Soil chemical properties and coffee seedling growth under bioaugmentation of coffee pines agroforestry waste application

Agroforestry systems integrating coffee and pine trees generate large volumes of organic residues, including coffee husks, leaves, and pine litter, which remain underutilized despite their potential as composting materials. This study examined the impact of compost derived from a mixture of coffee–pine agroforestry waste on soil chemical properties and the growth of Coffea canephora (Robusta) seedlings. The experiment was conducted at the Brawijaya University Forest (UB Forest), Malang, Indonesia, using a Randomized Block Design with seven treatments and three replications. Treatments included soil alone and combinations of composted coffee skin, coffee leaves, and pine leaves, with and without bioactivator addition. The composts produced from various agroforestry waste met the Indonesian National Standard (SNI) for solid organic fertilizer and rich in nutrient compared to the initial material, the value for water content (25.8-32.5%), pH (6.76-8.34), N (1.3-1.36%), P (0.44-0.51 mg kg⁻¹), K(1.03-4.05 cmol⁺) and C organic (14.34-24.15%). Results showed a significant difference (p < 0.05) among treatments for soil pH, total nitrogen (N), phosphorus (P₂O₅), potassium (K₂O), and organic carbon (C-organic) and various crop growth parameters. The best plant growth was achieved under treatment K6 (soil + composted coffee leaves + composted pine needles), which produced the highest plant height (20.4 cm) and C-organic value (5.76%), but in term of those effect on leaf length, leaf width and leaf area, the treatment of K3 is better. Regression and correlation analyses indicated that soil phosphorus significantly influenced plant height and stem diameter (R² = 0.33 and 0.24, respectively). The PCA also revealed a distinct group of each treatment and separated the selected parameter into different magnitudes and direction. These findings demonstrate that integrating coffee and pine waste through composting effectively enhances soil fertility and supports sustainable coffee seedling growth in agroforestry systems, while reducing organic waste accumulation and promoting circular bioresource use.