Judul: Efektivitas Amelioran Abu Vulkanik Merapi dalam Mengubah Sifat Kimia Tanah Ultisol dan Pertumbuhan Kedelai
Abstrak: This research was carried out to study the effect of Merapi volcanic ash in improving chemical properties of Ultisol soil and its influence on the growth and production of soybean. The volcanic ash largely consist of minerals, such as glass volkan, labradorite, augite, bitownite, hiperstine, and hornblende with high total composition elements including Ca, Na, K and Mg that are potential to increase reserves of minerals, enrich chemical composition and physical properties of soil. The volcano ash was given on the Ultisol soil which is infertile. In this work, amelioran volcanic ash was applied at dosage of 0; 2.5; 5; 10; 20; and 40 t/ha. The result showed that the addition of Merapi volcanic ash did not increase the soil pH. However, the higher the dose of the applied volcanic ash the higher the value of Cation Exchange (K, Ca, and Mg) and Cation Exchange Capacity gained. In addition, the volcanic ash can reduce the acidity (Aldd and Hdd) of Ultisol soil. Plant tissue analysis showed that most of the N, P, and K nutrients were present in soybeans, while most of the Ca and Mg were in the leaves with the highest nutrient uptake in a dose of 20 t/ha. Merapi volcanic ash application can increase plant height, leaf number, and soybean yields with the best dose of 20 t/ha.
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Judul: Efektivitas Amelioran Abu Vulkanik Merapi dalam Mengubah Sifat Kimia Tanah Ultisol dan Pertumbuhan Kedelai
Abstrak: Penelitian ini bertujuan mempelajari pengaruh abu vulkanik Merapi pada perubahan sifat kimia tanah Ultisol serta pada pertumbuhan dan produksi kedelai. Kandungan abu vulkanik yang sebagian besar berupa mineral cepat lapuk seperti volkan kaca, labradorit, augit, bitownit, hiperstin, dan hornblende dengan komposisi total unsur tertinggi meliputi Ca, Na, K, dan Mg berpotensi menambah cadangan mineral, memperkaya susunan kimia dan memperbaiki sifat fisik tanah. Abu ini diaplikasikan pada jenis tanah Ultisol yang kurang subur. Pada penelitian ini, amelioran abu vulkanik ditambahkan pada tanah dengan dosis 0; 2.5; 5; 10; 20; dan 40 t/ha. Hasil penelitian menunjukkan bahwa penambahan abu vulkanik Merapi tidak meningkatkan pH tanah. Namun, semakin tinggi dosis abu vulkanik yang ditambahkan, semakin tinggi pula Nilai Tukar Kation (K, Ca, dan Mg) dan Kapasitas Tukar Kation tanah. Selain itu, abu vulkanik dapat menurunkan kemasaman (Aldd dan Hdd) pada tanah Ultisol. Analisis jaringan tanaman menunjukkan bahwa sebagian besar hara N, P, dan K terdapat pada biji kedelai, sedangkan Ca dan Mg sebagian besar terdapat pada daun dengan serapan hara tertinggi pada dosis 20 t/ha. Penambahan abu vulkanik Merapi dapat meningkatkan tinggi tanaman, jumlah daun, dan hasil kedelai dengan dosis terbaik 20 t/ha.
Keyword: Volcanic ash, Ultisol soil, citation  exchange capacity, soybean

Judul: Penggunaan Teorema Homeomorphy 2-Manifold dan Teorema Euler Poincare pada Torus 𝑇�� dan Simplicial Complex 𝐾��
Abstrak: Two dimensional topological spaces are said to be homeomorphic if they have the same topological invariant, where one of topological invariant used is an Euler characteristic. Homeomorphy 2-Manifold’s Theorem and Euler Poincare’s Theorem are used to distinguish two topological spaces. Homeomorphy 2-Manifold’s Theorem uses Euler characteristic to identify two dimensional topological spaces. Euler Poincare’s Theorem is an alternative way to find Euler characteristic with Betti number, which is topological invariant as well. The objective of this paper is to investigate the homeomorphism of torus 𝑇����� and simplicial complex 𝐾�����. Topological space torus and simplicial complex 𝐾����� have the same Euler characteristic, which is two. Based on Homeomorphy 2-Manifold’s Theorem topological space torus 𝑇����� and simplicial complex 𝐾����� is homeomorphic.
Keyword: simplicial, torus, Euler, homeomorphism, topology