<![CDATA[The third producing oil palm plant or TBM III is an oil palm plant that is 36 months old and is a potential initial plant for producing palm oil. This research aims to identify the diversity of soil mesofauna in the PTPN III Plantation during the TBM III growth phase. The research was carried out at Perkebunan Nusantara 3 Aek Nabara Selatan in December 2023. The sample was determined using purposive random sampling based on slope differences, namely 0-5% and 5-15%. For one type of slope, 4 different observation locations were taken at random so that a total of 8 sample units were obtained. Each observation sample was made into a cube-shaped monolith with dimensions of 30 x 30 x 40 cm. The results of meso and macrofauna observation data were tested for differences in slope of 0-5% and 5-15% based on the t test at the 5% level. The research results show that a slope of 0-5% has a larger fauna distribution than a slope of 5-15%. This indicates that flatter land has greater macro and mesofauna activity because the area is covered by plant remains. On slopes of 0-5% to 5-15% the macrofauna is dominated by ants and earthworms. Key words: soil mesofauna, species diversity, TBM III INTISARITanaman sawit menghasilkan ketiga atau TBM III merupakan tanaman kelapa sawit yang berumur 36 bulan dan merupakan tanaman awal yang potensial untuk memproduksi sawit. Penelitian ini bertujuan untuk mengidentifikasi keanekaragaman mesofauna tanah di Perkebunan PTPN III pada fase pertumbuhan TBM III. Penelitian dilaksanakan di Perkebunan Nusantara 3 Aek Nabara Selatan pada Desember 2023. Penentuan sampel dilakukan secara purposive random sampling berdasarkan perbedaan kelerengan yaitu 0-5% dan 5-15%. Pada satu jenis kelerengan diambil 4 lokasi pengamatan berbeda secara acak sehingga diperoleh 8 satuan sampel secara keseluruhan. Tiap sampel pengamatan dibuat monolith berbentuk kubus dengan dimensi 30 x 30 x 40 cm. Hasil data pengamatan meso dan makrofauna diuji perbedaan kelerengannya 0-5% dan 5-15% berdasarkan uji t pada taraf 5%. Hasil penelitian menunjukkan bahwa kelerengan 0-5% memiliki sebaran fauna yang lebih besar dibanding dengan kelerengan 5-15%. Hal ini mengindikasikan bahwa lahan yang lebih datar memiliki aktivitas makro dan mesofauna yang lebih besar karena daerahnya ditutupi oleh sisa tanaman. Pada kelerengan 0-5% hingga 5-15% makrofauna didominasi oleh semut dan cacing tanah. Kata kunci: mesofauna tanah, keragaman jenis, TBM III]]>
