Abstract
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.
Published Version
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