Response of hydroponic lettuce to aeration, nitrate and potassium in the nutrient solution

Abstract

Purpose: Floating hydroponic system for lettuce greenhouse production consists of plants inserted in styrofoam platform floating in a 15 cm-tall nutrient solution, which is aerated by some growers while others maintain the solution static. The present investigation had the objective of determining the effect of ${\rm NO}_3^-$-N and K in Romaine lettuce cultivated in floating hydroponic system and the impact of nutrient solution aeration. Materials and methods: Plants were transplanted into 34 L rigid plastic containers with aerated or non-aerated solutions containing either 15/7, 12/8.5 or 12/2.85 meq L−1 of ${\rm NO}_3^-$/K concentration. Results: Aeration of the nutrient solution promoted plant growth, leaf K, P, and Mg, and water uptake, however, photosynthesis and transpiration rates were enhanced under non-aeration conditions. Decreasing N did not affect leaf N uptake and accumulation; however, decreasing K markedly decreased leaf P and K in aerated plants. Despite the higher transpiration and stomatic conductance in non-aerated plants, water uptake was higher in aerated plants. Non-aerated plants exhibited decreased leaf K accumulation. Conclusions: non-aeration or reduction of K concentration of the nutrient solution may be a strategy to reduce leaf K in lettuce; leaf N concentration was unaffected by aeration.

Keywords

• lactuca sativa
• floating hydroponic system
• leafy vegetables
• photosynthesis rate
• water uptake