IONIC PROPORTIONS OF THE NUTRIENT SOLUTION AND THEIR EFFECT ON MACRONUTRIENT EXTRACTION IN HYDROPONICALLY GROWN LETTUCE

Resumen

The nutrient solution (NS) consists of water with dissolved mineral ions, whose proportions depend on the species, cultivar, phenological stage, and environmental conditions, among other factors. This study aimed to evaluate the effect of variations in the proportions of NO₃⁻ and K⁺ in the Steiner nutrient solution on the extraction of macronutrients in lettuce grown in a closed hydroponic system. The treatments were as follows: T1 (control): original Steiner NS, with proportions of 9.000:0.750:5.250 molc m⁻³ for the anions NO₃⁻:H₂PO₄⁻:SO₄²⁻ and 5.250:6.750:3.000 molc m⁻³ for the cations K⁺:Ca²⁺:Mg²⁺; T2: 11.338:0.354:2.479 and 5.250:6.750:3.000 molc m⁻³; T3: 6.371:1.194:8.362 and 5.250:6.750:3.000 molc m⁻³; T4: 9.000:0.750:5.250 and 6.375:5.675:2.522 molc m⁻³; and T5: 9.000:0.750:5.250 and 3.158:8.743:3.886 molc m⁻³. Concentrations of N, P, K, Ca, and Mg were determined in leaves, buds, and roots, and together with dry biomass data, were used to estimate nutrient extraction per organ. The highest nutrient content was recorded in leaves (79 % of the total extracted). The greatest extractions corresponded to N and K, reaching 5.89 and 5.67 mg plant⁻¹, respectively, with T2 (high NO₃⁻ proportion). Increasing NO₃⁻ in the anionic proportion enhanced Ca and Mg uptake, whereas increasing K⁺ reduced the extraction of these same cations. Treatments T2 and T4 showed the highest total extractions, mainly due to the greater values of N and K obtained compared with treatments in which the proportion of these ions was reduced. These results indicate that modifications in the anionic and cationic proportions of the nutrient solution significantly influence nutrient extraction in lettuce, with the treatment containing the highest NO₃⁻ proportion being the most efficient for the uptake of N, K, Ca, and Mg.