Introduction: Global climate change-induced abiotic stresses such as drought have profound impacts on crop yield and the subsistence farming economy in Iran. Biostimulants are an effective type of substances obtained from some organic and inorganic materials and from microorganisms. These materials, as a promising and eco-friendly approach, are widely used to decrease the destructive effects of drought stress and fulfill the need for developing sustainable/modern agriculture. Current knowledge revealed that biostimulants derived from plants and animals (e.g., seaweeds and phytoextracts, humic substances, amino acids and fulvic acid) as well as microbial stimulants such as plant growth promoting bacteria (PGPR) have high potential to elicit plant tolerance to drought stress. Fertilizer materials directly supply plants with essential nutrients, correcting nutrient deficiencies in plants and promoting plant growth. In contrast, growth biostimulants promote the plant's innate abilities to absorb nutrients from soil and alleviate stresses, without providing nutrients directly. The aim of this study was to investigate the effect of biostimulants on wheat tolerance under deficit water condition.
Materials and Methods: Experiments conducted in form of split plots as a complete randomized block design with three replications in Ilam for two years since 2021. The soil order The main plots include two levels as irrigation application after 70 and 140 mm cumulative evaporation and sub-plots including six levels of biostimulants as control, foliar application of amino acid, fulvic acid and seaweed, fertigation of humic acid, azotobacter inoculation and combined application of all biostimulants. At the end, after harvesting wheat, grain and biological yield and the concentration of nitrogen, phosphorus, potassium, iron, zinc, copper and manganese elements in grain and straw were measured. Analysis of data and mean comparison was performed with SAS software and Tukey^, s test, respectively.
Results and Discussion: The results showed that the application of biostimulants under deficit irrigation improved the yield, relatively. The combined biostimulants application with 12.9% increase in grain yield was the superior treatment. Under normal conditions, the use of amino acids and under conditions of deficit irrigation, the application of fulvic acid produced 10.3% and 12.8% increase in grain yield, respectively. The increase in nutrient concentration with the application of biostimulants was between 11% and 18%. . The highest concentration of phosphorus in the grain was obtained with the combined application of growth stimulants, the sole application of fulvic acid and the sole application of amino acid with concentrations of 0.227, 0.225 and 0.223%, respectively. Also, the highest concentration of potassium in straw was obtained with the combined application of growth stimulants with a concentration of 0.136%. The highest concentration of potassium in the grain was obtained with the combined application of growth stimulants and the sole application of fulvic acid with concentrations of 0.633 and 0.593%, respectively. Among the biostimulants, the best results under deficit irrigation and normal conditions were obtained by fulvic acid and amino acid, respectively. In general, biostimulants, due to the presence of plant growth-promoting compounds such as nutrient elements, phytohormones and enzymes, can improve plant growth characteristics and nutrient absorption. Also, these materials improved growth parameters due to its role in increasing photosynthesis respiration, cell membrane permeability and root architecture.
Conclusion: In general, the application of growth stimulants compared to the control treatment improved the yield components and changed the concentration of nutrients in wheat grain and straw. In the condition of dehydration, the absorption of nutrients decreased and the consumption of growth stimulants could have a positive effect on the process of absorption of nutrients and reduce the negative effects of dehydration. Fulvic acid was more effective than other biostimulants in decreasing the negative effects of drought stress. Finally, the use of natural materials such as fulvic acid can be a safe approach and complementary additive to improve plant growth and to decrease the adverse effects of not only drought stress but also chemical fertilizers.






Extended Abstract

Introduction

Global climate change-induced abiotic stresses such as drought have profound impacts on crop yield and the subsistence farming economy in Iran. Biostimulants are an effective type of substances obtained from some organic and inorganic materials and from microorganisms. These materials, as a promising and eco-friendly approach, are widely used to decrease the destructive effects of drought stress and fulfill the need for developing sustainable/modern agriculture. Current knowledge revealed that biostimulants derived from plants and animals (e.g., seaweeds and phytoextracts, humic substances, amino acids and fulvic acid) as well as microbial stimulants such as plant growth promoting bacteria (PGPR) have high potential to elicit plant tolerance to drought stress. Fertilizer materials directly supply plants with essential nutrients, correcting nutrient deficiencies in plants and promoting plant growth. In contrast, growth biostimulants promote the plant's innate abilities to absorb nutrients from soil and alleviate stresses, without providing nutrients directly. The aim of this study was to investigate the effect of biostimulants on wheat tolerance under deficit water condition.

Methods and material

Experiments conducted in form of split plots as a complete randomized block design with three replications in Ilam for two years since 2021. The soil order The main plots include two levels as irrigation application after 70 and 140 mm cumulative evaporation and sub-plots including six levels of biostimulants as control, foliar application of amino acid, fulvic acid and seaweed, fertigation of humic acid, azotobacter inoculation and combined application of all biostimulants. At the end, after harvesting wheat, grain and biological yield and the concentration of nitrogen, phosphorus, potassium, iron, zinc, copper and manganese elements in grain and straw were measured. Analysis of data and mean comparison was performed with SAS software and Tukey, s test, respectively.

Results and Discussion

The results showed that the application of biostimulants under deficit irrigation improved the yield, relatively. The combined biostimulants application with 12.9% increase in grain yield was the superior treatment. Under normal conditions, the use of amino acids and under conditions of deficit irrigation, the application of fulvic acid produced 10.3% and 12.8% increase in grain yield, respectively. The increase in nutrient concentration with the application of biostimulants was between 11% and 18%. . The highest concentration of phosphorus in the grain was obtained with the combined application of growth stimulants, the sole application of fulvic acid and the sole application of amino acid with concentrations of 0.227, 0.225 and 0.223%, respectively. Also, the highest concentration of potassium in straw was obtained with the combined application of growth stimulants with a concentration of 0.136%. The highest concentration of potassium in the grain was obtained with the combined application of growth stimulants and the sole application of fulvic acid with concentrations of 0.633 and 0.593%, respectively. Among the biostimulants, the best results under deficit irrigation and normal conditions were obtained by fulvic acid and amino acid, respectively. In general, biostimulants, due to the presence of plant growth-promoting compounds such as nutrient elements, phytohormones and enzymes, can improve plant growth characteristics and nutrient absorption. Also, these materials improved growth parameters due to its role in increasing photosynthesis respiration, cell membrane permeability and root architecture.

Conclusion

In general, the application of growth stimulants compared to the control treatment improved the yield components and changed the concentration of nutrients in wheat grain and straw. In the condition of dehydration, the absorption of nutrients decreased and the consumption of growth stimulants could have a positive effect on the process of absorption of nutrients and reduce the negative effects of dehydration. Fulvic acid was more effective than other biostimulants in decreasing the negative effects of drought stress. Finally, the use of natural materials such as fulvic acid can be a safe approach and complementary additive to improve plant growth and to decrease the adverse effects of not only drought stress but also chemical fertilizers.



Key words: Amino acid, Azotobacter, Fulvic acid, Humic acid, Seaweed extract