Judul: The Effect of Changes in Soil  Organic Carbon Levels on the Phosphorus Sorption Characteristics in Andisol  Humbang Hasundutan, North Sumatera
Abstrak: Kawasan Humbang Hasundutan Provinsi Sumatera Utara merupakan salah satu daerah pengembangan kawasan lumbung pangan (Food Estate). Jenis tanah pada kawasan ini termasuk Andisol yang memiliki permasalahan pada ketersediaan hara fosfor (P). Andisol merupakan tanah yang berkembang dari bahan vulkanik yang memiliki mineral-mineral klei amorf yang mengerap P sangat tinggi. Penelitian ini bertujuan untuk menganalisis dan mengevaluasi beberapa sifat kimia tanah dan karakteristik erapan P pada Andisol yang belum terganggu dan Andisol yang mendapat penambahan bahan organik sebanyak 20 t ha-1 di Humbang Hasundutan Sumatera Utara. Contoh tanah yang dianalisis adalah berasal dari tiap horizon masing-masing profil tanahnya. Contoh tanah Andisol yang belum terganggu diambil pada kedalaman 0-19 cm dan 19-40 cm, dan contoh tanah Andisol yang sudah diberi bahan organik 20 t ha-1 diambil pada kedalaman 0-17 cm, 17-27 cm, dan 27-50 cm. Hasil penelitian menunjukkan bahwa pemberian bahan organik sebesar 20 t ha-1 meningkatkan kadar karbon (C)- Organik, P-tersedia, dan pH, serta menurunkan aluminium yang dapat dipertukarkan (Al-dd) pada lapisan atas (kedalaman 0-17 cm dan 17-27 cm). Pemberian bahan organik sebesar 20 t ha-1 tidak berpengaruh secara statistik terhadap erapan P maksimum, tetapi nyata menurunkan konstanta energi erapan P (k) dan standar kebutuhan P (P0.2). Nilai k berkorelasi negatif secara nyata dengan C-Organik. Penelitian ini menunjukkan bahwa pemberian bahan organik 20 t ha-1 meningkatkan kadar C-organik tanah, P-tersedia, pH dan menurunkan nilai Al-dd. Untuk parameter erapan P, pemberian bahan organik tanah 20 t ha-1 menurunkan nilai k dan P0.2 dimana nilai k berkorelasi negatif dengan kadar C-organik tanah. Semakin tinggi kadar C organik tanah maka semakin rendah nilai k erapan P sebagai konstanta energi ikatan erapan P., Humbang Hasundutan area of North Sumatera Province is one of the development areas for the food estate area. Soil types in this area was Andisol which have problem with phosphorus (P) availability. Andisol is a soil that develops from volcanic material that has amorphous clay minerals that sorbs very high P. This study aimed to analyze and evaluate some soil chemical properties and P sorption characteristics in Andisol that has not been disturbed and Andisol which received the addition of organic matter as much as 20 t ha-1 in Humbang Hasundutan North Sumatra. The soil samples analyzed were derived from each horizon of each soil profile. Undisturbed Andisol soil samples were collected at a depth of 0-19 cm and 19-40 cm, and Andisol soil samples that have been applied with organic matter 20 t ha-1 collected at a depth of 0-17 cm, 1 7-27 cm, and 27-50 cm.The results showed that soil samples which was applied with organic matter increased organic carbon (C) levels, available P, soil pH, and lower exchangeable aluminium (exch Al) at the depth of 0-17 cm and 17-27 cm. The application of 20 t ha-1 did not statistically affect the P sorption maximum but significantly decreased the P bonding energy constant (k) and standard P requirement (P0.2) . The k value significantly negatively correlated with organic C. This study suggested that the application of organic matter 20 t ha-1 increased soil organic C levels, available P, soil pH and lower
Keyword: correlation, organic matter, bonding energy, soil organic C

Judul: Pengaruh Bahan Organik terhadap Ketersediaan Fosfor pada Tanah-Tanah Kaya Al dan Fe
Abstrak: Phosphorus (P) is one of the essential nutrients for plants. However, the availability of P that can be absorbed by plants in the soil is generally very low, because P in the soil are manily in adsorbed form. Addition of organic matter can improve the availability of P in the soil, because organic acids that are resulted by decomposition of organic matter have an ability to make chelation of Al and Fe so P may become available. The aim of this research was to study effect of organic matter in releasing and preventing adsorption of P and to study wether the effect of organic matter is better if it is applied before or after P fertilization. This research consisted of five treatments: (1) Soil (Andosol, Latosol, Podsolic) was added with straw compost and 2 weeks later P fertilizer was added, (2) Soil (Andosol, Latosol, Podsolic) was added with P fertilizer and after 2 weeks straw compost was added, (3) Soil (Andosol, Latosol, Podsolic) was added with cow manure compost and after 2 weeks P fertilizer was added, (4) Soil (Andosol, Latosol, Podsolic) was added with P fertilizer and after 2 weeks cow manure compost was added, and (5 ) Soil (Andosol, Latosol, Podsolic) was added with P fertilizer only. Each treatment on the three soils was incubated for 1 and 2 months. The results showed that treatment of organic matter and P fertilizer addition is more effective in increasing pH and P-availability, as well as lowering the Al-dd and Fe-availability on the three soils than the treatment of only addition of P fertilizer. Cow manure compost gives a higher effect than straw compost. The addition of organic matter to improve releasing adsorbtion of P and preventing adsorption of P on Latosol and Podsolic, meanwhile for Andosol effect of organic matter is less visible. Latosol and Podsolic, the addition of organic matter is better if it is done after P fertilization, meanwhile for Andosol the addition of organic matter is better if it is done before P fertilization. The highest available-P of Andosol is in the treatment is soil was added with cow manure compost and after 2 weeks P fertilizer was added is 10.67 ppm, meanwhile available-P for Latosol is soil was added with P fertilizer and after 2 weeks cow manure compost was added is 90.95 ppm, and Podsolic is Soil was added with P fertilizer and after 2 weeks cow manure compost was added is 40.73 ppm.
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Judul: Closed Knight’s Tour pada Papan Catur Berbentuk Persegi Panjang dengan Ukuran Maksimal 8 × 8
Abstrak: Closed Knight’s Tour merupakan langkah kuda yang mengunjungi setiap kotak pada papan catur tepat satu kali dengan langkah kuda berawal dan berakhir pada kotak yang sama. Graf yang terbentuk dari closed knight’s tour dinotasikan sebagai graf G(m,n), dengan m adalah banyaknya baris dan n adalah banyaknya kolom. Graf tersebut memuat Hamiltonian cycle. Sebuah graf terhubung G adalah graf bipartite jika dan hanya jika graf tersebut tidak memiliki cycle dengan panjang ganjil. Papan catur yang memenuhi syarat cukup untuk memiliki closed knight’s tour adalah papan catur berukuran 5 × 6, 5 × 8, 6 × 6, 6 × 7, 6 × 8, 7 × 8, dan 8 × 8.
Keyword: bipartite, closed knight’s tour, hamiltonian cycle, knight’s tour, teori graf