Influence of Physiologically Active Substances on the Mineral Composition of Sweet Cherry (Prunus avium L.) Leaves

The cultivation of sweet cherry takes place in various climatic zones, where the plant may be exposed to different types of environmental stress during the growing season, which can significantly affect yield and fruit quality. The role of various physiologically active compounds is crucial for plant resistance to stressful environmental conditions. The aim of this study is to determine how the foliar application of different physiologically active substances affects the mineral composition of sweet cherry leaves. Research was performed in 2022 and 2023 at two locations (Ninski Stanovi and Murvica) in Zadar County with the Regina variety. The trials included five foliar treatments (T0—water only, T1—Ca nutritional supplement, T2—biostimulant (Ascophyllum nodosum L.), T3—proline solution, T4—salicylic acid solution). Leaf samples were collected for the analysis of the following macro-elements: total carbon (TC), total nitrogen (TN), calcium (Ca), magnesium (Mg), potassium (K), and phosphorus (P). On average, significantly higher TN content in leaves was found only in T2 (15% higher than T0). Ca, Mg, and K contents in leaf dry matter in all variants were higher by 20–29%, 13–20%, and 12–14%, respectively, compared to the control variant. The significant correlations were found between Ca and Mg, Ca and P, as well as Ca and K contents. This study shows a significant impact of the applied compounds on sweet cherry leaf mineral composition, and considering the year and locality effects, further testing of these treatments in different environments could be suggested.