Judul: Pembuatan Pupuk Urea Bersalut Gibsum (Gypsum Coated Urea, GCU) dan Pengaruhnya terhadap Pertumbuhan Jagung (Zea mays).
Abstrak: Urea (CO(NH2)2) merupakan jenis pupuk nitrogen yang paling banyak ditemui dipasaran dan digunakan oleh petani di Indonesia. Sifat higroskopis yang dimiliki oleh pupuk urea menyebabkan pupuk ini mudah larut dalam air dan mudah tercuci keluar dari sistem tanah, akibatnya pemupukan menjadi sangat tidak efisien. Salah satu upaya untuk mengurangi kehilangan N akibat pencucian yaitu dengan memodifikasi sifat fisik pupuk urea dengan mengubah menjadi pupuk lambat tersedia (slow release). Halangan fisik pada pupuk slow release, dapat digunakan untuk memperlambat interaksi antara pupuk urea dengan air sehingga urea akan lebih tahan pelarutan oleh air dan mengurangi kehilangan N melalui pencucian. Tujuan penelitian ini adalah : (1) Membuat pupuk urea bersalut gibsum (Gypsum Coated Urea, GCU), (2) Mengukur konsentrasi N-NH4 + dan N-NO3 - dari pupuk GCU pada percobaan pencucian, (3) Menentukan pengaruh pupuk GCU terhadap pertumbuhan dan serapan nitrogen, serta kalsium pada jagung. Hasil penelitian menunjukkan bahwa diperoleh empat jenis pupuk GCU berbentuk granul ukuran 3-5 mm dengan kandungan nitrogen sebesar 33.36% (S1) , 30.97% (S2), 31.51% (M1), dan 29.73% (M2). Empat jenis pupuk tersebut berkarakter sebagai slow release karena dapat mengurangi pencucian nitrogen dalam bentuk ammonium dan nitrat. Berdasarkan data pertumbuhan dan analisis serapan hara tanaman menunjukkan bahwa bentuk slow release yang diperoleh berpengaruh nyata terhadap pertumbuhan tinggi jagung pada 2 hingga 5 minggu setelah tanam.
Keyword: kehilangan nitrogen, pencucian, pupuk lambat tersedia

Judul: Formulasi Pupuk Nitrogen Lambat Tersedia dari Bahan Urea, Zeolit, dan Asam Humat serta Pengaruhnya terhadap Pertumbuhan Jagung
Abstrak: The quality of agricultural land in Indonesia was declining progressively and it affect to the decrease of crop production. It is well known that N fertilizer is inefficient due to evaporation into atmosphere and leached into the grown water. The objectives of this research were to study the formulation of slow release N-fertilizer made from urea, zeolite, humic acid, and polymer; to study the pattern of nitrogen release from this modified slow release fertilizer; and to evaluate the effect of modified slow release fertilizer on corn growth. The ratio of urea and zeolite used in this experiment was prepared with the ratio of urea (U) and zeolite (Z) 7:3 and 8: 2, humic acid (HA) of 2 and 2.5% and arabic gum as the binding material. The modified fertilizers were put into the percolation column. The volume and concentration of ammonium-N and nitrate-N were collected and measured during one month percolation with Kjeldahl methode. The modified fertilizers then used to evaluate the effect of the fertilizers on growth of corn in greenhouse experiment. The results showed that the composition of the six N fertilizer were prepared by coating with zeolite, humic substance, and gum arabic characterized as a slow release fertilizer. Zeolite, humic substance, and gum arabic or combinations there of as coating agent is able to reduce the peak release of N-NH4+ and N-NO3- and change the pattern of release to be still available until the end of the test period. Based on the data of corn’s growth, slow release fertilizer forms obtained did not match the corn crop N requirement in accordance with the physiological growth so that the best growth is obtained only by urea which has a high solubility. Humic substance influential in terms of the physiological properties of corn compared to its role as an encapsulation on slow release fertilizer.
Keyword: ammonium-N, humic acid, nitrate-N, slow release fertilizer, zeolite

Judul: Hamiltonian formulation for linear waves motion in two layers fluid
Abstrak: The surface wave could be considered as a wave that separates two fluids, namely water and air. Based on this assumption, it is introduced the interfacial wave, a wave between two layers of fluid with different density. The formulation of interfacial waves motion begins with deriving the base equation of irrotational ideal fluid. Furthermore, according to irrotational fluid assumption, the base equation can be stated in velocity potential. In this derivation, the fluids domain is assumed to be restricted by rigid lid boundary conditions, both at the upper and lower limit. Therefore, the interfacial waves motion can be explained in a hamiltonian formulation. In the hamiltonian formulation, total energy is defined as the sum of kinetic and potential energy. The hamiltonian system is obtained from reduction of kinetic energy by using the Dirichlet Neumann Operator. The resulted kinetic energy equation is nonlinear. Therefore, this form is linearized by first part of the Taylor expansion. This linearization gives a dispersion relation of linear wave. Based on this dispersion relation, the phase speed of the linear wave depends on the density ratio of the two layers fluid.
Keyword: