Judul: Pengujian metode uji cepat penetapan kadar C-Organik
Abstrak: Before being introduced for wide application, the reliability of quick test method for soil organic carbon content has to be evaluated. The objective of this experiment was to evaluate quick test method for determining soil organic carbon content developed by Indonesian Soil Research Institute. In this research the effect of soil sample preparation (comparison between prepared soil sample and unprepared/direct soil sample) and the effect of kinds of reagent (IA or IB) were evaluated. For this purpose, froth height data of quick test of soil organic carbon was correlated with organic carbon content of Walkley and Black method. In addition, the best time for froth height observation was determined in this research. Calibration of froth height was conducted on organic carbon content of Walkley and Black method (%) for categorizing froth height into classes of low, médium, and high. Research results indicated that the quick test method was better to be applied on direct soil samples (without air drying, crushing, and sieving), both for reagents IA and IB. Reagent IA was better than reagent IB, and both kinds of reagent were better for analyzing organic carbon content of paddy soil.
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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: Invers Drazin dari Matriks Toeplitz Singular
Abstrak: Matriks Toeplitz adalah matriks yang setiap unsur pada diagonal utama bernilai sama dan setiap unsur pada subdiagonal yang bersesuaian dengan diagonal utama juga bernilai sama. Matriks singular adalah matriks yang tidak bisa ditentukan inversnya. Akan tetapi, dapat diupayakan untuk ditentukan inversnya menggunakan invers matriks yang diperumum. Invers Drazin merupakan salah satu jenis invers matriks yang diperumum. Pada karya ilmiah ini ditentukan invers Drazin dari matriks Toeplitz singular dengan menggunakan metode Leverrier Faddeev. Kemudian, ditentukan invers Drazin dari matriks Toeplitz singular yang direpresentasikan sebagai penjumlahan segitiga bawah dan segitiga atas matriks Toeplitz berdasar pada teorema Gohberg dan Semencul., Toeplitz matrix is a matrix in with element on the main diagonal has the same value and on the subdiagonal corresponding to the main diagonal also has the same value. Singular matrix is a matrix that has no inverse. However, it can be attempted to determine the inverse using a generalized inverse matrix. Inverse Drazin is a type of generalized matrix inverse. This paper discussed the inverse Drazin for a singular Toeplitz matrix using the Leverrier Faddeev method. Then, the Drazin inverse of the singular Toeplitz matrix which is represented as a sum of products of lower and upper triangular Toeplitz matrix based on Gohberg and Semencul theorem.
Keyword: inverse Drazine, singular Toeplitz matrix