Judul: Analisis Kinetika Pelepasan Pupuk Urea dalam Hideogel dari Onggok Singkong pada Media Tanah Kering
Abstrak: Efisiensi pemupukan dan kontrol ketersediaan air masih menjadi masalah dalam pertanian. Hidrogel dapat dijadikan solusi, karena mampu menyerap air dan pupuk dan melepaskannya secara lambat. Hidrogel disintesis dari asam akrilat-akrilamida dan onggok singkong yang diikat silang dengan MBA, kemudian dimuati urea dengan variasi 0; 2,5; dan 5% menggunakan teknik dua langkah. Parameter yang diamati meliputi fraksi gel, swelling,kinetika swelling, pemuatan dan pelepasan pupuk pada tanah latosol dan podsolik, kinetika pelepasan pupuk serta karakterisasi morfologi permukaan dan gugus fungsi. Penambahan urea dapat menurunkan kemampuan swelling dan semakin tinggi konsentrasinya, maka semakin banyak urea yang termuat dan terlepas. Hidrogel termuat urea 2,5% dan 5% pada tanah podsolik serta 2,5% pada tanah latosol bersifat slow-release karena persen pelepasannya <15% dalam 24 jam. Kinetika pelepasan urea 2,5% mengikuti model Korsmeyer-Peppas, sedangkan pelepasan urea 5% mengikuti model Higuchi. Morfologi permukaan hidrogel terlihat heterogen dan berpori berukuran 0,6–18, 8 µm, saat termuat urea ada bercak putih yang menutupi pori,dan setelah release pada tanah terlihat adanya ruang kosong. Gugus fungsi hidrogel terdiri atas gugus O-H, C=O, C=C, C-H, C-O, C-C-O dan terdapat gugus C-N saat termuat urea., Fertilization efficiency and control of water availability are still problems in agriculture. Hydrogel can be used as a solution, because it is able to absorb water and fertilizer and release slowly. The hydrogel was synthesized from acrylic acid-acrylamide and cassava waste pulp crosslinked with MBA, then loaded urea with variations 0; 2,5; and 5% used a two-step technique. Parameters observed is gel fraction, swelling, swelling kinetics, fertilizer loading and release on latosol and podzolic soils, fertilizer release kinetics, surface morphology characterization and functional groups. The addition of urea decreases ability of swelling and the higher the concentration, the more urea is loaded and released. The hydrogel contains 2,5% and 5% urea in podzolic soils and 2,5% in latosol soils is slow-release because the release percentage is <15% in 24 hours. The kinetics of 2,5% urea release follow Korsmeyer-Peppas model, while the 5% urea release follows Higuchi. The surface morphology of hydrogel looks heterogeneous and porous measuring 0,6–18, 8 µm μm, when loaded urea there are white patches covering the pore, and after release on the soil there is visible empty space. The hydrogel functional group consists of O-H, C=O, C=C, C-H, C-O, C-C-O groups and C-N group when urea is loaded.
Keyword: hydrogel, fertilizer loading, fertilizer release, soil, urea

Judul: Pengujian Pelepasan Hidrogel Karagenan sebagai Pembawa Pupuk pada Tanah
Abstrak: Hidrogel adalah polimer hidrofilik yang mampu memuat air berkali lipat dari bobot aslinya. Hidrogel disintesis menggunakan karagenan, asam akrilat dan akrilamida, diikat silang dengan 1% N,N’-metilenbisakrilamida (MBA), serta 16% amonium pesulfat (APS). Hidrogel diuji dan dianalisis nilai swelling, kinetika swelling, fraksi gel, kapasitas adsorpsi, pemuatan pupuk, pelepasan pupuk, analisis gugus fungsi, serta morfologi permukaan hidrogel. Nilai swelling pada hidrogel dengan variasi pupuk urea 0%, 5% dan 10% dipengaruhi oleh kapasitas adsorpsi dan konstentrasi urea sehingga variasi urea 5% memiliki nilai swelling terbaik dan mampu memuat pupuk sebanyak 2273,5 mg/L (54,507%). Pelepasan pupuk urea 5% dan 10% diuji pada tanah pasirdan tanah andosol dipengaruhi oleh nilai swelling dan variasi tanah. Hidrogel pupuk 10% pada tanah pasir merupakan pelepasan pupuk paling lambat. Hidrogel pupuk 5% dan 10% termasuk ke dalam pupuk lepas lambat. Pelepasan pupuk yang lambat memiliki pori hidrogel yang kecil, serta memiliki nilai swelling dan kapasitas adsorpsi tidak terlalu tinggi., Hydrogel is a hydrophilic polymer that can contain water many times its original weight. The hydrogel was synthesized using carrageenan, acrylic acid and acrylamide, cross-linked with 1% N,N’-methylenebisacrylamide (MBA), and 16% ammonium pesulfate (APS). The hydrogel was tested and analyzed for swelling value, swelling kinetics, gel fraction, adsorption capacity, fertilizer loading, fertilizer release, functional group analysis, and hydrogel surface morphology. The swelling value of the hydrogel with variations of 0%, 5% and 10% urea fertilizer is influenced by the adsorption capacity and urea concentration so that the 5% urea variation has the best swelling value and is able to contain fertilizer as much as 2273.5 mg/L (54.507%). The release of 5% and 10% urea fertilizer tested on sandy soil and Andosol soil was influenced by swelling values and soil variations. 10% fertilizer hydrogel in sandy soil is the slowest release of fertilizer. 5% and 10% fertilizer hydrogels are included in slow release fertilizers. Slow releasing fertilizer has small hydrogel pores, and has a swelling value and not too high adsorption capacity.
Keyword: carrageenan, fertilizer release, hydrogel, soil

Judul: Construction of Strongly Optimal Binary Linear Code with Minimum Distance 9 and 11
Abstrak: A binary linear code of length n over q F is a subspace of n q F . A code has three parameters that attached to it, namely length, dimension, and minimum distance. A code with length n, dimension k and minimum distance d is often called [n, k, d ]-code. Usually, when two parameters are given, then we want to find a code that has the best value for the last parameter. Based on Gilbert- Varshamov bound, if a [n, k, d ]-code exists and can not be expanded, we call it a strongly optimal code. In this paper, we construct strongly optimal code with minimum distance 9 and 11. In constructing the code, we created a theorem and algorithm based on Gilbert-Varshamov bound before we implement the algorithm to MAPLE programming language. Because of computational limitations, the program can only construct up to k = 10 for d = 9 and k = 12 for d = 11.
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