The effect of residual Zinc and its chemical forms on growth and Zinc concentration of rice (Oryza sativa L)

Zinc deficiency has been reported for some crops in Iran. The published reports indicated that a considerable portion of applied has not been absor bed by the first plant and thus could be used by subsequent crops. The objectives of the present experiment were: the study of (i) The effects of residual Zn on growth and of rice Zn concentration and uptake by rice (Oryza sativa L.), (ii) the Growth and Zn concentration and uptake as affected by Zn chemical forms.Twenty surface soil samples (0-30cm) from major paddy rice fields in Fars province were used and treated with 3 levels of Zn (0, 5, 10 mg/kg soil as ZnSO4.7H2O) and other nutrient elements, then planted to rice (first crop). Pots after added all essential nutrients except Zn were replanted to rice (second crop) for 60 days. Shoot dry weight, relative growth and Zn concentration and uptake were used as plant responses. Soil samples taken before rice and Zn concentration were determined. In addition, chemical forms of native and applied Zn were determined by sequential factorial method.The results indicated that although residual Zn had no significant effect on dry matter of rice, it markedly increased Zn concentration and uptake by this crop. Furthermore, extractable Zn before the second crop determined by any of the three methods was higher than critical level. The results of present study showed that carbonate form is responsible for the observed residual effect of ZnSO4 in these calcareous soils Multiple regression equations revealed that the carbonate form was significantly correlated with Zn concentration and uptake in rice.