Earthworm Population and Diversity in Smallholder Oil Palm Plantations under Conventional and Semi-Organic Systems in Labuhan Batu Regency

Oil palm (Elaeis guineensis Jacq.) is an important plantation commodity for Indonesia’s economy. Most farmers still rely on conventional farming systems, which have negative impacts on both microfauna and macrofauna, particularly earthworms. This study aimed to analyse the differences in population and diversity of earthworms under conventional and semi-organic farming systems in oil palm plantations. The research was conducted in 18 smallholder oil palm plantations over 10 years old in Labuhan Batu Regency, North Sumatra, from October 2023 to April 2024. A total of 18 productive plantation sites were surveyed, with three samples collected from each site, resulting in 54 samples (n = 54). The study employed a survey method with purposive sampling. The results showed that in the semi-organic farming system, earthworm population parameters were 149.5% higher compared to the conventional system, while earthworm diversity was 60% higher under the semi-organic system than under the conventional one. Soil parameters that were positively and significantly correlated with earthworm population were soil pH (P = 0.484*, α = 0.05) and sand content (P = 0.536*, α = 0.05). Meanwhile, sand content also showed a positive and significant correlation with earthworm diversity (P = 0.588*, α = 0.05).