In hydroponic cultivation of vegetables with a solid substrate, mineral wool predominates. The pro-ecological policy and consumers’ expectations cause an increase in interest in organic substrates, which, when properly used, are less harmful to the environment. The aim of this study was to determine the effect of reusing lignite substrate in hydroponic cultivation on the growth, yield and quality of cucumber fruit and on the physical parameters of the substrate. The greenhouse cucumber cultivar ‘Mewa F1’ with semi-long fruits and smooth skin was used for the study. The plants were grown in the ‘Carbomat’ lignite substrate and ‘Grotop Master’ rockwool in two cycles. In cycle 1, new growing mats were used, while in cycle 2 the same growing mats as in cycle 1 were used again. In the hydroponic cultivation carried out on mineral wool and in the lignite substrate, both in the new and the reused substrate, the cucumber obtained mostly similar plant growth parameters and fruit color. Cucumber grown on the new mineral wool had a higher number and weight of fruits, which were characterized by a higher content of β-carotene and lutein compared to fruits from plants grown in the new lignite substrate. On the other hand, the reused lignite substrate resulted in higher cucumber yields and fruits with higher firmness and higher carotenoid content compared to cucumber grown on reused mineral wool. At the same time, the content of dry matter and sugar extract in fruits obtained from plants growing in the new and reused lignite substrate was higher compared to fruits grown in mineral wool. Both new and reused lignite substrate were characterized by very low plant-available water content. In contrast; the air and water holding capacity of lignite after cultivation did not change as much as that of mineral wool.

Hydroponic cultivation using organic, fully biodegradable substrates that provide the right physical properties for plant growth and development is now the future of soilless production. Despite the high productivity and strict control of production conditions in this method, excessive salinity of the substrate often occurs. However, recent research results indicate that salinity at a high enough threshold can improve yield quality, while prolonged exposure to too high EC, or exceeding the safe EC threshold for a given species, leads to reduced quality and reduced or even no yield. The aim of this study was to determine the effect of biodegradable lignite substrate (L) and eustressor in the form of high EC nutrient solution (7.0 dS·m⁻¹) on morphological and physiological parameters, as well as the quality and yield of cucumber (Cucumis sativus L.) in hydroponic cultivation compared to the mineral wool substrate (MW). The MW/high EC combination showed a significant reduction in shoot diameter by nearly 6% compared to the MW/control EC combination. The stomatal conductance (g_s) and the transpiration rate (E) were also significantly reduced in this combination. The present study indicates that the effects of eustressor application vary depending on the growing medium used, and more favorable effects in terms of yield quality were obtained using biodegradable lignite substrate. The high EC of nutrient solution combined with lignite substrate (L/high EC) significantly increased in cucumber fruit the content of β-carotene, lutein, chlorophyll a, chlorophyll b and the sum of chlorophyll a + b by 33.3%, 40%, 28.6%, 26.3% and 26.7%, respectively, as compared to MW/high EC combination.

Environmentally friendly substrates that are biodegradable may provide an alternative to mineral wool, which is commonly used in hydroponic growing technology. Little is known about the relationship between the physical characteristics of lignite substrate and cucumber yield. The study analyzed the effect of bulk density and water holding capacity of lignite substrate in comparison to mineral wool and EC of nutrient solution on plant morphological parameters, yield and fruit quality of greenhouse cucumber. A positive relation was found between the bulk density of lignite mats and the increase in the number of leaves per week, shoot diameter as well as leaf length and leaf area (calculated as the product of leaf length × width) in cucumbers grown in this medium. Bulk density of lignite growing mats also affected the macro- and micro-nutrient content of cucumber leaves. The physical properties of the substrate and the high EC of the medium had a significant effect on the hardness, color and lutein content of cucumber fruits. The content of biologically active compounds in cucumber fruits depended on the water holding capacity of the medium and the water readily available to plants; these parameters were lower in the lignite medium compared to mineral wool. However, when the lignite substrate was used in hydroponic cucumber cultivation, for a period of 51 days after planting (DAP) there was an increase of more than 23% in the bulk density of the substrate and an increase of nearly 55% in the water readily available compared to the new lignite mats.

It was found that the taste and quality of tomato fruit can significantly depend on the cultivar, growing conditions, fruit maturity stage, and post-harvest treatments. This study aimed to compare the effects of growing conditions, such as the use of diffusion glass and LED supplementary light (LED+D), with diffusion and standard glass and HPS lamps (HPS+D; HPS) on the quality and post-harvest shelf life of pink tomato fruit cv. ‘Tomimaru Muchoo F1’ in relation to fruit maturity stage and storage temperature. Fruits were harvested at three ripening stages – mature green (MG), breaker (B) and fully ripe (FR). Fruits of each maturity stage were stored under controlled conditions in a cold store at 12 °C for MG and B fruits and at 6 °C for FR fruits (at 85% relative humidity), and 20 °C for all ripening stages (at about 50% relative humidity). Physiological weight loss, dry weight, hardness of fruit, fruit color ( L*, a*, b*, a*/b*), total soluble solids, total sugars, ascorbic acid, titratable acidity, pH, lutein, lycopene, a-carotene, b-carotene were determined. Pink tomato fruits harvested from LED-lighted plants in combination with diffusion glass showed the highest shelf life and post-harvest quality compared to fruits from HPS-lighted plants and HPS-lighted crops in combination with diffusion glass. Stored pink tomato fruits from the LED+D combination were characterized by significantly higher total sugars, vitamin C and β-carotene content than fruits from the combination HPS and HPS+D. Tomato fruits, regardless of the maturity stage, at 20 °C had higher fresh weight loss and lower fruit firmness during storage compared to those stored at lower temperatures. Pink tomato fruits stored in higher temperature colored faster and contained a higher concentration of components such as total soluble solids or ascorbic acid and carotenoids.