The Effect of Foliar Zinc Application on the Leaf Chlorophyll Concentrations and Grain Yields of the Winter Wheat (Triticum aestivum L.) in the Field Experiments of Two Seasons

This research examined the effectiveness of zinc foliar fertilizers. Two winter wheat varieties, GK Pilis and Zvezdana, were tested in a Zn-limited meadow chernozem soil. Crop yields and chlorophyll concentrations of the leaves were examined in the growing seasons of 2020/2021 of favorable weather conditions and 2021/2022 of drought weather conditions. In the experiment, three treatments were carried out with monozinc foliar fertilizer of a concentrated 12% (w/v) zinc sulfate heptahydrate solution, and the fourth plot was designed as the untreated control. The first monozinc treatment was applied at a dose of 1 L ha(-1) and the second monozinc treatment at a dose of 2 L ha(-1). These treatments were applied at tillering (BBCH 21-22). The third monozinc treatment was applied at a dose of 1 L ha(-1) at tillering and flag leaf emergence (BBCH 21-22, BBCH 37). Samples were taken several times in the vegetation period, and measurements were made using different methods (SPAD, determination of total chlorophyll concentration from acetone solution) before and after Zn treatments. In 2020/2021 of favorable weather conditions, the yield of Zvezdana was 5.47 t ha(-1) and that of Gk Pilis was 6.11 t ha(-1), compared to 2021/2022 of drought weather conditions, in which year the yield of Zvezdana was 3.14 t ha(-1) and that of Gk Pilis was 2.79 t ha(-1). Yields of both varieties increased with increasing NPK nutrient doses. In 2021/2022, even at nutrient level D (NPK basal fertilizer and two-times N topdressing), we harvested on average twice as much as in 2020/2021 at nutrient level A (N basal fertilizer and once N topdressing). No significant effects were found between the foliar fertilizers in 2020/2021. In 2021/2022, Zn treatments, mainly at four nutrient levels tended to increase the yields of both varieties. The first treatment resulted in a grain yield reduction of 3% for GK Pilis, and the second treatment resulted in a grain yield reduction of 1.2% for Zvezdana. After the second and third treatments, grain yield reductions were 0.1%-0.5%. Although there was no significant difference in terms of the main averages, foliar fertilizer was found to be effective in the second year. The relationship between chlorophyll and grain yield was found to depend on the year and variety. A weak correlation (r = 0.33, p < 0.05) was found between the total chlorophyll concentration in leaves for Zvezdana in 2021, and a medium correlation for GK Pilis (r = 0.67, p < 0.05). Concerning grain yield and chlorophyll concentration, a strong correlation (r = 0.81, p < 0.05) was found for Zvezdana in 2022, and a weak correlation (r = 0.44, p < 0.05) for GK Pilis. A strong correlation was found between the total leaf chlorophyll concentration and SPAD index in both years (r = 0.81, p < 0.05)