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

Christos Mouroutoglou,Dimitrios Savvas,Anastasios Kotsiras,Georgia Ntatsi

doi:10.3390/horticulturae7110432

Christos Mouroutoglou, Dimitrios Savvas + Show 2 more

Open Access

https://doi.org/10.3390/horticulturae7110432

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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.

Highlights

The mean root zone temperature of the water culture systems climaxed above 32 ◦ C after 76 days after transplanting (DAT), while mean maximum root temperature of the same systems exceeded 32 ◦ C, after 20 days, with floating system (FL) presenting the least fluctuation
The differences in the shape index and sphericity of early bulbs observed in FL and aggregate systems (AG) (Figure 6e,f) can be attributed to the higher rate of swelling compared to the rate of elongation of the leaf base, which favored growing in diameter rather than in height
The uptake concentrations (UC) of S in AG recorded the largest increase between the compared closed soilless culture systems (CSCS) during the maturation period (Figure 8f). This increase indicates the production of structural proteins, which need S-containing amino acids to be biosynthesized [102]. It appears that Nerokremmydo of Zakynthos, a Greek intermediate day-length big-bulb variety of mild onion, adapts well in CSCS which eliminate soil problems and nutrient pollution of groundwater, and enhance yield

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Onion (Allium Cepa L.) is the second most important vegetable crop after tomato, showing a doubling of production since 2000. 99.9 Mtons of dry bulbs [1]. Modern paradigms of open-pollinated bulb onion landraces are Kremmydi Thespion [2], Cipolla di Giarratana [3] and Jaune des Cévennes [4] and Nerokremmydo of Zakynthos (meaning “an onion that needs plenty of water”), originating from a Greek

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