Agroforestry for Reclamation of Imperata Grassland: Earthworm as indicator for soil health

This study evaluates the role of agroforestry systems in the restoration of degraded grasslands dominated by Imperata cylindrica (alang-alang) in the Solok Regency, West Sumatra (Indonesia), on Andisols at approximately 1500 m altitude, using earthworm density and biomass as indicators of soil health. Thirty-two plots representing eight land uses were compared: intensive and extensive agriculture, Imperata grassland prior to restoration, coffee agroforestry systems of varying ages (1–3, 4–6, and >7 years), old multi-strata agroforestry (AMAF), and remnant secondary forest. Microclimate, canopy cover, basal area, and standing litter were measured, and earthworms were sampled using the TSBF monolith technique at three depths. The results showed that earthworm densities were highest in the AFMT (up to 370 individuals/m² and 130.52 g/m² of biomass), less than half in the Imperata grasslands, and almost nonexistent in cultivated land and the remaining forest. Conversion from grassland to agroforestry initially reduces populations (1–4 years) before they recover, not reaching AFMT levels in plots after 5–7 years. Earthworm presence was not associated with basal area or canopy cover, but variation in standing litter explained 28% of the variation in earthworm numbers. The authors conclude that restoring degraded Imperata grasslands with agroforestry systems is effective because it increases soil cover, provides high litter inputs, and creates habitats for earthworms, thus improving soil health.