Investigation of Biochar Application Effect on Photosynthetic Pigments, Enzymes Activity and Yield of Safflower (Carthamus tinctorius L.) under Water Stress

Introduction Water stress is one of the main factors in crop growth in arid and semi-arid regions of the world, which limits the grain yield of the safflower (Carthamus tinctorius L.). To increase the soil fertility and yield of crops, it is necessary to pay sufficient attention to the use of biomass of organic matter, especially crop residues, and its conversion to biochar. This research aims to evaluate the biochar application produced from cotton and wheat residues under late-season water stress in the south of Fars province (Darab) on photosynthetic pigments, enzyme activity, yield components, and yield of safflower. Materials and Methods In order to investigate the biochar application and water stress on the amount of photosynthetic pigments, enzyme activity, and yield of safflower, a field experiment was laid out as split plots in the form of randomized complete block design with 3 replications in the 2019-2020 growing season. The experimental factors include the irrigation regime as the main factor in two levels (optimal irrigation and cutting off irrigation after the flowering stage), and the secondary factors were fertilizer treatment as subplot including control (without fertilizer), consumption of 3 tons of biochar from wheat residues per hectare, consumption of 3 tons of biochar from cotton residues per hectare, consumption of 150 kg of urea per hectare + 50 kg of triple superphosphate per hectare, consumption of 112.5 kg of urea per hectare + 37.5 kg of triple superphosphate per hectare, consumption of 112.5 kg of urea + 37.5 kg of triple superphosphate + 3 tons wheat biomass per hectare, and 112.5 kg of urea + 37.5 kg of triple superphosphate + 3 tons of cotton biomass per hectare. In this research, chlorophyll a and b, total chlorophyll, catalase, and peroxidase activities, yield components, and yield of safflower were calculated. Results and Discussion The results of the experiment showed that the measured traits were significantly affected by the irrigation regime and fertilizer treatment. Under cutting-off irrigation after the flowering stage, the fertilizer treatment of 112.5 urea + 37.5 phosphate + 3 tons of wheat biochar per hectare increased 55 and 40% chlorophyll a and total chlorophyll compared to the control, respectively. Water stress increased the carotenoid content, catalase, and peroxidase enzymes. The highest amount of catalase and peroxidase enzyme activity was obtained in the control under cutting-off irrigation after the flowering stage, which increased by 48 and 38%, respectively, compared to the control under optimal irrigation. The number of seeds per capitule and the number of fertile capitules per plant in the treatment of 112.5 urea + 37.5 phosphate + 3 tons of cotton biochar under water stress conditions increased by 8.8 and 19.51%, respectively. Also, under water stress, the application of 112.5 urea + 37.5 phosphates + 3 tons of cotton biochar improved and increased the relative content of leaf water, biological capitules yield, and grain yield compared to the control by %53, %22, and %34, compared to control, respectively. Conclusion Results showed that in both of the irrigation regimes, application of 3 tons of cotton or wheat biochar alone can increase the biomass and grain yield compared to control. Overall, the application of 112.5 urea + 37.5 phosphate + 3 tons of cotton biochar under water stress conditions improved the relative water content of the leaves, the number of seeds per capitule, the number of fertile capitule per plant, and finally, biomass and yield of safflower. With respect to water shortage under late season in southern parts of Fars province, and in order to decrease the detrimental effects of water stress, farmers can use the biochar of cotton combined with reduced dosage of urea and triple superphosphate fertilizers.