---

A field experiment involving red clover varieties K-39, K-17, Una and Viola was established on an acidic (pH_H2O 4.8) soil to evaluate the effects of foliar application of cobalt (a beneficial nutrient for efficient nitrogen fixation) on seed yield, and on seed yield components. The foliar spray of the crop was carried out using cobalt nitrate [Co(NO₃)₂] with the treatments: one application at the intensive growth phase during the first growth, while two others during the second growth within the second year of cultivation. Seed yield and yield components were recorded from the second growth within the second year of the study. Regardless of foliar cobalt application, the varieties produced a significantly higher seed yield in 2011, when the rainfall received from the onset of flowering until seed maturation was recorded as lower than that in 2010. The foliar treatment with cobalt was in general accompanied by a positive effect on seed yield and seed yield components in all the varieties. As compared with control, a significant increase in seed yield, in the cobalt applied treatment, was obtained only in Viola, mostly due to the significant increase in flower number i.e. seed number per inflorescence. The more favorable response of Viola to foliar cobalt application may have been attributed to a greater percentage of foliage cover during the treatment, as compared with the other varieties. This suggests that foliar cobalt treatment in future studies should be performed at the early stages of development i.e. during intensive growth throughout the first and second cuts, in order to stimulate nodulation and have greater nitrogen fixation in a needed timely manner.

---

An experiment was conducted during eight years (2012–2019) to examine the effect of climatic variations (air temperature and precipitation) on the nutritional quality of berries of three black currant cultivars (‘Ben Lomond’, ‘Titania’ and ‘Čačanska Crna’). HPLC was used for the determination of sugars and organic acids extracted from berries, while ascorbic acid and minerals were evaluated by spectrophotometry. Results indicated that the chemical profile of black currants varied among cultivars. ‘Ben Lomond’ and ‘Čačanska Crna’ exhibited excellent chemical characteristics of the berries, primarily in terms of their high sugars and organic acids content, but ‘Čačanska Crna’ stood out for its highest values of ascorbic acid. Also, seasonal variations caused by temperatures and precipitation affected the biosynthesis of primary metabolites in berries. The heavier precipitation and lower temperatures during berry formation and ripening promoted the accumulation of organic acids and ascorbic acid, as well as minerals P and Fe. Conversely, moderate temperatures and rainfall amounts promoted the synthesis of soluble solids, sugars and proteins, whereas higher temperatures and lower precipitation amount enhanced accumulation of the other tested minerals. PCA analysis showed the correlations among the cultivar/year interactions and identified group patterns. The results showed that the chemical properties of black currant not only depend on the genetic predisposition of the cultivar but also on climatic conditions like air temperature and precipitation, which have an important effect on nutrient metabolism in plants and promote biosynthesis and accumulation of primary metabolites in berries.