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: 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: Invers dari Matriks Tridiagonal Jacobi
Abstrak: Suatu matriks berukuran n×n dinamakan matriks tridiagonal jika untuk . Karya ilmiah ini memberikan algoritma yang mudah untuk menemukan invers ( dari matriks tridiagonal Jacobi yang simetrik dan nonsimetrik. Setiap elemen pada matriks tridiagonal ini adalah bilangan real. Terdapat 3 lema dan 2 teorema untuk menentukan . Lema pertama menunjukkan persamaan utama dalam membuktikan lema-lema dan teorema-teorema selanjutnya. Invers dari matriks yang simetrik dibuktikan oleh lema kedua yang menunjukkan elemen-elemen baris ke- dari . Selanjutnya, lema kedua dilengkapi dengan teorema pertama yang menunjukkan elemen-elemen dengan . Invers dari matriks yang nonsimetrik dibuktikan oleh lema ketiga yang menunjukkan elemen-elemen dengan dan elemen-elemen dengan dibuktikankan oleh teorema kedua.
Keyword: symmetric, nonsymmetric, matrix