Seasonal Evaluation and Effects of Poultry Litter-Based Organic Fertilization on Sustainable Production and Secondary Metabolism of Cuphea carthagenensis (Jacq.) J. F. Macbr

To ensure the quality and efficient access of the population to plant-derived resources, research on the sustainable cultivation of medicinal species is of great importance, and the present study aimed to evaluate the influence of poultry litter-based organic fertilization and seasonality on plant growth, soil health (quality), and secondary metabolism of Cuphea carthagenensis. Plants were cultivated during the summer and autumn/winter seasons in a randomized design with five poultry litter application rates (0, 10, 20, 30, and 40 t ha−1) and three replications per plot field (1 × 2 m). The parameters evaluated included soil health, plant biomass, nutrient content, extract yield from the aerial parts, and chemical composition. In the summer, soil bioindicators (microbial biomass carbon and basal respiration) increased with the addition of poultry litter, although plant biomass was not affected by the season. Plant nutrient levels, particularly N and P, increased under poultry litter application rates of 30 t ha−1 and higher. Under these conditions, the highest extract yield from the aerial parts was obtained at a rate of 40 t ha−1. During autumn/winter, poultry litter increased significantly soil microbial biomass carbon, plant biomass, and N and P contents, resulting in an 11.07% increase in extract yield at a rate of 20 t ha−1. Phytochemical analysis of the extracts identified 29 compounds, predominantly quercetin derivatives. Overall, the findings demonstrate that the sustainable cultivation of C. carthagenensis under organic fertilization enhances soil health, plant biomass, and extract yield. These findings highlight the potential of organic nutrient management as a promising strategy for advancing sustainable medicinal plant production and meeting societal demands for natural bioactive resources.