Solid anaerobic digestate enhances lemongrass biomass yield

Abstract This study evaluated solid anaerobic digestate as an organic fertilizer to improve lemongrass biomass production. It was hypothesized that increasing doses of solid digestate would (i) increase vegetative growth, (ii) increase total biomass, and (iii) increase total oil yield per plant, up to an agronomic saturation threshold, but (iv) have no effect on oil concentration per plant. Solid digestate derived from a full‐scale anaerobic digester treating mixed organic wastes was surface‐applied at five doses (0, 1.4, 2.9, 5.8, and 11.5 kg m −2 ) to potted lemongrass plants in a replicated outdoor experiment. Plant height, leaf number, tiller number, and harvested biomass were monitored over a 3 month period and essential oil was recovered by steam distillation at final harvest. Digestate application increased plant height, leaf production, tiller number, and total biomass significantly relative to the untreated control. Growth responses increased proportionally up to 5.8 kg m −2 , with a saturation pattern occurring up to the maximum dose applied. No evidence of growth suppression or toxicity was observed, even at the highest concentration. Total essential oil yield increased proportionally with leaf biomass (approximately 15 mL kg⁻¹), whereas oil yield per unit fresh biomass remained consistent across treatments, indicating that solid digestate primarily stimulated structural growth rather than altering oil concentration. These results demonstrate that solid digestate is a viable organic fertilizer for lemongrass cultivation. As a residual byproduct of anaerobic digestion, digestate valorization provides a productive use for this waste stream while recycling nutrients to support soil fertility and future crop production.