Nutrient-Enriched Poultry-Litter Biochar for Circular Nutrient Management: Vegetative and Canopy Responses of Container-Grown Echinacea purpurea

Nutrient-enriched poultry-litter biochar may support circular nutrient use. The aim of this exploratory 9-month container study was to compare vegetative, leaf-optical and canopy responses of Echinacea purpurea (L.) Moench ‘White Swan’ to two complete nutrient-enriched poultry-litter biochar treatments (PLB95:5 and PLB85:15), applied at 5 or 10 g pot−1 (n = 4). PLB95:5 and PLB85:15 refer to urea–ammonium nitrate solution (UAN-28; 28% N) to liquid vermicompost mass proportions of 95:5 and 85:15, respectively, within the nutrient component; nominal N additions were 18 and 60 g N kg−1 original biochar, respectively. At 7 months, leaf number differed among treatments (p = 0.000839; q = 0.0117), with PLB85:15 at 10 g pot−1 producing 64.8 leaves plant−1 versus 33.0 in the control. Pot-normalised projected foliage area differed at 4 months (p = 0.0061; q = 0.0424); the 7-month effect (Welch’s ANOVA, p = 0.0204) did not remain significant after broader correction (q = 0.0954). Simple Ratio Pigment Index (SRPI) at 4 months and Water Band Index (WBI) at 7 months remained significant after spectral correction. Fresh mass at 9 months did not differ (p = 0.245). The results represent exploratory whole-treatment comparisons and support nutrient-matched testing within a circular nutrient-management pathway.