Abstract
Salinity is one of the most common and critical environmental factors that limit plant growth and reduce crop yield. The aquifers, the primary sources of irrigation water, of south Florida are shallow and highly permeable, which makes agriculture vulnerable to projected sea level rise and saltwater intrusion. This study evaluated the growth responses of two ornamental nursery crops to the different salinity levels of irrigation water to help develop saltwater intrusion mitigation plans for the improved sustainability of the horticultural industry in south Florida. Two nursery crops, Hibiscus rosa-sinensis and Mandevilla splendens, were treated with irrigation water that had seven different salinity levels from 0.5 (control) to 10.0 dS/m in the experiment. Crop height was measured weekly, and growth was monitored daily using the normalized difference vegetation index (NDVI) values derived from multispectral images collected using affordable sensors. The results show that the growth of H. rosa-sinensis and M.splendens was significantly inhibited when the salinity concentrations of irrigation water increased to 7.0 and 4.0 dS/m, for each crop, respectively. No significant differences were found between the NDVI values and plant growth variables of both H. rosa-sinensis and M.splendens treated with the different irrigation water salinity levels less than 2.0 dS/m. This study identified the salinity levels that could reduce the growth of the two nursery crops and demonstrated that the current level of irrigation water salinity (0.5 dS/m) would not have significant adverse effects on the growth of these crops in south Florida.
Highlights
South Florida’s subtropical marine climate is conducive to growing a wide variety of subtropical and tropical ornamental crops year-round
The average relative growth rate (RGR) of H. rosa-sinensis and M. splendens substantially decreased when the salinity concentrations reached 7.0 and 4.0 dS/m, respectively, which could not be found in the visual assessment results (Figure 3)
The average RGR of H. rosa‐sinensis and M. splendens substantially decreased when the salinity concentrations reached 7.0 and 4.0 dS/m, respectively, which could not be found in the visual assessment results (Figure 3)
Summary
South Florida’s subtropical marine climate is conducive to growing a wide variety of subtropical and tropical ornamental crops year-round. Miami-Dade County ranks as the number one ornamental crop production area in Florida, with 76% of the total amount of ornamental crops produced commercially in the U.S [1]. These favorable environmental conditions are ideal for a high constant groundwater extraction that poses a challenge of saltwater intrusion into freshwater wells. The aquifer systems in Florida have been experiencing saltwater intrusion caused by sea level rise, leading to the contamination of wells for agricultural and domestic water supplies and changes in water management practices in south Florida [5,6,7]. The aquifers are shallow and highly permeable, making agriculture in south Florida very vulnerable to sea level rise and saltwater intrusion. In Miami-Dade County, 1640.5 million liters (c.f., 92.6 million liters from surface water sources) of freshwater are withdrawn from the aquifers each day, and irrigation water is taken from groundwater sources at a rate of 226.8 million liters (c.f., 24.9 million gallons from surface water sources) per day [8]
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