From biomass to pelletized fertilizer: a Gliricidia sepium-based Green-N system for sustainable organic agriculture

Abstract

Gliricidia sepium biomass is a locally available nitrogen-rich resource for organic systems, but processing may alter nutrient composition, composting dynamics, and pellet mechanical resistance. This study produced eight Green-N formulations from leaves and/or stems using drying and pelletization, aerobic composting for 5–120 days, or fermentation, and evaluated their physicochemical properties and pellet hardness. Two independent 120-day composting trials were also conducted in 2021 (autumn/winter) and 2022–2023 (spring/summer) to quantify temperature, moisture, dry-matter loss, ammonia volatilization, and nitrogen transformations. Composting duration significantly affected the C/N ratio, pH, nutrient concentrations, and pellet hardness. N-LS30 showed greater hardness (6.26 kg-force (kgf)) than all other formulations, whereas N-LS5, N-LS120, and N-LS formed the lowest statistical group. For total nitrogen, N-LS5 and N-LS15 formed the lower statistical group (2.2–2.3%), while the remaining formulations evaluated for chemical composition did not differ significantly. Across the two composting trials, dry-matter losses reached 61.55% and 62.85%, and ammonia volatilization in 2021 was concentrated during the first 45 days. The C/N ratio declined during composting and nitrate accumulated progressively, indicating stabilization. These results show that processing time can be used to obtain Gliricidia-derived organic inputs with distinct physical and nutrient-release characteristics, with 30-day composting favoring pellet resistance and longer composting favoring material stabilization. At 120 days, N-LS120 contained 41.80% C, 3.70% N, 0.27% P, 1.56% K, 1.53% Ca, and 0.85% Mg on a dry-mass basis.