Nano zinc-enriched biochar improves spinach growth and soil nutrient dynamics in degraded soils

Soil degradation threatens food security by reducing fertility and crop productivity, requiring innovative solutions to enhance crop growth in compromised soils. This study investigates the efficacy of nano zinc-enriched biochar in improving spinach growth under degraded soil conditions. The biochar, derived from locally available biomass, exhibited high porosity, a stable carbon structure, and essential plant nutrients. The degraded soil, collected from intensively cultivated fields, had a silt loam texture, low organic matter (0.21%), slightly alkaline pH (7.63), and a zinc concentration of 0.41 mg kg⁻¹. A greenhouse pot experiment was conducted using a randomized complete block design to evaluate six treatments: T1 (control), T2 (ZnO 6 mg kg⁻¹), T3 (biochar 8 g kg⁻¹), T4 (biochar 4 g kg⁻¹ + nano ZnO 2 mg kg⁻¹), T5 (biochar 6 g kg⁻¹ + nano ZnO 4 mg kg⁻¹), and T6 (biochar 8 g kg⁻¹ + nano ZnO 6 mg kg⁻¹). Among the treatments, T6 exhibited superior results, with plant height increasing by up to 43% and leaf area by 90.1% compared to the control (T1). SPAD values, fresh weight, and dry weight were notably higher in T5 and T6, with fresh weight in T5 reaching 30.2 g plant⁻¹, an 86.2% increase over T1. Leaf mineral content, particularly zinc (0.31 mg g⁻¹) and calcium (2.91 mg g⁻¹), was significantly enhanced in T5 and T6. Soil analysis revealed improved zinc content (0.77 mg kg⁻¹), organic matter (0.29%), and reduced pH (6.72) in T6. Principal component analysis confirmed the strong association of T5 and T6 with key growth and nutrient parameters. These findings highlight the potential of nano zinc-enriched biochar to mitigate soil degradation and boost agricultural productivity. Open field trials are recommended to confirm the commercial and environmental viability of this approach under diverse conditions.