Judul: Effect of NPK 17-6-25 Fertilizer Dosage and  the Potential of Bacillus subtilis on Growth and Production of Sweet Potato (Ipomoea batatas L.)
Abstrak: Peningkatan kebutuhan ubi jalar tidak sebanding dengan produktivitas ubi jalar. Inovasi pemupukan majemuk yang secara khusus untuk produksi ubi jalar diperlukan dalam mendukung efisiensi budidaya. Pupuk NPK 17-6-25 sudah terbukti efektif terhadap pertumbuhan dan produksi ubi kayu, hal ini memberi peluang penggunaannya dalam pemupukan ubi jalar. Penelitian dilaksanakan di Kebun Percobaan Sawah Baru, Departemen Agronomi dan Hortikultura dan Laboratorium Pasca Panen, Institut Pertanian Bogor dari bulan Oktober 2023 hingga Februari 2024. Penelitian menggunakan rancangan kelompok lengkap teracak dua faktor yaitu varietas ubi jalar dengan 2 taraf Antin 3 dan Beta 1, serta dosis pemupukan NPK 17-6-25 0 kgha-1, 100 kgha-1, 200 kgha-1, 300 kg ha-1 dan 1 taraf pemupukan Bacillus subtilis 2,5 ml l-1. Hasil penelitian menunjukkan bahwa pertumbuhan vegetatif varietas Beta 1 lebih baik dari Antin 3. Perlakuan dosis pupuk NPK 17-6-25 100 – 300 kg ha-1 memberikan peningkatan hasil produksi dengan bobot umbi per petak sebanyak 21,54–24,81 kg dan bobot total umbi sampel sebanyak 6,39 kg. Kedua varietas ubi jalar memberikan respon yang berbeda terhadap perlakuan Bacillus subtilis. Dosis optimum pemupukan NPK 17-6-25 pada varietas Antin 3 sebanyak 235,35 kgha-1, dan untuk varietas Beta 1 sebanyak 176,75 kgha-1., The increasing demand for sweet potatoes is not proportional to their productivity. Innovation in compound fertilization specifically for sweet potato production are needed to support cultivation efficiency. NPK 17-6-25 fertilizer has proven effective for the growth and production of cassava, offering potentialfor its use in sweet potato fertilization. The research was conducted at the Sawah Baru Experimental Farm, Departement of Agronomy and Horticulture and Post–Harvest Laboratory, Bogor Agricultural University, from October 2023 to February 2024. The study used a two-factor randomized complete group design with sweet potato varieties (Antin 3 and Beta 1), and NPK 17-6-25 fertilizer doses of 0 kg ha-1, 100 kg ha-1, 200 kg ha-1, 300 kg ha-1, and one level Bacillus subtilis treatment at 2,5 ml l-1. The results showed that the vegetative growth of Beta 1 was better than that of Antin 3. Treatment with NPK fertilizer 17-6-25 doses of 100 300 kg ha-1 increased production yield, with tuber weights per plot ranging from 21,54 to 24,81 kg and total sample tuber weight of 6,39 kg. The two sweet potato varieties responded differently to Bacillus subtilis treatment. The optimum dose of NPK 17-6-25 fertilizer for the Antin 3 variety was 235,35 kg ha-1 and for the Beta 1 variety, it was 176,75 kg ha-1.
Keyword: produktivitas, antin 3, beta 1, umbi layak pasar

Judul: Pengaruh Dosis Pupuk NPK 15-10-12 dan Potensi Bacillus subtilis terhadap Pertumbuhan dan Produksi Hasil Tanaman Ubi Jalar.
Abstrak: Kebutuhan terhadap ubi jalar yang terus meningkat tidak sebanding dengan produksi tanaman yang cenderung fluktuatif. Penggunaan pupuk majemuk bersubsidi menjadi salah satu alternatif untuk meningkatkan produksi dan efisiensi kegiatan budidaya, akan tetapi belum ada pupuk yang disubsidi untuk tanaman ubi jalar. Perlu diketahui apakah substitusi pupuk subsidi lain seperti NPK 15-10-12 yang diperuntukkan pada tanaman jagung juga mampu meningkatkan produksi tanaman ubi jalar. Penelitian dilaksanakan bulan November 2023 hingga Januari 2024 di Kebun Percobaan Sawah Baru. Rancangan percobaan yang digunakan RKLT dua faktor yaitu varietas (Antin3, Beta1) dan dosis. Dosis pemupukan terdiri dari lima taraf yaitu pupuk NPK 15-10-12 0, 100, 200, 300 kg ha-1 , dan Bacillus subtilis 2,5 ml L -1 dengan volume semprot 500 L ha-1 . Hasil penelitian menunjukkan varietas Antin 3+Bacillus subtilis menghasilkan jumlah umbi layak pasar tertinggi yaitu 50% dan bobot umbi per petak tertinggi yaitu 22,13 kg. Kombinasi varietas Antin 3+200 kg ha-1 NPK 15-10-12 menghasilkan umbi dengan kemanisan tertinggi yaitu 11,16 °brix. Dosis rekomendasi NPK 15-10-12 pada varietas Antin 3 yaitu 179,08 kg ha-1 , dan 131,86 kg ha-1 pada varietas Beta 1., The increasing demand for sweet potato is not proportional to the fluctuating crop production. The use of subsidized compound fertilizers is one alternative to increase production and efficiency of cultivation activities, but there is no subsidized fertilizer for sweet potato crops. It is necessary to know whether the substitution of other subsidized fertilizers such as NPK 15-10-12 which is intended for corn crops is also able to increase sweet potato crop production. The research was conducted from November 2023 to January 2024 at Sawah Baru Experimental Farm. The experimental design used RKLT two factors, namely variety (Antin3, Beta1) and dose. The fertilization dose consisted of five levels, namely NPK 15-10-12 fertilizer 0, 100, 200, 300 kg ha-1, and Bacillus subtilis 2,5 ml l-1 with a spray volume of 500 l ha-1 . The results showed that the Antin 3 variety + Bacillus subtilis produced the highest number of marketable tubers at 50% and the highest tuber weight per plot at 22,13 kg. The combination of Antin 3 variety + 200 kg ha-1 NPK 15-10-12 produced tubers with the highest sweetness of 11,16 °brix. Recommended dose of NPK 15-10-12 on Antin 3 variety is 179,08 kg ha-1 , and 131,86 kg ha-1 on Beta 1 variety.
Keyword: Antin 3, Beta 1, productivity

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.
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