Effect of drought stress and biofertilizer on yield and physiological characteristics of cotton (Gossypium hirsutum L.) in Isfahan climatic

Background and objectives: Drought stress is one of the most important factors that reduce the yield of crops in arid and semi-arid regions, including the climatic conditions of Iran. In the conditions of drought stress, one of the solutions to reduce the negative effects caused by drought stress and as a result increase water absorption is the development of roots through the use of biological fertilizers. Therefore, the present study was conducted to investigate the effect of drought stress and the application of nitrogen and phosphorus biofertilizers on the yield and some physiological characteristics as well as the content of photosynthetic pigments of cotton.
Materials and methods: The experiment was conducted as a split plot with a randomized complete block design in three replications. In this research, irrigation levels include normal irrigation during the growth period as a control (60 mm evaporation from the evaporation pan), medium drought stress during the growth period (90 mm evaporation from the evaporation pan) and severe drought stress during the period. growth (120 mm of evaporation from the evaporation pan) as the main factor and 4 biofertilizer treatments, including no use of biofertilizer (control), Aztobacter biofertilizer, biophosphorus biofertilizer, and the combination of Aztobacter biofertilizers and biophosphorus as secondary factors.
Results: The results showed that the yield, physiological characteristics and content of photosynthetic pigments were affected by the experimental treatments. Drought stress led to a decrease in plant height, yield, chlorophyll a, chlorophyll b, total chlorophyll and carotenoid. Drought stress increased the content of soluble sugars and proline, and although it reduced the relative content of leaf water and cell membrane stability, the application of biofertilizers improved them. The highest proline content of 3.63 mg/g fresh weight of leaves was obtained in the treatment of simultaneous application of biofertilizers Aztobacter and biophosphorus and at the level of drought stress treatment. The highest total chlorophyll content was obtained in the control treatment and the combined use of biophosphorus and azotobacter fertilizers at the rate of 3.75 mg/kg. The results showed the negative effect of drought stress on rice yield, so that in the control treatment, rice yield was 3536 kg per hectare, while in medium and severe drought stress treatments, rice yield was 2550 and 1495 kg per hectare, respectively. Also, the simultaneous application of biophosphorus and azotobacter fertilizers with their synergistic effect led to a further increase in rice yield up to 2722 kg/ha.
Conclusion: In general, the results showed that drought stress led to a decrease in cotton photosynthetic pigments, relative