Unraveling Zinc Toxicity Thresholds in Soil and Leaves of Field-grown Soybean and Their Impacts on the Antioxidant Defense System, Nutritional Status, and Physiological Performance
This field study on soybean grown in tropical clayey Oxisols establishes critical zinc toxicity thresholds of 13 mg dm⁻³ in soil and 76 mg kg⁻¹ in leaves, demonstrating that excessive zinc reduces grain yield and photosynthetic efficiency primarily through oxidative stress and insufficient antioxidant defense rather than nutritional imbalances.