Judul: Karakterisasi Pelepasan Nitrat pada Andisols di Jawa Barat dan Jawa Tengah
Abstrak: Andisols occupies large area in Indonesia. The area is about 5.4 million hectares. This soil is used extensively by farmers for horticulture, tea plantation and small portion for livestock. The characteristics of nitrate release is very spesific location so that it is necessary to reveal soil properties affecting to the pattern of nitrate release on Andisols in West and Central Java. The experiment of nitrate release was conducted by incubation experiment. The objectives of the research were to (1) characterization of chemical properties of Andisols in West and Central Java, (2) characterization of the pattern of nitrate release on Andisols in West and Central Java, and (3) obtaining correlation between chemical properties and the pattern of nitrate release on Andisols in West and Central Java. Based on soil analyses, the chemical properties of Andisols in West and central Java were different. The release of nitrate on Andisols in Lembang, Pangalengan, Sukamantri and Dieng decreased as the depth of soil samples in the soil profile was deeper and increased as the periode of incubation was longer. Simple correlation test showed that the potential nitrate release (N0) positively correlated with total carbon (r=0.08), total nitrogen (r=0.14), oxalate-extractable iron (Feo) (r=0.05), dithionite-citrate-bicarbonate-extractable aluminum (Ald) (r=0.07) and dithionite-citrate-bicarbonate-extractable iron (Fed) (r=0.39). The N0 negatively correlated with oxalate-extractable aluminum (Alo) (r=-0.08) and Alo + ½ Feo (r=-0.07). As for the rate constant (k), k only positively correlated with Fed (r=0.04).
Keyword: soil chemical properties, nitrate release, andisols

Judul: Mineralization potency of N-NH4 + and N-NO3 - at Andisol Soil planted vegetables on highly upland.
Abstrak: Nitrogen is one of essential minerals for plant but it has less availability in the soil. Nitrogen is absorbed by plant as NH4 + (ammonium) and NO3 - (nitrate). Nitrogen organic in the soil is easy to change so this experiment was carried out to measure mineralization potency of N-NH4 + and N-NO3 - at Andisol Soil planted vegetables on highly upland. Andisol soils sample used came from Kejajar Wonosobo and Sumowono Semarang represent farmer 1 and 2. The first step of analysis was preparation of soil sample, and put it into PVC (diameter 5,4 cm and high 10 cm) for incubation. Experiment needed 102 days incubation with 9 times sampling with time duration of each sampling is 0, 7, 18, 31, 46, 60, 74, 88, and 102 days. Then, NH4 + and NO3 - contents of the soil were analyzed using KCl and CaCl2 spectrofotometri method. Based on the experiment, mineralization potency of released N-NH4 + at Kejajar Wonosobo from soil farmer 1 and 2 were 7,45 and 7,15 mg kg-1, whereas N-NO3 - of farmer 1 and 2 were 111,20 and 123,41 mg kg-1, respectively. Mineralization potency of released N-NH4 + at Sumowono Semarang from soil farmer 1 and 2 were 7,23 and 7,17 mg kg-1, whereas N-NO3 - of farmer 1 and 2 were 94,95 and 103, 55 mg kg-1, respectively. Ammonium or Nitrate mineralization processes almost has same pattern in andisol soils at Kejajar Wonosobo and Sumowono Semarang.
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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. Suatu graf lengkap berorder 𝑛������ ≥ 3 dan graf r-regular berorder 𝑛������ ≤ 2𝑟������ + 1 merupakan graf Hamilton, Karena kedua graf tersebut memuat cycle Hamilton. Selanjutnya, syarat cukup tersebut digunakan untuk menentukan keberadaan cycle Hamilton pada graf 2-connected 4- regular berorder kurang dari 10.
Keyword: graf Hamilton, graf regular, graf lengkap, graf 2-connected 4-regular