Soilless Cultivation System, Electrical Conductivity of Nutrient Solution, and Growing Season on Yield and Quality of Baby-Leaf Oak-Leaf Lettuce

Giulia Conversa,Corrado Lazzizera,Anna Bonasia,Antonio Elia

doi:10.3390/agronomy11061220

Abstract

The floating system (FL) is a common soilless method for baby-leaf production, whereas the ebb and flow system (EF) has been proposed as an alternative. Both of them allow managing plant saline stress while preventing reduction in plant growth and yield and increasing product quality. The oak-leaf lettuce response to the growing conditions (hydroponics, salinity) in interaction with climate and genotype has been little studied. Two experiments were carried out with two oak-leaf cultivars (green- and red-colored type) grown in FL and EF systems at two levels of nutrient solution (NS) electrical conductivity (EC) (EC = 2.5 and 3.5 dS m−1; EC2.5, EC3.5, respectively) under autumn and late-spring conditions. The EF system caused an increase in salinity in the substrate where roots mainly develop, so it overcomes the effect of the EC3.5 treatment. In the autumn cycle, irrespective of the EC, EF-grown plants had improved leaf thickness (specific leaf area), color, and antioxidative (total phenol and carotenoid contents) properties; however, a reduction in yield was observed in the most productive cultivar (green type). In late spring, higher yield and product quality (processability, nitrate content) were obtained at the expense of color, with the FL showing the best productivity in the green type cultivar. The red type cultivar had higher dry mass, phenol, and carotenoid concentrations.

Highlights

The baby-leaf category is important among the leafy vegetables
The ebb and flow system (EF) system caused an increase in salinity in the substrate where roots mainly develop, so it overcomes the effect of the EC3.5 treatment
Higher yield and product quality were obtained at the expense of color, with the floating system (FL) showing the best productivity in the green type cultivar

Summary

Introduction

The baby-leaf category is important among the leafy vegetables. It is harvested at an early-vegetative phase (8–12 cm in length), the name, and it includes many species, with Lactuca sativa L. among the most popular [1]. Other types of lettuce such as oak-leaf with attractive colors and shapes are produced as baby-leaf to combine the best quality characteristics from all varieties [2] They are mainly used as minimally processed vegetable products [3] and consumed in increasing amounts as they provide an important source of health-promoting compounds such as carotenoids, vitamin C, and polyphenols [4,5,6]. Some concerns have arisen about this system as it is static (with no recirculation of NS), and a lack of oxygen frequently occurs in the NS, especially at high temperatures [3], so farmers are forced to provide continuous oxygen enrichment of the NS To cope with this potential limit, the ebb and flow system (EF) can be used as an alternative for growing baby-leaf vegetables as it allows better root oxygenation deriving from the periodical NS supply to the root through sub-irrigation. The information available on the effect of EF is mainly focused on vegetables other than lettuce [9,10,11,12], while the only published study on this species involves the romaine morphotype [13]

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