Judul: Pemuatan dan Pelepasan Pupuk Urea pada Hidrogel Asam Akrilat-Akrilamida Berbasis Onggok Singkong
Abstrak: Proses pemupukan pada tanaman yang kurang efektif akan menurunkan produktivitas tanaman. Pemuatan pupuk pada hidrogel dapat dijadikan sebagai salah satu solusi untuk mengontrol proses pemupukan yang lebih efektif. Hidrogel disintesis dari onggok dan polimer asam akrilat akrilamida menggunakan metode ikat silang kimia. Selanjutnya, hidrogel dimuati urea dengan variasi konsentrasi 0%, 3%, 5%, 7%, dan 9% menggunakan metode teknik dua langkah. Hasil penelitian menunjukkan bahwa penambahan urea pada proses perendaman hidrogel mampu meningkatkan kemampuan swelling dan kekerasan hidrogel, serta menurunkan nilai kelengketan hidrogel. Selain itu, peningkatan konsentrasi urea juga berpengaruh pada proses pelepasan pupuk. Semakin tinggi konsentrasi urea, semakin rendah persentase pelepasan pupuk yang diperoleh. Proses pelepasan urea pada penelitian ini cenderung terjadi secara cepat pada awal pengukuran dan lepas secara perlahan setelah 24 jam pengukuran., The fertilization process on plants that are less effective will reduce plant productivity. The addition of fertilizer to the hydrogel can be used as a solution to control the fertilization process more effectively. The hydrogel was synthesized from cassava and acrylic acid polymer acrylamide using the chemical crosslinking method. Furthermore, the hydrogel was loaded urea with variations in concentrations of 0%, 3%, 5%, 7%, and 9%. The loading of urea fertilizer on the hydrogel was carried out by a two-step technique. The results showed that the addition of urea in the hydrogel immersion process was able to increase the swelling ability and hydrogel hardness, as well as reduce the hydrogel adhesiveness value. In addition, the increase in urea concentration also affects the process of releasing fertilizer. The higher the concentration of urea fertilizer, the lower the percentage of fertilizer released. The process of releasing urea in this study tends to occur quickly at the beginning of the measurement and slowly after 24 hours of measurement.
Keyword: hydrogel, fertilizer loading, fertilizer release, urea

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: Centrality test for Non-Normal And Skewed Population
Abstrak: The t modified 2 test is more robust than t test for skewed popnlation. This test tolerate the population skewness from -1.2 to 1.2 sample size is reather than 25. The sign test robust to the populated skewed population, but the value of the estimated always close to the size of the tcst. Wilcoxon test is not robust to the population skewness. This test is more suittalble for Symmetric population
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