Plant density to compensate for coriander production losses caused by the isolated and/or combined effects of salt and root-zone temperature stresses

Resumo

Hydroponics has represented an emergent solution for arid and semi-arid regions due to freshwater limitations, especially for promoting better plant growing conditions using brackish waters. Besides salt stress, the plants are exposed to other abiotic stresses, such as temperature, which may further enhance the salinity effect. Given the above, two experiments were conducted with coriander grown at different plant densities using an NFT (nutrient film technique) hydroponic system. The first experiment occurred from January to February by submitting plants to saline water produced with salts of different cationic natures, and the second was from October to November using the same water (only NaCl) combined with different root-zone temperatures (RZTs), both in 2021. Experiment I included the control (electrical conductivity of water – ECw of 0.25 dS m^-1) and six other treatments with ECw of 6.50 dS m^-1 obtained by dissolving NaCl, KCl, MgCl₂, CaCl₂, NaCl + CaCl₂ + MgCl₂, and NaCl + CaCl₂ + KCl. Experiment II combined two ECw levels (0.25 and 6.50 dS m^-1) with three RZTs (ambient – ARZT, ARZT + 2°C, and ARZT + 4°C, corresponding to the mean values of 28.80, 30.64, and 32.59°C). Both experiments distributed five plant densities (6, 12, 18, 24, and 30 plants bunch^-1) in subplots in the hydroponic channel (main plot). Using water with a high salinity level (ECw 6.50 dS m^-1 with salts of different cationic natures) allowed coriander cultivation, except for MgCl₂, which led to higher production losses. Higher number of plants (density of 30 plants) compensated for production losses due to the stress, with yields comparable to those without salt stress at the lowest density of 6 plants. Experiment II partially confirmed this compensation, provided RZT would not exceed 30.64°C when using saline water (ECw 6.50 dS m^-1) for production.