OICC Press Journal of Crop Nutrition Science 2538-2470 11 2 2026 06 13 Response of Physiological and Biochemical Characteristics of Red Bean (Phaseolus vulgaris L.) to Chemical and Biological Nitrogen Fertilizers at Different Densities in South West of Iran (Lorestan Province) 10.57647/jcns.2025.1102.12 EN Mamak Khorramabadi Department of Agronomy, Bo, C., Islamic Azad University, Borujerd, Iran. Amin Farnia Department of Agronomy, Bo, C., Islamic Azad University, Borujerd, Iran. Shahram Nakhjavan Department of Agronomy, Bo, C., Islamic Azad University, Borujerd, Iran. Journal Article 2026 06 13 BACKGROUND: Inappropriate crop density and weak soil fertility are two main factors affecting on physiological and biochemical characteristics of red bean. Application of chemical and biological Nitrogen fertilizer may promote some physiological traits such as leaves pigments, protein, sugar, relative water content (RWC) and also enzymatic antioxidant system. OBJECTIVES: This study was laid out in order to investigate the effect of chemical and biological Nitrogen fertilizers on some physiological traits and antioxidant system of Red Bean at different densities. METHODS: The experiment was conducted via split-split plot based on randomized complete block design with four replications. Plant density treatments (30, 40 and 50 plants.m-2) belonged to main plots, Nitrogen fertilizer (120 and 144 kg.ha-1) in the sub-plots, and biofertilizer treatments (control, Rhizobium, Nitroxin and Rhizobium + Nitroxin) were for sub-sub-plots. RESULT: The results showed that grain protein affected by plant density and Nitrogen nutrition, so that maximum grain protein was related to both application of chemical Nitrogen and Nitroxin + Rhizobium fertilizers at 50 plants.m-2 density in Azna (25.56%) and Dorud (25.23%) regions. Increase of plant density led to decrease of relative water content (RWC) from 83% until 54%. Also, the highest grain carbohydrates (186.75 mg.g-1), chlorophyll a (2.67 mg.g-1), chlorophyll b (1.25 mg.g-1) and total chlorophyll (3.92 mg.g-1) were related to 30 plant.m-2 density and both application of chemical Nitrogen fertilizer and Nitroxin. Based on the results, both applications of Nitroxin and Rhizobium, along with chemical Nitrogen fertilizer led to higher leaf Carotenoid at 30 plant.m-2 density by 1.7 mg.g-1. Enzymatic antioxidant system was affected by plant density and fertilizers. Results revealed that maximum Catalase (CAT) activity (2798 nmol.min-1.g-1) was obtained in chemical Nitrogen fertilizer treatment at 50 plant.m-2 density. The simultaneous application Nitroxin and Rhizobium along with chemical Nitrogen fertilizer produce the highest level of Peroxidase (POX) (305.5 nmol.min-1.g-1), Superoxide dismutase (SOD) (1.21 micromol.min-1.g-1) and Glutathione reductase (GR) (945 micromol.min-1.g-1) activities at 30, 40 and 50 plant.m-2 densities. CONCLUSION: Application of Nitroxin and Rhizobium result to higher antioxidant enzymes activity such as CAT, POX, SOD and GR, which promote ROS saved cells from oxidation damages. However, better physiological and biochemical status in red bean achieved with application of biological and chemical Nitrogen fertilizers at 30 plant.m-2 density. Also, the best treatment for achieving of higher plant pigments and antioxidant enzymes activity was application of Nitroxin and chemical Nitrogen fertilizer at 30 plant.m-2 density and application of Nitroxin + Rhizobium and chemical Nitrogen fertilizer at 40 plant.m-2 density respectively.