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: Pengaruh pemberian bahan humat, fosfor dan waktu inkubasi terhadap ketersediaan fosfor pada tanah latosol dan podsolik
Abstrak: Salah satu permasalahan tanah masam adalah tingginya fiksasi fosfor yang mengakibatkan turunnya kadar P tersedia dalam tanah, fiksasi fosfor ini dapat diturunkan dengan ditambahkannya bahan organik. Tujuan dari penelitian ini adalah untuk mengetahui pengaruh pemberian bahan humat, larutan P dan waktu inkubasi terhadap ketersediaan fosfor pada Latosol dan Podsolik Dramaga. Penelitian dilakukan dengan penambahan bahan humat dengan dosis 0 ppm/200g tanah (D0), 25 ppm/ 200g tanah (D1) dan 50 ppm/200g tanah (D2). Larutan P dengan dosis 0 ppm/ 200g tanah (P0) dan 25 ppm/200g tanah (P1). Adapun waktu inkubasi 0 minggu (T0), 3 minggu (T3) dan 6 minggu (T6). Hasil penelitian menunjukkan terjadinya peningkatan P-tersedia setelah perlakuan pemberian bahan humat. Perlakuan D1 dan D2 secara nyata mampu meningkatkan P-tersedia pada Latosol sebesar 4.98 ppm dan 17.7 ppm, dan Podsolik sebesar 5.92 ppm dan 16.96 ppm. Kombinasi bahan humat, larutan P dan waktu inkubasi mampu meningkatkan pH secara nyata pada Latosol. Kombinasi bahan humat dan waktu inkubasi secara nyata meningkatakan pH pada Podsolik. Kombinasi larutan P dan waktu inkubasi secara nyata menurunkan Al-dd. Secara umum perlakuan terbaik untuk meningkatkan P-tersedia, pH dan menurunkan Al-dd yaitu D2P0T6.
Keyword: Bogor Agricultural University (IPB), waktu inkubasi., Podsolik Dramaga, Latosol Dramaga, fosfor, bahan humat

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