Phenological and nutritional dynamics of Tithonia diversifolia across harvest intervals in tropical mid‑altitudes

Abstract As a protein-bank shrub for cut-and-carry use within silvopastoral agroforestry, Tithonia diversifolia can stabilize on-farm protein supply, yet links between its phenology, forage quality, and yield remain scarce. This study evaluated morphological (plant height, stem length and diameter, number of leaves and stems, leaf-to-stem ratio), chemical (DM, CP, aNDFn, ADFn, ADL, EE, NSCn, OM, NE L ), and yield (biomass and nutrient yields per cut and per year) responses of T. diversifolia across five harvest intervals (20, 30, 40, 50, and 60 days) under mid-altitude tropical conditions to identify phenological indicators of optimal harvest time. Twelve 36 m 2 plots were arranged in a randomized block design (three slope positions) and monitored using repeated measures. Growth stage significantly affected nutrient concentrations (P < 0.05), nutrient yields, and morphological traits (P < 0.0001). Crude protein declined from 268 to 134 g·kg –1 DM, while aNDFn, ADFn, and lignin increased; NE L followed a cubic pattern, and NSCn peaked at 20 and 50 days. Biomass and nutrient yields per cut increased with age, but annual yields of DM, CP, NSCn, OM, and lignin peaked at 40 days, as longer regrowth intervals reduced harvest frequency. Plant height, stem length, and diameter correlated negatively with CP and NE L but positively with nutrient yields (|r| ≥ 0.80; P < 0.01). The optimal harvest stage was 40 days, when plant height was 122 cm, stem length 73 cm, and stem diameter 8.2 mm, balancing forage quality and productivity. These indicators offer low-cost tools to optimize cutting schedules and enhance silvopastoral sustainability.