The Effect of Salinity on the Growth and Nutrient Status of Zinnia Grown Under Regulated Deficit Irrigation

As fresh water resources become more limited agricultural producers will have to consider alternative, often poor quality, water sources for irrigation. Impurities such as salinity in water can impact irrigation management practices and adversely affect crop yield. To test the effects of salinity on plant growth and nutrient composition, Zinnia eleganswas produced under two different sub-irrigation management regimes and exposed to various concentrations of NaCl to simulate the crop production challenges associated with poor water quality. Plants were irrigated for a short- or long-cycle of exposure in sub-irrigation to achieve differing levels of potting medium saturation at each irrigation event. Plants under these two irrigation management regimes were challenged with NaCl at concentrations up to 1.5 g/L.  Zinnia plants accumulated more Na in shoot tissues as the NaCl concentration in the irrigation water increased. The electrical conductivity in the potting medium also increased over time as the NaCl concentration in the irrigation water increased and the rate of leaf area expansion decreased with increasing levels of salinity. Fertilizer and water use efficiency have both been reported to increase under regulated deficit irrigation practices such as short-cycle irrigation management. In our study, plants under short-cycle sub-irrigation management maintained lower gravimetric water content throughout the production cycle compared to plants under long-cycle sub-irrigation but the drier medium conditions did not increase susceptible to salt injury. Further, plants grown under short-cycle irrigation management for 4 to 6 weeks accumulated less Na in shoot tissue than plants grown under long-cycle irrigation management. Sodium accumulation in the shoot tissues was a product of both the amount of sodium in the irrigation solution and the amount of water used by the plant over time. Therefore short-cycle irrigation can be used as an effective water management technique even when raw water quality is poor as represented by elevated salinity. Our research indicates that zinnia can be irrigated with saline water up to 0.5 g/L in a 4- to 6-week production cycle without adverse effects on growth.