Urea merupakan salah satu pupuk sumber nitrogen yang banyak digunakan oleh petani di Kota Tarakan, namun urea memiliki kekurangan yaitu mudah hilang melalui pencucian dan penguapan sehingga ketersediannya bagi tanaman menjadi rendah. Untuk mengurangi kehilangan unsur hara nitrogen dari pupuk urea tersebut maka perlu dibuat modifikasi dalam bentuk pupuk slow release fertilizer (SRF). Penelitian ini bertujuan mengetahui pengaruh formula slow release fertilizer yang dimodifikasi dari urea sebagai sumber N dan bahan organik sebagai bahan pendamping terhadap jumlah nitrogen yang tersedia dalam tanah. Penelitian ini menggunakan rancangan acak lengkap 1 faktor yaitu formula SRF (rasio bahan organik/urea, w/w), terdiri 9 perlakuan yaitu kontrol (K), limbah udang : urea (0:1, F1), limbah udang : urea (1:1, F2), limbah udang : urea (2,5:1, F3), limbah udang : urea (5:1, F4), arang sekam : urea (0:1, F5), arang sekam : urea (1:1, F6), arang sekam : urea (2,5:1, F7), arang sekam : urea (5:1, F8). Perlakuan tersebut diinkubasi selama 0, 14, 21 dan 41 hari, dan pada setiap lama inkubasi diukur pH tanah, C-organik dan jumlah NH4+ tersedia. Hasil penelitian ini menunjukan bahwa formula SRF limbah udang : urea (F4) sangat baik dalam menyediakan unsur hara nitrogen (NH4+) secara bertahap, diukur pada 0, 14, 21, dan 42 hari setelah aplikasi dengan nilai berturut-turut adalah 0,53 % , 0,43 % ,067 % dan 0,11% . Perlakuan formula SRF F4 juga mampu memperbaiki pH dan C-organik organik tanah dengan nilai 6,85 % yang tergolong agak netral, nilai C-organik 8,47% yang tergolong sedang.
Kata Kunci: Pupuk SRF, Arang Sekam, Limbah udang, analisa NH4+

Urea is one of the nitrogen source fertilizers that is widely used by farmers in Tarakan City. However, the shortage of urea is that it is easily vanished through washing and evaporation so as to its availability for plants is low. To reduce the loss of nitrogen nutrients from urea fertilizer, it is necessary to make modifications in the form of slow release fertilizer (SRF) This study aims to determine the effect of SRF formula modified from urea as a source of N and organic matter as a companion material on the amount of nitrogen available in the soil. This study used a completely randomized design with one factor, namely the SRF formula (ratio of organic matter/urea, w/w), consisting of 9 treatments, namely control (K), shrimp waste: urea (0:1,FI), shrimp waste urea (1:1, F2), shrimp waste urca (2.5:1, F3) shrimp waste urca (5:1, F4), husk charcoal urca (0, 1, FS), husk charcoal: urea ( 1, F6), husk charcoal urea (2,5 F7), husk charcoal urca (5: 1, F8). The treatments were incubated for 0, 14, 21 and 41 days, and a teach incubation period of available NH4 the soil pl1, C-organic and the amount of ava were measured. The results of this study indicate that the SRF formula of shrimp waste urea (F4) is very good at providing nitrogen nutrients (NH4+) gradually, measured at 0, 14, 21, and 42 days after application with a value of 0.53% respectively 0.43% 067% and 011% The SRF 14 formula treatment was also able to improve the pH and C organic soil of the soil with a value of 6 85% which was classified as slightly neutral, and the C-organic value of 8.47% which was classified as moderate. Keywords: SRF fertilizer, Husk Charcoal, Shrimp waste, NH4-analysis