A Case Study of Allelopathic Effect of Parsley, Dill, Onion and Carrots on the Germination and Initial Development of Tomato Plants

Vegetables are important worldwide, but their production faces many problems. One of them is the yield decline due to soil sickness, allelopathic effects of other crops, weeds and trees, and also the autotoxicity when grown continuously for several years. For the purpose of organic farming, allelopathy can be an important element in balancing the relationship between density and weeds, pests, diseases and cultivars. Relationships among the vegetable species and varieties in particular mixed stand are not sufficiently explored, which is a sufficient reason to conduct such a study. The present study focuses on the allelopathic relationships in agrophytocenoses in order to assess the possibilities of mixed crop cultivation of tomato plants with other vegetable crops and spices. Vegetable species may have a negative, neutral or positive effect one to another when grown in mixed agrophytocenoses. To explore the extent of this impact, test plants from tomatoes have been treated directly with plant extracts from other vegetable plants - parsley, dill, onion and carrots. The study showed that the applied concentrations of parsley, carrot, dill and onion extracts had stimulating, inhibiting or indigenous effect on tomato seed germination, growth and accumulation of dry biomass. Seedling vigor index of plant development (SVIcm) and biomass synthesis (SVIg) depended on the type of the extract applied more than the concentration applied (p<0.05). Seed germination was less affected than root and shoot growth in all species (p<0.05). Length of the seedlings was significantly influenced (positively or negatively) by the allelopathic plants and the effect was stronger with the increment of the extract concentration (p<0.05). Most pronounced negative effect was found at the 1% extract of fresh onion biomass – 34% reduction against the control (p<0.001). Stimulatory effect was strongest at the 1% extract of fresh carrot biomass – 37% increment against the control (p<0.001).