Judul: Pengaruh Bahan Organik terhadap Eh dan pH, serta Korelasinya terhadap P pada Tanah yang Digenangi
Abstrak: Prolong P fertilization in intensive rice cultivation have been resulted in unavailable-residual P accumulation in the soil. Further P fertilization in such soil does not have significant effect in increasing rice productivity. Submerged ricefield is predominated by reduced condition. In order to increase the accumulated unavailable-residual P, application of organic matter as source of electron donor was studied. This research was aimed to study the effects of organic matter on Eh and pH and their correlationswith to P-availability in a submerged soil. Organic matter treatments were 0, 500, 750, 1000,2000, 5000, 10000, 20000, and 40000 kg/ha. Experimental unit was 200 g soil (105°C oven dry-weight) in a 10 cm (diameter) pot. The soil was submerged for 7 weeks, and the soil’spH, Eh, and available P were measured periodically. The available P measured included NaHCO3-P (fastly available P) and NaOH-P (slowly available P). The results in general showed that the Eh decreased, while the pH increased along withincreasing quantity of organic matter, and with submerging time. There were significant negative correlations between Eh and pH (r = 0,840**), between Eh and fastly available P (r = -0,613**), and between Eh and total available P (r = -0,561**). However, there was no significant correlation between Eh and slowly available P (r = 0,0028). Furthermore, there were no significant correlations between pH (at range of 6,3±0,2) with all forms of available P.
Keyword: Bogor Agricultural University (IPB), Submerging Time, pH, Organic Matter, Eh, Available P

Judul: Perubahan Fraksi Fosfor Cepat Tersedia pada Tanah Tergenang yang Diameliorasi Bahan Organik
Abstrak: Prolong phosphorus fertilization has result in high unavailable P residue in soil. In this condition, further P fertilization will not result in higher plant productivity known as leveling off. P in soil exists in inorganic and organic forms, and in broad-range of availability from freely available to unavailable forms. The objective of this research was to study the effects of organic matter on rapidly available P extracted with 0.5 M NaHCO3 in submerged soil. Organic matter treatments were 0, 500, 750, 1000, 2000, and 5000 kg/ha. Research unit was 200 g soil (105oC ovendry weight) in a 10 cm diameter pot. Everyweek for 5 weeks, subsamples of each research unit was extracted for determining NaHCO3-P fraction following Tiessen and Moir 1993 procedure. The results showed that NaHCO3-P increased with increasing organic matter treatments and submersion time. Some dynamics, however, were found that likely related to redox dynamics in submerged soil.
Keyword: Bogor Agricultural University (IPB), Submerged Soil, NaHCO3-P, P availability, Organic Matter

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