Impact of the Hydroponic Cropping System on Growth, Yield, and Nutrition of a Greek Sweet Onion (Allium cepa L.) Landrace

Abstract

Nerokremmydo of Zakynthos, a Greek landrace of sweet onion producing a large bulb, was experimentally cultivated in a glasshouse using aeroponic, floating, nutrient film technique, and aggregate systems, i.e., AER, FL, NFT, and AG, respectively. The aim of the experiment was to compare the effects of these soilless culture systems (SCSs) on plant characteristics, including fresh and dry weight, bulb geometry, water use efficiency, tissue macronutrient concentrations, and uptake concentrations (UC), i.e., uptake ratios between macronutrients and water, during the main growth, bulbing, and maturation stages, i.e., 31, 62, and 95 days after transplanting. The plants grown in FL and AG yielded 7.87 and 7.57 kg m−2, respectively, followed by those grown in AER (6.22 kg m−2), while those grown in NFT produced the lowest yield (5.20 kg m−2). The volume of nutrient solution (NS) consumed per plant averaged 16.87 L, with NFT plants recording the least consumption. The SCS affected growth rate of new roots and “root mat” density that led to corresponding nutrient uptake differences. In NFT, reduced nutrient uptake was accompanied by reduced water consumption. The SCS and growth stage strongly affected tissue N, P, K, Ca, Mg, and S mineral concentrations and the respective UC. The UC of N and Κ followed a decreasing trend, while that of Mg decreased only until bulbing, and the UC of the remainder of the macronutrients increased slightly during the cropping period. The UC can be used as a sound basis to establish NS recommendations for cultivation of this sweet onion variety in closed SCSs.