Physiological, nutritional and growth responses of melon (Cucumis melo L.) to a gradual salinity built-up in recirculating nutrient solution

Minimizing salinity impacts on yield in melon crops cultivated in closed-loop hydroponic systems requires better understanding of the physiological impact of gradual salt accumulation in the recycled solution. To attain this objective, different sodium chloride (NaCl) concentrations in the irrigation water, i.e. 0.7, 2.5, and 5mM, were applied in two cropping seasons (winter-spring;WS and spring-summer;SS). In both seasons plant biomass and yield were negatively affected only in high NaCl-treated plants, due to stomatal limitations, which restricted carbon dioxide (CO2) diffusion into the leaf, osmotic and salt-specific effects. However, a progressive NaCl built-up to maximum concentrations in the root zone solution of 15 (WS) and 20mM (SS), enabled plants to preserve several physiological mechanisms, thereby adjusting growth and yield without impairing fruit quality. Our results suggest that the use of irrigation water, containing up to 2.5mM NaCl, is feasible in melon crops grown in closed-loop hydroponic systems, without yield and quality losses.