Judul: Comparison of Leached Nitrogen in Four Types of Urea
Abstrak: Penggunaan pupuk urea yang tidak tepat menyebabkan rendahnya efisiensi nitrogen oleh tanaman. Modifikasi kimia molekul urea dengan senyawa formaldehid dapat dilakukan untuk mengontrol pelepasan NH4+ dan NO3− dari urea. Uji inkubasi dan pencucian tanah dilakukan untuk mengetahui kelarutan N urea termodifikasi formaldehid (urea granular dan prill), dan urea konvensional (urea kujang dan urea pusri) sebagai perlakuan pembanding. Campuran Latosol dan pasir kuarsa dengan perbandingan (1:1) diinkubasi, kemudian dicuci pada hari ke 7, 14, 28, 45, 60 dan 90 dengan melewatkan air di kolom tanah. Hasil pengujian menunjukkan bahwa transformasi urea dalam tanah dimulai dari pelarutan menjadi NH4+, kemudian teroksidasi menjadi NO3-. Proses tersebut berlaku sama untuk semua jenis urea yang diuji. Urea yang dimodifikasi formaldehid melepaskan nitrogen dalam periode waktu yang lebih lama daripada urea konvensional. Kadar formaldehid mempengaruhi laju pelepasan N. Urea granular (0,5% formaldehid) menghasilkan N tercuci lebih rendah daripada urea prill (0,1% formaldehid) tetapi tidak berbeda nyata. Kadar N-NO3- tecuci kumulatif dari urea granular dan urea prill tidak berbeda dengan urea konvensional. Urea granul memiliki kandungan N-NH4+ tercuci kumulatif yang jauh lebih rendah daripada urea konvensional. Sedangkan kadar N-NH4+ tercuci kumulatif pada perlakuan urea prill tidak berbeda nyata dengan perlakuan urea konvensional (Kujang dan Pusri urea)., Improper use of urea fertilizer causes low nitrogen efficiency by plants. Chemicalmodification of urea molecules with formaldehyde compounds can be carried out to control the release of NH4+ and NO − from urea. Incubation and soil washing tests were carried out to determine the solubility of formaldehydemodified N urea (granular and prill urea), and conventional urea (kujang urea and pusri urea) as comparison treatments.The mixture of latosol and quartz sand in the ratio (1:1) was incubated, then washed on days 7, 14, 28, 45, 60 and 90 by passing water in the soil column. The test results show that the transformation of urea in the soil starts from dissolving into NH4+, then oxidizes to NO3-. The process applies equally to all types of urea tested. Formaldehyde-modified urea releases nitrogen over a longer period of time than conventional urea. The level of formaldehyde affects the rate of N release. Granular urea (0.5% formaldehyde) produceslower leached N than prill urea (0.1% formaldehyde) but not significantly different. Thecumulative leached N-NO3- levels of granular urea and prill urea were not different fromthat of conventional urea. Granulated urea has a significantly lower cumulative leached N-NH4+ content than conventional urea. Meanwhile, the cumulative levels of N-NH4+ leachated in the prill urea treatment were not significantly different from the conventional urea treatment (Kujang and Pusri urea).
Keyword: formaldehid, inkubasi, nitrogen, pencucian, urea

Judul: Comparison of nitrogen absorption by corn (Zea mays L.) from four urea fertilizers
Abstrak: Jagung merupakan salah satu komoditas pangan utama di Indonesia. Peningkatan produktivitas jagung umumnya menggunakan pupuk urea untuk memenuhi kebutuhan nitrogennya. Masalah utama terkait penggunaan urea yaitu tingginya jumlah nitrogen tercuci. Salah satu upaya mencegah pencucian N yaitu dengan mengubah senyawa urea menjadi senyawa urea lambat tersedia (slow release), diantaranya dengan mengubah sebagian senyawa urea menjadi urea-formaldehida yang bersifat lambat tersedia. Penelitian ini bertujuan untuk mempelajari pengaruh empat jenis pupuk urea terhadap bobot biomassa kering, serapan nitrogen, dan efisiensi serapan nitrogen. Penelitian menggunakan rancangan acak lengkap satu perlakuan dengan empat ulangan. Penelitian dilaksanakan di rumah kaca dengan media tanah seberat 15 kg (Bobot Kering Mutlak) dengan polybag. Perlakuan terdiri atas perlakuan tanpa pemupukan N (kontrol), pemupukan urea konvensional yang terdiri dari urea kujang dan urea pusri dan urea slow-release berupa urea urea granul (0,5% formaldehida) dan urea prill (0,1% formaldehida). Biomassa bagian atas tanaman untuk keperluan analisis dipanen tiap minggu selama 10 minggu dari satuan percobaan yang terpisah. Analisis kadar N jaringan jagung dilakukan setiap minggu panen dengan metode mikro Kjehdahl. Hasil percobaan menunjukkan pemberian urea slow-release, khususnya urea granul, meningkatkan bobot biomassa jagung dibandingkan dengan penggunaan urea konvensional. Selain itu, penggunaan urea slow-release memiliki tingkat efisiensi lebih tinggi dibandingkan dengan urea konvensional. Faktor yang menyebabkan urea granul memiliki serapan dan efisiensi yang lebih tinggi adalah pelapisan butir dengan senyawa urea-formaldehid pada urea slow-release., Corn is one of the main foods commodities in Indonesia. To increase corn productivity, urea fertilizer is commonly used to supply its nitrogen (N) needs. The main problem related to the use of urea fertilizer is the high amount of nitrogen leached. One way to prevent nitrogen leaching is by forming a urea compound to a slow-release compound, one of them is changing part of the urea compound to urea-formaldehyde. This research was aimed to study the effect of four different urea fertilizers on corn’s biomass production, nitrogen absorption, and nitrogen absorption efficiency. This research used a completely randomized design of one factor with four repetitions. The research was carried out in a greenhouse with 15 kg soil as plant’s media in a polybag. The treatments consisted of treatment without N fertilization (control), conventional urea fertilizers (kujang urea and pusri urea), and slow-release ureas which is granule urea (0.5% formaldehyde) and prill urea (0.1% formaldehyde). Upper plant biomass for analysis was harvested every week for 10 weeks from separated experimental uni. Total N analysis was determined by mikro Kjeldahl method. The result showed that the application of slow-release urea, especially granulated urea, increased nitrogen absorption and biomass weight compared to the application of conventional urea fertilizers. Factors that cause the granule slow-release urea has higher absorption and efficiency is the coating of the grain with urea-formaldehyde
Keyword: conventional urea, granulated urea, nitrogen efficiency, slow-release, urea-formaldehyde

Judul: Penentuan Nilai Eigen dan Vektor Eigen dari Matriks Tridiagonal 2-Toeplitz dengan Pendekatan Polinomial Chebyshev
Abstrak: The eigenvalues and eigenvectors of a matrix can be determined by finding its characteristic polynomials. The characteristic polynomials of a tridiagonal 2-Toeplitz matrix is shown to be closely connected to polynomials which satisfy the Chebyshev recurrence relationship. If the order of the matrix is odd, then the eigenvalues are found explicitly in terms of the Chebyshev zeros and the eigenvectors are found in terms of the polynomials satisfying the recurrence relationship. For even ordered matrices, the situation is more complicated. The problem in these cases is that although the Chebyshev recurrence formula is still applied, its initial values are not generating Chebyshev polynomials
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