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

Abstract Conversion of natural forests to agricultural land or other uses is still common in tropical regions. However, over time, when agriculture productivity decreases, land will be abandoned of fallowed by farmers. Agroforestry with dense tree canopy cover can reduce the population of Imperata cylindrica (alang-alang), increasing organic material input from litter and dead roots followed by a higher density of soil organisms. The purpose of this study is to evaluate the role of agroforestry in improving soil health in Imperata grassland by evaluating earthworm density as an indicator. This research was conducted in July-August 2024 in the Solok Regency, West Sumatra on Andisols at approximately 1500 m above sea level. We measured the microclimate, canopy cover, basal area, standing litter, as well as earthworm diversity and population density. Earthworm sampling was done using the monolith technique from TSBF (Tropical Soil Biology and Fertility). Land currently under annual crops was compared with Imperata grassland, grassland plots converted to coffee-based agroforestry systems 1-3, 4-6 or >7 years ago, old multistrata agroforestry system (AFMT), and remnant secondary forest in the same landscape. The results showed that earthworm densities were highest in AFMT, less than half as much in the Imperata grasslands and close to zero in currently cropped land, but also in the remnant secondary forest. Conversion of grassland to agroforestry appears to initially (1-4 years) reduce earthworm populations before they recover, but populations don’t reach the AFMT level in 5-7 year old plots. A number of relationships was explored that may help understand these results. Old multistrata agroforestry system (AFMT) have a canopy cover od 47% (compared to 69% for the remnant forest) and increase humidity and reduced air and soil temperature compared to open [ields. Standing litter necromass was highest in AFMT, followed by agroforestation of Imperata grasslands. Within these results, earthworm presence is not related to tree basal area or canopy cover, but variation in standing litter accounts for 28% of variation in earthworm numbers. Reclaiming degraded Imperata grassland land with an agroforestry system is effective, as it increases land cover, provides high litter inputs, and creates habitats for earthworms, thereby improving soil health.