Judul: Pengaruh Berbagai Cara Pemberian Bahan Humat serta Efek Residunya pada Produksi Kangkung Darat (Ipomoea reptans Poir.)
Abstrak: Application of humic substances has not been well-implemented in horticultural cultivation. In the other hand, methods on application of humic substances need to be examined due to their solubility in water and little amount required on application. The research was conducted in order to study the effect of various methods of application of humic substances on production of Ipomoea reptans Poir. in several growing seasons and also to describe their mechanism in increasing plant and soil properties. Results show that the application of humic substances carried by zeolite was the best method in increasing plant yields especially at first two planting times. This increasing was supported by stimulation in plant height, number of leaves and length of leaf. After the third planting time, there was no change in soil chemical properties affected by the treatments. The application of humic substances carried by zeolite gave more profit compared to other methods. The mechanism of increasing plant yield by the ameliorants especially resulted by enhancements in rhizosphere i.e. root biomass can uptake nutrients such as N, P, and Fe were better than in other methods.
Keyword: zeolite, residual effect, nutrient content, Ipomoea reptans Poir, humic substances

Judul: Pengaruh Berbagai Cara Pemberian Bahan Humat terhadap Produksi Ubi Jalar (Ipomoea batatas L.)
Abstrak: Utilisation of humic substance has been widely known to have positive effect on plant productivity. Characteristic of this substance that is easily soluble in water and applied in small amount has brought several obstacles on its wide application. Zeolite that has porous structure is a potential mineral used for humic substance carrier. Various studies in order to examine the role of humic substance on crop yield enhancement were reported limitedly on rice and corn so far, whereas it is rarely conducted on sweet potato. Therefore, it is necessary to conduct research for determining the best method of humic substance application on increasing sweet potato yield. In this research, humic substance was applied in several methods i.e. control (without humic substance and zeolite), humic substance applied directly into soil, humic substance sprayed on leaves, zeolite without humic substance, and humic substance carried by zeolite. The results showed that the application of humic substance carried by zeolite was the best method on increasing sweet potato productivity. This improvement on sweet potato yield is shown by the greater amount and bigger size of tubers of each plant. Moreover, the application of humic substance carried by zeolite showed the highest soil exchangeable K.
Keyword: zeolite., sweet potato, production, humic substance

Judul: Metrik Einstein (Anti-) Self-Dual Berdimensi Empat dengan Metode Cartan
Abstrak: Gravitational field equation can be formulated in differential forms (differential geometry), which describes gravity as a manifestation of the curvature of space-time. Curvature of space-time is characterized by a metric that satisfies the gravitational field equation. With differential forms it can be formulated the (anti-) self-dual Einstein equation, which is a modification of the Cartan structure in (anti-) self-dual basis. Calculation of (anti-) self-dual metric with (anti-) self-dual Einstein equation is simpler than the calculation using Christoffel symbols.
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