Coastal agriculture frequently relies on surface water for irrigation. However, in Florida, surface water availability can become limited during the dry season, leading growers to switch to groundwater. Groundwater in coastal areas often contains high salt concentrations which can negatively affect crop production. Citrus species, one of the most cultivated crops in Florida, are sensitive to salt stress. Among other strategies, irrigation management is used to mitigate salinity buildup in soil by leaching salts away from the root zone. Increased irrigation rates with water sources in the ‘slight’ to ‘moderate’ range of salinity (0.7 to 3 dS/m) have been shown to reduce salt accumulation in the soil without affecting production. However, when the water has high salinity concentrations (>3 dS/m), increasing the irrigation rate beyond 125%-130% of the crop evapotranspiration (ETc) is not sustainable due to the high-water usage. Conversely, a limited volume of water applied for leaching the salts can exacerbate the accumulation. In coastal Florida, where often only high salinity water is available during the dry season, evaluating short-term strategies to maintain crop production is crucial. The objective is to understand how irrigation water with high salinity concentrations and different irrigation rates impact plant performance and soil salinity accumulation. In this study, one-year-old ‘Ruby Red’ grapefruit trees grafted on ‘US-942’ rootstock were planted in a weighing lysimeter phenotyping platform (“Plant Array”) under greenhouse-controlled conditions. Irrigation water with high salinity concentration (5 dS/m) was precisely applied at three different irrigation rates: 75% (deficit), 100% (regular), and 125% (excessive) of the ETc. A control treatment with water at a low salinity concentration (0.3 dS/m) was applied at 100% ETc for comparison. Transpiration, plant net weight, soil moisture and soil electrical conductivity (EC) were recorded daily. Bulk leaf water potential, osmotic potential, and dark-adapted chlorophyll fluorescence were measured at the beginning and at the end of the experiment. Results showed that ETc and net weight decreased for those plants irrigated with high salinity concentration compared to the control. Salt EC was higher for those trees irrigated with 75% ETc under high salinity concentration resulting in the lowest ETc rates. Plants irrigated with 100% and 125% ETc rates showed similar results, likely due to decreasing transpiration of trees upon high salinity treatment application. Different plant performance under different irrigation rates emphasized the need of evaluating irrigation strategies in mitigating salt stress in citrus, particularly in region with limited water resources.
