Promotion of plant growth and fiber yield in industrial hemp(cannabis sativa L.) plants by soilless culture

Hemp (Cannabis sativa), one of the oldest cultivated plants in human history, is a valuable plant that has economic value in all industrial branches and has superiorities in almost all areas of use. Hemp fibers are among the highest quality fibers and also have antibacterial properties. The use of biotechnological methods in hemp agriculture includes studies to increase the yield and quality of the plant and has become widespread in recent years. Hydroponic method (soilless agriculture), one of the main agricultural biotechnological studies, has an important place in modern agriculture due to its many advantages. In this study, which was carried out in order to include our country in the global industrial product market in a competitive and assertive way with the industrial hemp plant and the products obtained from the fibers of this plant, it was aimed to increase the fiber yield by using soilless agriculture (deep water culture), which is an agricultural biotechnological method. For this purpose, the effects of indole butyric acid (IBA), silicon (Si) and some macro elements (nitrogen, phosphorus, potassium) on plant growth and fiber yield were investigated in Narlı hemp (Cannabis sativa L.), a registered local variety, in deep water culture. Narlı hemp seeds used as starting material were sown in germination medium and left to grow for 2 weeks. At the end of 2 weeks, hemp plants that produced the 2nd pair of true leaves were grown in 3 different deep water culture media (Group-1: N:P:K nutrients at a ratio of 255:45:267; Group-2: NPK + 10 ppm Si; Group-3: NPK + 1 ppm IBA) and soil pot (Group-4: soil:peat:perlite / 1:1:1) for approximately 2 months. At the end of this period, the effects of different growing media and different treatments in growing media were investigated in the light of root fresh-dry weight, stem fresh-dry weight, stem length, stem thickness, leaf length and width, relative water content (%RWC), photosynthetic pigment content, malondialdehyde (MDA), leaf secondary metabolite (CBD, THC, CBN) content, % fiber content, total cellulose content parameters in the harvested plants. Pooling method was used in the harvested plants to ensure 100% separation of fibers from the woody part of the plant. As a result of the analysis, it was determined that the soilless medium gave better results than the soily medium in terms of root fresh--dry weight, stem fresh--dry weight, stem length, stem thickness, leaf length and width, %RWC, photosynthetic pigment content, % fiber content, total cellulose content. However, the lowest results were obtained in the soilless medium in terms of MDA content and leaf secondary metabolite (CBD, THC, CBN) content, which are indicators of stress in the plant. In all these parameters, it was determined that hemp plants grown in deep water culture medium containing Si gave the best results among the groups tested. In the study, it was observed that IBA treatment in deep water culture gave the lowest results in all developmental parameters of the plant in general. IBA-treated plants had the lowest values in terms of fiber yield, cellulose content, plant height, stem/root fresh-dry weight, %RWC, while had the highest values in terms of MDA and secondary metabolite (CBD, THC, CBN) content, which increased under stress. When the results related to increasing fiber yield, which is one of the main objectives of this thesis study, were evaluated; fiber content was 29.122% in Group-2; 24.018% in Group-1; 19.989% in Group-4; 13.743% in Group-3. The cellulose content, which is the determinant of fiber quality, was determined to be in the range of 61% to 82% on average in the tested treatments. The highest total cellulose content of 82% was obtained from plants grown in Si-treated deep water culture medium. As a result, better results were obtained in terms of both fiber yield and fiber quality in hemp plants grown by Si-treatment in deep water culture compared to soil environment. Considering these results, a significant alternative that can be applied in the cultivation of industrial hemp plants has been presented with the deep water culture method used. Since this thesis study is the first research in this field in our country, it is thought that it will contribute significantly to the gap in the literature regarding the increase of fiber yield in hemp plants through agricultural biotechnological methods.