Biostimulants are a diverse group of substances that offer an environmentally friendly
alternative to plant protection products and improve plant tolerance to stress, as well as
crop quality. The aim of this study was to determine the effects of biostimulants on the
growth and development of seedlings of lettuce 'Joliac', cauliflower 'Faston F1', tomato
'Valido', and courgette 'Tempra F1'. The experiment was conducted in 2025 in a heated
greenhouse at the experimental field of the Department of Agronomy, Biotechnical
Faculty, University of Ljubljana, from 17 March to 20 May 2025. Four biostimulants
were used: Amalgerol, Protifert, Biimore, and Tonivit. The biostimulants were applied
twice in accordance with the manufacturer’s instructions, while the control treatment
received distilled water. When the seedlings reached marketable size, the following
parameters were measured: plant height, fresh and dry weight, SPAD values, leaf area,
and stem diameter. Based on these measurements, additional parameters were
calculated, including the Dickson Quality Index (DQI), shoot-to-root ratio (T/R),
specific leaf area (SLA), leaf weight ratio (LWR), root weight ratio (RWR), and stem
weight ratio (SWR). The results showed that plant responses to biostimulants depend on
both the plant species and the type of biostimulant applied. In some cases, biostimulants
significantly improved growth parameters, particularly seedling quality, as indicated by
higher DQI values and more favorable biomass distribution. The most pronounced
positive effect was observed in cauliflower, while the response in other species was less
evident or absent. Overall, the results confirm that biostimulants can enhance seedling
growth and quality; however, their effects are not universal and depend on plant species,
biostimulant composition, and application method.
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