Ecophysiological benefits of industrial organic wastes on alfalfa yield and stress mitigation in saline soils

Abstract

Rising soil salinity and water scarcity demand sustainable solutions to maintain crop productivity. This study evaluated four agro-industrial organic amendments—fish emulsion, neem cake, coffee grounds, and seaweed extract on alfalfa (Medicago sativa) under combined salinity and drought stress, assessing their effects on soil respiration, plant physiology, and yield. Soil CO₂ efflux varied significantly among treatments: coffee grounds induced the highest microbial activity (6.2 μmol m⁻² s⁻¹), suggesting rapid decomposition, while neem cake exhibited stable emissions (3.8 μmol m⁻² s⁻¹), indicating slower organic matter turnover. Fish emulsion showed intermediate dynamics, peaking at 4.8 μmol m⁻² s⁻¹ by week 4, implying phased nutrient release. Physiological responses were treatment-dependent. Fish emulsion enhanced superoxide dismutase (SOD) activity by 35 % under combined stress, whereas coffee grounds increased SOD (28 %) but raised oxidative stress markers by 20 % under water deficit, limiting its applicability. Neem cake and seaweed extract consistently upregulated antioxidant defenses (SOD: 22–25 %; catalase: 18–20 %) across stress levels, with seaweed extract improving photosynthetic efficiency (25 % higher Ci/Ca ratio) in saline soils. All amendments elevated crude fiber content (15–20 %), though protein, fat, and starch responses varied. Yield performance was context-specific: fish emulsion and seaweed extract maximized biomass (35–40 % increase) under water deficit, while neem cake and seaweed extract outperformed controls in moderate salinity (25–30 % gain). Multivariate analysis linked yield improvements to CO₂ assimilation (r = 0.72) and stomatal conductance (r = 0.68), particularly in seaweed and fish emulsion treatments, whereas antioxidant activity correlated with dry matter accumulation (r = 0.65), explaining neem cake's stress resilience. These findings demonstrate that tailored organic amendment selection can optimize productivity, stress adaptation, and soil health, providing a circular economy approach to saline and arid agroecosystems.