Mineral nutrients needs of cucumber and its yield in protected winter cultivation, with HPS and LED supplementary lighting

Abstract

The objective of the study was to evaluate yield, mineral nutrients uptake and nutrient demands of cucumber plants in winter cultivation with HPS and LED supplementary lighting. The experiment was carried out in the three variants: 1) HPS - top light only; 2) HPS + LED - top light + 2 lines of LED inter-row light; 3) LED + LED - top LED + 2-line LED inter-row light. In these variants the same PAR intensity level, of about 320 μmol m−2 s−1 (PPFD), was provided. Midi-cucumber parthenocarpic cultivar ‘Svyatogor’ F1, of high shade tolerance and 18–22 cm fruit lenght, was grown for 17 weeks during winter, in mineral-rock slabs. The plants were trained on a single stem up a string, according to the ‘high wire system’ method. Number and weight of every-day harvested fruit were determined. On the basis of monitoring, content of macro- and micro-elements in drip and drain solutions that was undertaken during every two-week period and constant monitoring of total daily drip irrigation quantity with nutrient solution per one plant, as well as total daily drain of the nutrient solution, the daily uptake of nutrient solutions and nutrients per one plant was calculated. The nutrient status of the plants was determined by leaf samples analysis performed for the younger, upper 3rd–5th leaves, as well as for the older, 10th–12th, lower leaves. Cucumber plants were characterized by stable yield and showed high fruit yield of very good quality. The highest yield was found for the plants grown with supplementary lighting with LED + LED. Leaves from the plants grown with the standard HPS top lighting showed faster senescence than the leaves of the plants grown with inter-row lighting. This is evidenced by a higher concentration of Ca, Mg, S, Mn and B ions, together with a lower concentration of K ions, in 10th–12th leaves in the plants grown with the standard HPS top lighting, compared with the plants grown with the HPS + LED lighting, as well as with the LED + LED lighting. The plants grown with the inter-row lighting showed a higher nutritional demands than the plants grown with the standard HPS top lighting. Parallelly used LED top lighting resulted in a higher and more stable yield, compared to standard HPS lighting conditions.