The Effect of Different levels of Damask Rose Waste (DRW), Walnut Green Skin Waste (WGW) and Cow Manure Biochars on Biochemical, Physiological and functional Characteristics of European Borage (Borago officinalis L.)

Introduction Borage (Borago officinalis L.) is a valuable annual medicinal herb suitable for cultivation in many countries, including Iran. Borage is considered as a native of both Europe and Asia. Several species around the world fall under the denomination of “borage”. The presence of the γ-linolenic acid in the seeds of borage makes borage distinctively important mainly for the nutraceutical and pharmaceutical research. γ-Linolenic acid is an omega -6 polyunsaturated fatty acid which cannot be synthesized in the body and hence falls into the category of essential fatty acids (Evesh et al., 2019).  Chemical fertilizer is an indispensable abiotic factor in agricultural production, especially nitrogen fertilizer. However, in order to improve the yield, people fertilize a lot, which not only wastes resources, but also brings a series of serious problems to the environment, such as greenhouse gas emissions, soil fertility degradation and water resources pollution. Therefore, developing new fertilizers, improving crop nutrient utilization efficiency, replacing chemical fertilizers and reducing environmental pollution is an important direction of agricultural sustainable developme (Zhang et al ., 2020). Biochar is a carbon rich product formed by pyrolysis of agricultural and forestry wastes under limited air availability. It is generally alkaline in nature, with the characteristics of rich carbon content, large specific surface area and strong adsorption. Biochar addition can reduce soil bulk density and increase porosity, pH, water holding capacity and nutrient content. Additionally, the unique physical properties of biochar can also promote the colonization and growth of some specific microorganisms, which may participate in the mineralization of biochar and promote nutrient cycling. Therefore, biochar has been widely used on improving soil quality and increasing crop productivity. Biochar has a positive effect on root structure and nutrient absorption of plant. Several studies have shown biochar can significantly increase the root length, root biomass, root surface area and specific root length. The study also found that biochar significantly increased the number of plant root tips, the most active part of root, and then increased the ability of plants to absorb nutrients from soil (Zhang et al, 2020).   Materials and Methods In order to evaluate the effect of damask rose waste (DRW), walnut green skin waste (WGW) and cow manure biochars on biochemical, physiological and yield characteristics of European borage, an experiment was carried out based on a completely randomized design at the greenhouse conditions in Faculty of Agriculture, Shahid Bahonar University of Kerman. The experimental treatments contain: without of biochar (control), biochars of cow manure (0.75%, 1.25%, 2.5% and 5% w/w), walnut green skin biochar (WGW) (0.75%, 1.25%, 2.5% and 5% w/w) and damask rose waste biochar (DRW) (0.75, 1.25, 2.5 and 5% w/w). The physicochemical properties of the biochars and soil were analyzed. Five seeds were planted in three-kilogram pots at a depth of 1.5 to 2 cm. The greenhouse was maintained at an average temperature of 25 °C during the day and 20 °C at night, with a relative humidity level of 60%. Upon concluding the experiment, various biochemical, physiological, and functional characteristics of European borage were assessed and measured.   Results and Discussion The results showed that DRW (60%) and WGW (13%) biochars had the highest and lowest amount of stable organic carbon, respectively. The investigated treatments significantly (p≤ 0.01) affected the biochemical, physiological and performance traits of European borage. Application of DRW and manure biochars caused a significant (p ≤ 0.01) increase in yield and photosynthetic pigments of European borage compared to the control. Applying WGW biochar at the level of 2.5% increased the shoot dry weight of the plant by 119% compared to the control treatment. Application of 1.25% of cow manure biochar also increased the shoot dry weight by 29.7%. WGW biochar applying not only had no positive effect on the growth and yield of the European borage, but also lead the decreasing growth and prevent flower production of borage. The highest CAT activity related to applying 2.5% of DRW biochar and 1.25% of manure biochar. Application of WGW in concentration of 0.75% significantly increased the proline contents. Using biochar improves soil fertility.   Conclusion In general, applying DRW biochar in concentration of 2.5% and cow manure biochar in concentration of 1.25% were the most suitable treatments.