Judul: Analysis of the distribution of soil organic-C in PT Perkebunan Buah Subang
Abstrak: Lahan pertanian yang digunakan secara terus-menerus dapat menurunkan kesuburan tanah. Salah satu indikator kesuburan tanah adalah bahan organik tanah. Pengukuran kadar bahan organik dapat ditentukan dengan menganalisis kandungan C-organik tanah. Penelitian ini bertujuan mempelajari sebaran kandungan Corganik dalam tanah di PT Perkebunan Buah Subang dan faktor-faktor yang mempengaruhinya, meliputi kondisi lingkungan dan karakteristik tanah. Pengambilan contoh tanah dilakukan secara komposit dengan memperhatikan perbedaan kemiringan lereng dan tipe penggunaan lahan. Hasil penelitian menunjukkan kandungan C-organik tertinggi yaitu 3.13% terdapat pada penggunaan lahan hutan bambu, kemiringan 30–45% sedangkan kadar C-organik terendah yaitu 1.36% terdapat pada lahan terbuka, kemiringan 30-45%. Nilai pH tanah di lokasi penelitian termasuk sangat masam sampai agak masam (3.4 – 5.69), nilai KTK tanah sangat rendah sampai rendah (3.81 me/100 g –16.4 me/100 g). Hasil uji korelasi menunjukkan bahwa tipe penggunaan lahan memiliki korelasi kuat dengan C-organik tanah dengan nilai konstanta korelasi 0.729 . Selanjutnya, dengan menggunakan analisis regresi berganda diperoleh hasil bahwa tipe penggunaan lahan dan lereng memiliki keterkaitan dengan kandungan C organik tanah dengan nilai konstanta masing-masing adalah 0.119 dan 0.015., Agricultural land used continuously can reduce soil fertility. One of the indicators of soil fertility is soil organic matter. Organic matter content is measured by analyzing the soil organic-C content. The objective of this study was to determine the distribution of soil organic-C content in PT. Perkebunan Buah Subang and the factors that affect it, including environmental conditions and soil characteristics. Soil sampling was carried out in a composite with notice the differences in slope and land use types. The results showed that the highest organic- C content was 3.13% in bamboo forest land use, a slope of 30-45%, while the lowest organic-C content was 1.36% in bare land, a slope of 30-45%. Soil pH values at the research location were very acid to slightly acid (3.4 - 5.69), the soil cation exchange capacity values were very low to low (3.81 me/100 g – 16.4 me /100 g). The correlation test showed that the land use type had a strong correlation with soil organic-C, with a constant correlation value of 0.729. Furthermore, using multiple regression analysis, the result is that the land use type and slope were related to soil organic-C content with constant values of 0.119 and 0.015.
Keyword: correlation test, organic-C, multiple regression test, land use type

Judul: Analysis Biological and Chemical Characteristics of Soil in Several Types Land Use in Bogor Regency
Abstrak: Penggunaan lahan di Kabupaten Bogor memiliki vegetasi beragam dan karakteristik tanah berbeda. Karakteristik tanah memiliki pengaruh terhadap pengelolaan lahan. Keberadaan mikrob tanah dapat digunakan sebagai bioindikator kesuburan tanah. Kesuburan tanah dihasilkan oleh interaksi sifat fisik, kimia, dan biologi tanah. Penelitian ini bertujuan mengetahui karakteristik sifat biologi dan kimia tanah pada berbagai tipe penggunaan lahan di Kabupaten Bogor. Pengambilan sampel tanah dilakukan dengan menggunakan metode purposive random sampling dengan 5 kali ulangan. Lokasi penelitian meliputi delapan penggunaan lahan yaitu kebun bambu, kebun jabon, kebun sengon, kebun lamtorogung, tegalan, tanaman sereh wangi, kebun buah naga, dan kebun pisang. Hasil analisis menunjukkan lahan pisang dan buah naga memiliki kadar C-organik, N-total tertinggi dan populasi fungi tertinggi yaitu 3,78 x 105 CFU/gram. Sedangkan pada lahan di Kecamatan Jasinga yang memiliki hara dan populasi fungi yang cukup dan populasi Azotobacter tertinggi yaitu pada lahan lamtorogung dapat diusahakan untuk tanaman perkebunan yang lebih memiliki nilai jual lebih tinggi seperti pada lahan tegalan dapat ditanami pohon karet, kelapa sawit, atau kakao., Land use in Bogor Regency has diverse vegetation and different soil characteristics. Soil characteristics have an influence on land management. The presence of soil microbes can be used as bioindicators of soil fertility. Soil fertility is produced by the interaction of physical, chemical, and biological properties of the soil. This study aims to determine the characteristics of the biological and chemical properties of soil in various types of land use in Bogor Regency. Soil sampling using the purposive random sampling method with 5 repeats. The research location includes eight land uses, namely bamboo, jabon, sengon, lamtorogung gardens, moorings, fragrant lemongrass plants, dragon fruit orchards, and banana gardens. The results of the analysis showed that banana and dragon fruit fields had the highest C-organic, N-total levels and the highest fungi population of 3,78 x 105 CFU/gram. Meanwhile, on land in Jasinga District which has sufficient nutrients and fungi populations and the highest Azotobacter population, namely on lamtorogung land, it can be cultivated for plantation crops that have a higher selling value, such as in moorlands that can be planted with rubber trees, oil palm, or cocoa.
Keyword: Azotobacter sp., microbes, soil fertility, total fungi

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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