Judul: Pengaruh Pemberian Abu Volkanik Gunung Kelud Letusan Tahun 2014 terhadap Produksi dan Efisiensi Pemupukan Kedelai.
Abstrak: Indonesia has many volcanoes that their material eruption causing rejuvenation of soil forming process and renew long term soil fertility. One of volcanoes in Indonesia is Kelud Mountain*. This research is to investigate the effect of Kelud Mt. volcanic ash application on soybean growth and yield efficiency. The pot experiment was carried out in poor-very acid Inceptisol soil. The ash was dominated by fine size particles (<100 μm). Based on total chemical analysis, Kelud volcanic ash was intermediet material in composition that consisted of SiO2, Al2O3, CaO, Fe2O3, Na2O, MgO, K2O, TiO2, SO3, P2O5, MnO, SrO, ZrO2, Cr2O3, ZnO and CuO. The field experiment conducted in randomize factorial block design with combination of four doses of volcanic ash (0, 10, 20, and 30% of w/w), and three doses of fertilizers (0, 50, and 100% of NPK recommendation doses), in five replication. The result showed that fertilizer application was not significant effect to all variables. In other side, Kelud volcanic ash addition had significant effect to nutrients uptake of P, K, and Ca, and was very significant effect to upper bio mass, amount of pods, pods weight, yield, and nutrient uptake of N and Mg. The treatment that was the highest effect was of application 30% volcano ash of doses treatment. Higher volcanic ash rates higher P and K fertilizer efficiency.
Keyword: volcanic ash, Kelud Mt, soybean, fertilizer efficiency, Inceptisol

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