Interactive Effects of NaCl Levels and Zinc Sources and Levels on the Growth and Mineral Composition of Rice

The effects of sodium chloride and Zn rates and sources on the growth and chemical composition of lowland rice (Oryza sativa L.) were studied using calcareous soil in a greenhouse experiment. The treatments comprised 5 levels of NaCl (0, 12.5, 25, 37.5 and 50 mmol kg-1 soil), three Zn rates (0, 5 and 10 mg kg-1 soil) and two Zn sources (ZnSO4, 2H2O and ZnEDTA). Applied salinity decreased shoot dry weight, leaf area and chlorophyll concentration, whereas Zn supply significantly increased these growth parameters.However, the enhancing effect of soil Zn fertilization was more pronounced at lower NaCl levels than under higher salt stress, irrespective of Zn sources. Concentrations of Zn, P and K were significantly decreased and those of Na and Cl increased in NaCl-treated plants. Zn application markedly increased Zn concentration and decreased Na and Cl and P accumulation in shoots. Moreover, there was a significant difference between the two Zn sources to affect rice growth. Free proline increased but reducing sugars decreased with an increase in the levels of substrate NaCl. However, Zn-untreated rice contained higher proline and reducing sugars than Zn-treated plants. Furthermore, an increase in proline was greater in the presence than in the absence of Zn and with ZnSO4 than with ZnEDTA. It is concluded that a decrease in soil osmotic potential, nutrient imbalance and excessive plant accumulation of Na and Cl in NaCl-treated plants caused growth suppression, whilst Zn supply decreased the suppressing effects of excess salt on rice growth. Therefore, it is recommended that for growing rice in saline soils that are low in available Zn, Zn should be supplied in a adequate quantities