Nitrat merupakan salah satu nutrient utama bagi pertumbuhan tanaman dan algae. Nitrat sangat mudah terlarut dalam air dan bersifat tidak stabil sehingga nitrat menjadi tidak tersedia. Sumber utama nitrat berasal dari erosi tanah, pupuk, limbah dan penambatan nitrogen (N). Penambatan N dilakukan oleh bakteri secara simbiotik maupun non simbiotik. Fakultas pertanian memiliki 14 isolat rhizobakteri yang mampu menambat N, tetapi belum diketahui seberapa besar kemampuannya dalam menambat N dalam bentuk nitrat yang mampu disediakan rhizobakteri tersebut. Penelitian ini bertujuan untuk mengetahui seberapa besar kemampuan 14 isolat bakteri penambat N dalam menyediakan nitrat (NO3-). Metode penelitian menggunakan Rancangan Acak Lengkap (RAL) terdiri dari 16 perlakuan dan 2 ulangan yaitu: K0 (Tanah tanpa perlakuan), K1 (Nutrient Broth) P1 (B1(17)) P2 (B1(19)), P3 (B3(10)), P4 (B4(15)), P5 (B3(12)), P6 (B3(16)), P7 (B3(19)) P8 (B3(9)), P9 (B4(12)), P10 (B4(5)), P11 (B5(13)), P12 (B5(15)), P13 (B5(19)) dan P14 (B5(9)). Pada perlakuan P1 sampai dengan perlakuan P14 tanah disiram larutan suspensi isolat bakteri penambat nitrogen dengan kerapatan 10 cfu/mL. Perlakuan K0 yaitu tanah tanpa diberi penambahan nutrient broth (NB) dan bakteri sedangkan K1 yaitu tanah yang diberi penambahan bahan organik berupa nutrient broth (NB) sebanyak 100 mL. Kemudian tanah diinkubasi selama 21 hari. Parameter pada penelitian ini yaitu analisis pH tanah dan analisis nitrat (NO3-) tanah. Hasil penelitian menunjukkan kemampuan isolat bakteri dalam menyediakan N dalam bentuk nitrat berkisar antara 35,06 ppm sampai 45,42 ppm dan isolat bakteri B3(12), memberikan nilai nitrat 45,42 ppm. Hasil penelitian pada parameter pH tanah menunjukkan isolat yang memberikan nilai pH tertinggi yaitu isolat B3(10) (P3) dengan nilai pH 4,69 dan pH terendah 4,20 diperoleh dari isolat B4(12), (P9).
Kata kunci: Nitrogen Tanah, Bakteri Penambat Nitrogen, Tanah Masam

Nitrate is one of the major nutrients for growth of plants and algae. Nitrate is very soluble in water and is very unstable so it becomes unavailable. The main source of nitrate comes from soil erosion, fertilizer, waste and nitrogen (N) accumulation. N uptake is done either by symbiotic or non-symbiotic bacteri. The Faculty of Agriculture of UBT has 14 rhizobacterial isolates capable of digesting N, but it is not yet known how much it can absorb N in the from of nitrates that such rhizobacteria can provide. This study aimed to determine the extent of the ability of 14 N-bonding bacterial isolates to provide nitrate (NO3 - ). This research used a complete randomized design that consisted of 16 treatmenst and 2 replicates. The treatments were K0 (soil without treatmen), K1 (Nutrient Broth) P1 (B1(17)) P2 (B1(19)), P3 (B3(10)), P4 (B4(15)), P5 (B3(12)), P6 (B3(16)), P7 (B3(19)) P8 (B3(9)), P9 (B4(12)), P10 (B4(5)), P11 (B5(13)), P12 (B5(15)), P13 (B5(19)) dan P14 (B5(9)). At P1 to P14 treatments the soil was irrigated whit nitogen-fixing bacterial isolates suspension at a densityof 108 cfu/mL. The treatment of K0 was soil without the addition of Nutrient Broth (NB) and bacterial whereas K1 was soil added with 100 mL organic Nutrient Broth (NB). The soil was then incubated for 21 dasy. The parameters of this study were soil pH analysis and soil nitrate (NO3 - ) analysis.The results showed that the bacterial isolate was able to provide N in the from of nitrates ranging from 35,06 ppm to 45,42 ppm and bacterial isolate B3(12), was able to provide N of 45,42 ppm. The results of soil pH parameters showed that the isolates with the highest pH score was isolate B3(10) , (P3) with pH acore of 4,69 the lowest pH was of 4,20 obtained from isolates B4(12), (P9). Keywords: Soil Nirogen, Nitrogen-Bonding Bacteria, Soil Acidity