Judul: Soil Chemical Properties and Phosphorus Sorption  Characteristic on Agroforestry Based-Pepper Land and Cassava Land in North  Lampung
Abstrak: Perubahan penggunaan lahan dari agroforestri lada menjadi perkebunan singkong terjadi secara masif di Lampung Utara karena rendahnya harga lada di pasaran. Penelitian ini bertujuan mengevaluasi perubahan sifat kimia tanah dan karakteristik erapan fosfor (P) akibat perubahan penggunaan lahan tersebut. Beberapa sifat kimia tanah dan karakteristik erapan P dianalisis pada contoh tanah lahan agroforestri lada serta lahan singkong berusia 1 tahun dan 15 tahun. Data percobaan erapan P disimulasikan menggunakan persamaan Langmuir. Hasil penelitian menunjukkan perubahan penggunaan lahan secara nyata menurunkan pH, karbon (C)-organik tanah, kation-kation basa, serta kapasitas tukar kation dan meningkatkan aluminium yang dapat ditukar. Perubahan penggunaan lahan tidak mempengaruhi secara statistik terhadap erapan maksimum P, tetapi mempengaruhi konstanta energi ikatan P (K) dan kebutuhan P standar (P0,2). Nilai K dan P0,2 perkebunan singkong secara signifikan lebih tinggi dibandingkan agroforestri lada kedalaman 0-20 cm. Perubahan penggunaan lahan secara signifikan mempengaruhi pelepasan P. Persentase P yang dilepaskan pada lahan singkong berusia 15 tahun signifikan lebih rendah dibandingkan lahan agroforestri lada. Nilai K berkorelasi negatif dengan C-organik tanah dimana penurunan C-organik tanah meningkatkan nilai K dalam erapan P dan dalam proses pelepasan P. Perubahan penggunaan lahan ini menyebabkan beberapa sifat kimia tanah menjadi lebih buruk dan meningkatkan nilai K erapan P., The land use change from agroforestry based-Pepper to cassava plantations occurs massively in North Lampung due to the low price of pepper in the market. This study aimed to evaluate the changes in soil chemical properties and phosphorus (P) sorption characteristics in those lands. Some soil chemical properties and P sorption characteristics were analyzed in soil samples of agroforestry based-pepper land and 1-year-old also 15-year-old cassava land. The data of P sorption was simulated by Langmuir equation. The results showed land use change decreased significantly pH, soil carbon (C)-organic, basic cations, cations exchange capacity and increased exchangeable aluminum. The P sorption maximum did not affect statistically, but affected of the P bonding energy (K) and standard P requirement (P0,2). K and P0,2 value of cassava plantations were significantly higher than pepper agroforestry at 0-20 cm soil depth. The land use change also significantly affected the P release. Percentage of P released on 15-years-old cassava plantation was lower than agroforestry-based pepper. K value was negatively correlated with the soil C organic. Decreasing of soil C-organic increased K value in the P sorption and P release process. The land use change caused some chemical properties worse and increased the K value of P sorption.
Keyword: Phosphorus bonding energy, phosphorus desorption, soil C-organic

Judul: Perbaikan Sifat Kimia Tanah Masam, Produksi, dan Serapan P Tanaman Kacang Tanah (Arachis hypogaea) dengan Pemberian Pupuk Fosfat Alam
Abstrak: Potential of land resources in Indonesia is very large. Indonesia has 148 million ha of upland. Climate variation, specifically precipitation in most areas of Indonesia is relatively high therefore leaching of bases in the soil mostly high. It causes the low content of bases in soil, and then the soil become acid and have nutrients deficiency. About 102.8 million ha or 69.5 % of the total upland in Indonesia have acid soil. The utilization of acid soil for agriculture have several problems such as P-deficiency. It is due to the phosphate ions is adsorbed by the various component in the soil, such as Fe and Al ions, and Fe and or Al hydrous oxide. One of the efforts to overcome the P-deficiency is to apply rock phosphate into acid soil. The use of rock phosphate as fertilizer because highly soluble in the acid soil condition. Therefore, rock phosphate is appropriate as a source of P fertilizer in acid soil. The objectives of this research were to study the effect of rock phosphate fertilizer on the improvement acid soil quality, on groundnut yield, and P uptake of groundnut plant (Arachis hypogaea) in Latosol (Oxyc dytropept) Darmaga, Bogor. The experimental design was used is a randomized complete block design with one factor, that is dosage of phosphate fertilizers. Phosphate Fertilizer used in this experiment were rock phosphate and SP-36. Phosphate fertilizer dosages were: 0% (as a control treatment), Std 100%, Std 50% + P 50%, Std 25% + P 75%, P 100%, P 125%, and P 150%. The results of the study showed that rock phosphate fertilizer significantly increased the soil pH, exchangeable Ca, the uptake of Ca and P of groundnut plant. The phosphate fertilizer treatments were not increase significantly different in the growth, weight of pod, weight of seed, and percentage of full pod. However, the rock phosphate treatments resulted the percentage of full pod (87.76%-90.01%) was higher than standard fertilizer treatment (86.51%).
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Judul: Cycle Hamilton pada Graf Lengkap, Graf Regular, dan Graf 2-Connected 4-Regular Berorder Kurang dari Sepuluh.
Abstrak: Suatu graf disebut graf Hamilton apabila graf tersebut memuat cycle Hamilton, yaitu cycle yang melewati setiap vertex tepat satu kali. Menentukan keberadaan cycle Hamilton pada suatu graf dapat menggunakan syarat cukup yang berupa teorema-teorema yang telah diperkenalkan sejak tahun 1950-an. Beberapa syarat cukup yang dibahas dalam karya ilmiah ini adalah syarat cukup yang berhubungan dengan graf lengkap dan graf regular. ,,,
Keyword: graf Hamilton, graf regular, graf lengkap, graf 2-connected 4-regular.