (Zea mays L. cv. Norma SC) and sunflower (Helianthus annuus L. cv Arena PR) seedlings treated by molybdenum (Mo) that were cultivated in special plant growth boxes, known as rhizoboxes. During our research we tried to examine whether increasing molybdenum (Mo) concentration effects on the dry mass and absorption of some elements (molybdenum, iron, sulphur) of shoots and roots of experimental plants. In this experiment calcareous chernozem soil was used and Mo was supplemented into the soil as ammonium molybdate [(NH 4 ) 6 Mo 7 O 24 .4H 2 O] in four different concentrations as follow: 0 (control), 30, 90 and 270 mg kg -1.
In this study we found that molybdenum in small amount (30 mg kg -1 ) affected positively on growth of maize and sunflower seedlings, however, further increase of Mo content reduced the dry weights of shoots and roots. In case of maize the highest Mo treatment (270 mg kg -1 ) and in case of sunflower 90 mg kg -1 treatment caused a significant reduction in plant growth. In addition, we observed that molybdenum levels in seedling were significantly elevated with increasing the concentration of molybdenum treatment in comparison with control but the applied molybdenum treatments did not affect iron and sulphur concentration in all cases significantly.