Circular Nutrient Inputs for Red Chili: Eggshell Powder and Rice-Wash Water

Household food residues are increasingly considered low-cost nutrient resources, yet their effectiveness depends on nutrient form, release rate, and crop demand. This study evaluated the individual and combined effects of eggshell powder and fresh rice-wash water on red chili (Capsicum annuum L.) growth, phenology, and yield. A 3 × 3 factorial randomized block design with three replications was conducted in Medan, Indonesia, from April to July 2026. Eggshell powder was applied at 0, 10, and 20 g plant-1, while rice-wash water was applied at 0, 250, and 350 mL plant-1. Data were analyzed by ANOVA followed by Duncan's multiple range test at 5% when significant. Eggshell powder did not significantly affect any measured trait. Rice-wash water significantly increased stem diameter at 3 weeks after planting (2.60-2.65 mm versus 2.40 mm in the control), advanced flowering to 34.89 days at 350 mL plant-1 compared with 37.78 days in the control, and shortened harvest age to 68.00 days compared with 69.33 days. However, these effects did not persist into significant differences in fruit number or fruit weight. No eggshell × rice-wash-water interaction was detected. The findings reveal a temporally specific response: readily available nutrients from fresh rice-wash water influenced early growth and crop phenology, whereas untreated eggshell CaCO3 was apparently too slowly available to generate a yield response within one crop cycle. Synchronizing residue processing and nutrient release may therefore be more important than simply combining household-waste inputs.