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: The Growth and Tuber Yield of Sweetpotato (Ipomoea batatas L.) Ase Kapas at Various Rates of Nitrogen Fertilizer
Abstrak: Ubijalar merupakan tanaman pangan penting di Indonesia. Produktivitas ubijalar dapat dipengaruhi oleh pemupukan. Tujuan penelitian ini yaitu menentukan dosis nitrogen bagi pertumbuhan dan produksi ubijalar Ase Kapas. Penelitian dilakukan pada bulan Januari sampai Juli 2020 di Kebun Percobaan Cikabayan IPB dengan rancangan kelompok lengkap teracak dengan 3 ulangan. Dosis N yang diaplikasikan yaitu 0; 22,5; 45; 67,5; dan 90 kg ha-1 . Bahan tanam yang digunakan yaitu bagian stek pucuk. Curah hujan selama penelitian cenderung tidak sesuai dengan kondisi optimal pertumbuhan ubijalar. Pada tanah dengan kandungan nitrogen berstatus sedang (0,29% setara dengan 174 kg ha-1 ), dosis N tidak berpengaruh signifikan terhadap perubahan panjang dan diameter sulur, jumlah daun dan cabang, panjang dan diameter umbi, serta bobot basah dan kering umbi dan brangkasan. Pada tanah dengan kandungan N total sedang, dosis 0 kg N ha-1 dapat diaplikasikan untuk mendukung pertumbuhan dan produksi yang baik bagi ubijalar klon Ase Kapas., Sweetpotato is an essential crop plant in Indonesia. The productivity of the sweetpotato could be affected by fertilization. The objective of this research is to assess optimal nitrogen rate for growth and root yield of sweetpotato Ase Kapas. The experiment was conducted at IPB University experimental field Cikabayan from January to July 2020 used randomized complete block design with 3 replications. The level of nitrogen fertilizer consists of 0; 22,5; 45; 67,5; and 90 kg ha-1 . The planting material is the vine cuttings. The rainfall during this experiment tends to be insufficient as climate requirements. In the soil with moderate N content (0.29% equal to 174 kg ha-1 ), nitrogen had no significant effect on the growth of length and diameter of main stem, the amount of leaves and secondary stems, length and diameter of storage roots, wet- and dry-weight biomass of storage roots and aboveground part. In the soil with a moderate N total, dose of 0 kg N ha-1 could be applied to support good growth and yield of sweetpotato clone Ase Kapas.
Keyword: produktivitas, suplai nitrogen, umbi, Urea, nitrogen supply, storage root, 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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