Synergistic effect of garbage enzyme and FeSO₄ on iron availability and radish (Raphanus sativus L.) productivity in calcareous soil.
Abstract
Iron deficiency chlorosis severely limits crop productivity in calcareous soils, while fruit and vegetable waste accumulates globally as an environmental burden. This study investigated whether garbage enzyme (GE), a fermented fruit waste product, can synergistically enhance the efficiency of conventional FeSO4 fertilizer in a calcareous soil (pH 7.9, CaCO3 18.4%). A greenhouse experiment was conducted with radish using a 2 × 3 factorial design: GE at 0 or 3.2% (v/v) and FeSO4.7H2O at 0, 11.2, and 22.3 mg Fe per kg soil. Each treatment had four replicates. Co-application of GE (3.2%) and FeSO4 (22.3 mg/kg) increased DTPA-extractable soil iron by 364% compared to the control (from 2.8 to 13.0 mg/kg). Leaf chlorophyll content (SPAD index) improved by 29.9%, and tuber dry weight increased by 74.1%. Root dry weight showed a 144.5% increase. Soil pH remained stable between 7.8 and 7.9, and electrical conductivity between 0.8 and 0.9 dS/m, with no significant differences among treatments. Available potassium in soil reached 367 mg/kg in the combined treatment, 49% higher than the control (247 mg/kg). For phosphorus, soil available P decreased when GE and high FeSO4 were applied together, while plant tissue P concentration in both leaves and tubers was highest in the same treatment. Garbage enzyme synergistically enhances FeSO4 efficiency in calcareous soil, improving iron availability, chlorophyll synthesis, and tuber yield without altering bulk soil pH or EC. The concurrent increase in root biomass (144.5%) may explain the higher plant P uptake despite lower soil P availability (likely due to Fe-P complexation), suggesting improved root-mediated acquisition. This circular-economy approach simultaneously valorizes fruit waste and addresses iron deficiency, though direct mechanistic evidence (e.g., spectroscopic confirmation of Fe-organic complexes) and optimization of GE concentration require further investigation.