The study is conducted at the experimental base of Department of Plant productionat Trakia University, Stara Zagora. Triticale is grown after five predecessors anddifferent nitrogen fertilization rates. The predecessors are wintering peas, springpeas, sunflower, common wheat and triticale. Nitrogen fertilization rates are 0 (N0),40 (N40), 80 (N80), 120 (N120) kg ha-1 after legumes and 0 (N0), 60 (N60), 120 (N120),180 (N180) kg ha-1 after the other predecessors. The influence of the predecessorsand nitrogen fertilization on the nitrogen uptake, assimilated nitrogen fromfertilization, nitrogen utilization and nitrogen required for 100 kg produce oftriticale is established. Nitrogen assimilation from fertilization increases with theincrease of the nitrogen fertilizer rates. With the obtained yield from triticale anaverage of 96.53 kg ha-1 N is extracted from the soil with the grain, 18.97 kg ha-1 Nwith the straw or a total of 115.50 kg ha-1 N. When growing triticale afterleguminous predecessors the utilization of nitrogen is 35.39% and afterpredecessors sunflower, wheat and triticale - 28.76%. Nitrogen required for 100 kgyield of grain of triticale is 1.9 kg of nitrogen when growing after legumepredecessors and 2.8 kg of nitrogen after the other predecessors.

Stevia rebaudiana Bertoni is a plant species which is frequently used not only as a sweetener, but also for its antibacterial and antioxidant properties. Nowadays, there are a large number of studies on the antimicrobial and antioxidant activity of S. rebaudiana leaves, but there are almost no data about the antimicrobial and antioxidant potential of extracts from the other parts of S. rebaudiana. The aim of the present study is to provide data of the antibacterial and antioxidant potential of methanolic extracts from different parts of S. rebaudiana (flowers, leaves, stems, rhizomes, and tubers) cultivated in Bulgaria. Antibacterial activity of the extracts against Staphylococcus aureus, Bacillus cereus and Escherichia coli was evaluated by agar well diffusion method, rutin content - by HPLC method, total phenolic content and radical scavenging potential - by UV-Vis analysis. S. rebaudiana extracts demonstrated antibacterial activity mainly against S. aureus - flower extracts expressed the highest activity, followed by the leaf and stem extracts. Only flower and leaf extracts demonstrated very low antibacterial activity against B. cereus. S. rebaudiana extracts did not show any antibacterial activity against E. coli. Methanolic extracts of this plant are rich in antioxidants. The highest concentrations of rutin and total phenols were found in the rhizomes of the plants, followed by the leaves, tubers, flowers, and stems, which corresponded to the radical scavenging potential of the same plant part. Comparisons between Trolox equivalents and gallic acid equivalents in different parts of S. rebaudiana on one hand, and Trolox equivalents and rutin concentration on the other hand showed a positive dependence and high values of the Pearson correlation - 0.9612 and 0.9707, respectively. The most important part of S. rebaudiana with medicinal significance (the leaves) has both comparatively good antibacterial activity and high antioxidant content, although the flowers and rhizomes expressed higher antibacterial and antioxidant activity, respectively. The experimental results imply that the cultivation area and climatic conditions of Bulgaria are very suitable for cultivation of S. rebaudiana plants with high content of antioxidants.

The aim of this study was to determine the effect of organic leaf fertilization on the chemical composition, nutritive value, yield of crude protein (CP) and feed units of natural Agropyron repens grassland in the region of South-Central Bulgaria (305 m altitude). The experiment was carried out with leaf organic fertilizer Naturamin Plus, during the period 2018-2019. The trial was designed by the block method in 4 repetitions and 3 doses of fertilizer were tested: 1500; 2500 and 3500 ml/ha. The obtained results were statistically processed by ANOVA. The applied leaf organic fertilizer Naturamin Plus promoted a positive effect on the productive parameters of natural Agropyron repens grassland but had no significant effect on the chemical composition and nutritive value of the harvested biomass. The results demonstrated that yield of CP, feed units for milk (FUM) and feed units for growth (FUG) increased significantly by fertilization with a dose of 2500 ml/ha -respectively 22.2%, 29.7% and 29.4% more compared to the control.

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