Preparation of new chelated iron compounds and their use in foliar plant nutrition applications

In agricultural micro-nutrient fertilizer applications, it has been observed that unwanted occurrences such as the solubility problem of metal salts in the natural soil environment affect the uptake of metals by plants. The deficiency of micro-nutrient elements leads to a decrease in total chlorophyll and total carotenoid levels, negatively impacting plant growth and development. To address these issues, commercial metal complexes that can overcome solubility problems and balance the uptake of metals by plants have been used. While there have been findings in the literature about the application of chelators like EDDHA (Ethylenediamine-N,N'-bis(2-hydroxyphenylacetic acid)) and HBED (N,N'-bis(2-hydroxybenzyl)ethylenediamine-N,N'-diacetic acid) to achieve more efficient results with less micro-nutrient elements and prevent environmental pollution, there have been no applications of iron complexes synthesized from alternative new ligands. Furthermore, previous studies have shown that chelated fertilizers used in foliar applications increase metal mobility despite a decrease in metal uptake from the leaves compared to inorganic salt forms, leading to increased efficiency. Based on the literature data, the aim of this thesis was to determine the fertilizer potentials of the iron complexes whose synthesis and characterization were completed within the scope of this study. In the conducted research within the scope of this thesis, new chelating iron complexes were synthesized that can prevent the conversion of iron from micro-nutrient elements into unusable or less usable forms for plants and can create a synergistic effect with Tween 20. The structural analyses of synthesized N'1,N'4-bis(2-hydroxybenzoyl)fumarohydrazide (DSHM) and N,N''-bis(2-hydroxybenzoyl)methanedihydrazide (KDHDS) ligands and their iron complexes were carried out using well-known spectroscopic methods (FTIR, 1H-NMR, 13C-NMR, MASS, UV-Vis, Elemental Analysis) to elucidate their molecular structures. The originally qualified iron complexes with completed structural analysis were then formulated for root and foliar applications. For root applications, the amount of iron in the Hoagland nutrient solution (Appendix B, Table B1) was determined, and by displacing EDTA-Fe with DSHM-Fe and KDHDS-Fe to have the same amount of iron as the control group, the formulations were prepared and made ready for application. For foliar applications, two different application solutions were prepared, one containing the same amount of iron as the nutrient solution and the other containing 0.1% Tween-20 (Polyoxyethylene sorbitan monolaurate) used as an agricultural adjuvant. Additionally, the plants were continuously grown in iron-free Hoagland nutrient solution in hydroponic conditions for foliar applications. Both root and foliar application groups were divided into control groups, with one group grown in iron-free Hoagland solution (Fe-free) and the other in Hoagland nutrient solution with a known iron content. All cucumber (Cucumis sativus) seeds of the Beith Alpha genotype were placed in glass petri dishes and left to germinate in darkness for 7 days. at 25°C and 40% relative humidity in a climatic chamber. Germinated cucumber seeds were then grown in hydroponic conditions in Hoagland nutrient solution without iron (Fe-free) under controlled conditions [(16 hours light / 8 hours dark photoperiod, light intensity (150 μmol m-2 s-1 temperature (25/20°C), and relative humidity (40%)]. The plants were grown for 28 days in these conditions. At the end of 28 days, cucumber plants grown in iron-free Hoagland solution were divided into groups for root and foliar applications and compared with the application of DSHM-Fe and KDHDS-Fe complexes synthesized within the scope of the thesis, commercial iron fertilizer Tariron, and Sequesterene in hydroponic conditions. Additionally, the foliar application groups were further divided into two groups, one with Tween 20 and the other without Tween 20, to apply different plant nutrition formulations. All control and experimental cucumber plants were grown separately in nutrient solutions with known iron content. Furthermore, the iron-free control group plants and foliar application group cucumber plants were grown in hydroponic conditions with iron-free Hoagland solution, and the foliar application was repeated five times at three-day intervals. After the application, cucumber plants were harvested, and physical parameters such as root length, shoot length, stem thickness, and true water content were analyzed. Moreover, leaf samples from the plant groups were taken to measure the changes in total chlorophyll, total carotenoid, and malondialdehyde (lipid peroxidation: MDA) levels using appropriate methods. The measurement results obtained from control and commercial fertilizers were statistically evaluated and compared. According to the results of the foliar and root application studies conducted, it was determined that the most effective groups were Commercial Tariron, Hoagland, and DSHM-Fe with 0.1% Tween 20. Furthermore, among the foliar application groups, it was observed that the best results were obtained from the groups with Tween 20 application, both Tween 20-treated and untreated groups being separated within themselves. This indicates that applying chelated-Fe foliarly with 0.1% Tween 20 in the formulation increases foliar penetration, which is in line with the literature data. On the other hand, the changes in the biological parameters obtained from cucumber fresh leaves from foliar applications were found to be in agreement with the physical parameters for commercial fertilizers, Hoagland, and DSHM-Fe with 0.1 % Tween 20. However, contrary to expectations, the amount of MDA (lipid peroxidation) in these groups was found to be quite high. Comparing the MDA results with the literature data, it was determined that the increasing amount of malondialdehyde is one of the stress parameters of the plant, and as MDA levels increase, the amount of cell damage also increases. In root feeding studies, the analysis results of both physical and biological parameters revealed that the most effective results were obtained from Tariron, Sequesterene, Hoagland, and DSHM-Fe groups. However, in the results obtained for the changes in the amount of MDA in the biological parameters, the highest change was observed in Tariron and KDHDS-Fe groups, while the lowest change was observed in the DSHM-Fe group. In addition to these studies, all nutrient solutions used in both foliar and root applications were prepared based on the iron concentration in the Hoagland nutrient solution, except for the iron-free (Fe-free) control group, and applied separately to each cucumber plant group. At the end of the application, cucumber leaf samples were dried, and the amount of iron per 0.1 g of plant (ppm) was calculated. For the cucumber plant groups from root applications, it was determined that the most iron uptake was supported by the commercial Tariron iron fertilizer and statistically by the DSHM-Fe compound. Among the cucumber plant groups subjected to root application, it was observed that the highest plant iron uptake was supported by the commercial Tariron iron fertilizer and statistically by the DSHM-Fe compound, and the analysis results of total chlorophyll and total carotenoid were evaluated comparatively, showing a consistency with the ICP-OES results in determining the plant iron content. In the cucumber groups subjected to foliar plant feeding, when the iron uptake was compared based on the ICP-OES results, it was found that the best results were obtained from the Tariron + Tween 20 and Tariron iron fertilizer formulations among the results obtained from commercial fertilizer applications. Among the groups other than the commercial fertilizers, the analysis results of total chlorophyll and total carotenoid for the synthesized DSHM-Fe compound were evaluated comparatively, and it was found that the plant iron uptake was consistent. As a result, it has been demonstrated that the data related to the DSHM-Fe complex synthesized within the scope of this thesis positively influenced the plant growth and development parameters and showed fertilizer potential in root applications.