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Andisol soils affected by the eruption of Mount Sinabung have different levels of ash thickness, each thickness has a different microbial activity and nutrient status. The aim of this research was to find non-symbiotic nitrogen-fixing bacteria isolates in several volcanic ash thicknesses. This research was conducted at the Soil Biology Laboratory, Faculty of Agriculture, University of Sumatera Utara. Isolation of non-symbiotic nitrogen-fixing bacteria was carried out using a nitrogen-free growth medium, Jensen medium. The results indicated that 7 bacterial isolates were able to grow on nitrogen-free medium, these isolates had different shapes (B1- B7). In the land which is not covered with ash there are 2 isolates, in the soil covered in thin ash (<2 cm) there are 2 isolates, in the soil covered in medium ash (2-5 cm) there are 2 isolates and in the soil covered in thick ash (> 5 cm) there are 1 bacterial isolate.

The important properties to overcome the corrosion are safe, available, biodegradable, low cost, and environmental friendly. Gambier leaves extract is one of the inhibitor that have environmental friendly properties. This study aims to determine the effectiveness of extract using ethanol-water to reduce the corrosion rate. Soaking of ferrous iron plate samples in seawater media have done for corrosion test. Agitator and aerator motors at turn-on and conducted a series of immersion with varying contact time 5, 10, 15, and 20 days. After the time up next ferrous iron plate samples were cleaned, dried, and weighed. Experiment was repeated by adding a inhibitor heavy leaves gambier extract with varying leaves gambier extract, 1000, 3000, and 5000 ppm. Soaking iron plate samples performed at varying pH at 3(acid), 6 (netral), and 9 (alkaline). Calculation is then performed and the rate of corrosion inhibition efficiency gambier leaves extract with ethanol-water solvent. On the immersion of iron plate without inhibitor, the result that the longer the contact time, the weight of the iron plate was reduced. The results showed the addition of inhibitors of leaves extract gambier with ethanol-water solvent into the corrosive media can reduce the rate of corrosion. Inhibitor of leaves extract gambier using ethanol-water solvent effective to reduce the rate of corrosion inhibitor at a concentration of 5000 ppm and contact time of 20 days with the lowest value of the corrosion rate is 0.000503 g/cm² days in seawater media at initial pH 7.9. Gambier extracts gave greatest inhibition efficiency about 60.345% obtained at a concentration of 5000 ppm inhibitor and 20 days contact time.

Abstract. Sembiring M, Munawaroh H, Mukhlis, Hidayat B, Sabrina T. 2021. Soil macrofauna diversity in andisol after eight years of Mount Sinabung eruption in Sumatra, Indonesia. Biodiversitas 22: 3024-3030. The eruption of Mount Sinabung resulted in volcanic ash covering the soil of various thicknesses. That will affect the population and diversity of macrofauna in it. This research aimed to determine the Andisol soil macrofauna in Karo District with various thicknesses of volcanic ash covering from Mount Sinabung. This research was conducted in May 2019. Plots were placed in four locations, Location I: processed land (0 cm), Location II: Land covered by thin ash (?2 cm), Location III: Land covered by medium ash (2-5 cm), Location IV: Land covered by thick ash (?5 cm). Sampling was conducted by using the Pitfall trap, Monolith squared, and Hand sorting methods. The research results indicated that the thicker the volcanic ash covering the soil surface, it would reduce soil moisture, soil water content, organic C, and soil pH, but on the other hand, increase the soil temperature. A total of 20 species were able to live on the Andisols affected by the eruption of Mount Sinabung.

ABC adalah salah satu perusahaan yang berusaha di bidang manufaktur penghasil gripper rubber seal. Perusahaan ini memiliki masalah dalam tata letak lantai produksinya yaitu  terdapat crossmovement dan jarak pada beberapa stasiun juga terlalu jauh yang menyebabkan aliran bahan terganggu. Permasalahan ini dapat diselesaikan dengan melakukan perbaikan tata letak lantai produksi menggunakan metode CORELAP dan ALDEP kemudian dilakukan simulasi dengan software Flexsim. Penelitian ini bertujuan untuk merancang tata letak fasilitas usulan yang dapat meminimalkan jarak perpindahan bahan dengan  membandingkan efisiensi momen perpindahan tataletak aktual dengan tataletak yang diusulkan. Hasil dari penelitian ini menunjukkan adanya penurunan total momen perpindahan pada lantai produksi PT. ABC dari 14.495,08 meter/bulan menjadi 5930,19 meter/bulan dengan menggunakan algoritma CORELAP dan sebesar 7.369,7 meter/bulan pada algoritma ALDEP. Efisiensi jarak pada layout usulan juga meningkat dari 53,67% menjadi 93,74% pada algoritma CORELAP dan 78,18% pada algoritma ALDEP. Setelah dilakukan simulasi untuk mencari metode yang terbaik, didapatkan layout usulan yang terpilih merupakan layout hasil algoritma CORELAP dengan kilometers traveled per day 1,9 km/hari.

The aim of this research is to observe the impact of various thicknesses of volcanic ash and different vegetation on microorganism populations in Andisol affected by the eruption of Mt. Sinabung in NamanTeran Sub-district, Karo district, which was affected by the eruption of Mt. Sinabung after 5 years of eruption which is distinguished by several ash thicknesses, namely: A0: 0cm (already processed), A1: <2 cm (thin), A2:> 2-5 cm (moderate), A3:> 5 cm (thick) with annual plant vegetation and grass vegetation. Soil sampling was using the survey method. Calculation of total soil microorganisms was done by the Total Plate Count method. The results indicated that the higher the pH, C-organic, humidity and temperature, the more microorganism population, also different thickness of ash and vegetation affected the number of microorganism population.

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