Judul: Kompetisi paspalum conjugatum berg, dengan kacang tanah pada beberapa status nitrogen tanah
Abstrak: Pertumbuhan gulma di antara tanaman budidaya sangat tidak diharapkan, karena dapat menghambat pertumbuhan dan menurunkan produksi tanaman. Hal ini terjadi karena antara tanaman budidaya dan gulma bersaing dalam mendapatkan unsur- unsur hara dari tanah, air tanah, ruang untuk tumbuh dan ca- haya matahari. Bahkan jenis-jenis gulma tertentu mengeluarkan suatu zat yang menghambat pertumbuhan tanaman (alelopa- ti). Masalah gulma sendiri timbul karena adanya kesalahan manusia dalam mengolah lingkungannya, seperti perubahan ekosistem pertanian dalam mengadakan pembajakan, pencangkulan, pemupukan, pengairan, dan penggunaan bahan-bahan kimia, yang secara tidak langsung maupun langsung memacu pertumbuhan gulma (Tjitrosoedirdjo, Utomo, dan Wiroatmodjo, 1984). Sifat-sifat umum yang dimiliki gulma adalah kemampuan menyesuaikan diri yang kuat, serta daya persaingannya yang tinggi. Sifat-sifat yang lain yang biasanya dimiliki oleh gulma adalah potensi penyebaran yang besar, membentuk banyak biji, dan mempunyai sifat istirahat (dormansi) yang lama (Tjitrosoedirdjo et al, 1984)...
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Judul: Dinamika Populasi Gulma Pada Tanaman Padi Gogo dan Kacang Panjang di Kebun Percobaan Biotrop
Abstrak: Gulma merupakan salah satu faktor penghambat di dalam menurunkan hasil tanaman budidaya akibat daya kompetisinya yang kuat dalam hal pengambilan unsur hara, air, udara dan ruang. Menurut Sastroutomo (1983) Gulma dapat mempengaruhi aktivitas manusia dalam bercocok tanam dan pada daerah- daerah yang bukan pertanian lainnya dalam pelbagai cara antara lain: a. Gulma dapat menjadi parasit pada tanaman pangan. b. Gulma dapat meracuni. c. Gulma tidak dapat dimakan, miskin akan kandungan vitamin atau dapat mencemari produksi peternakan. d. Sifat-sifat fisik dan morfologis gulma yang menjadi masalah. e. Investasi gulma yang cukup luas dapat menyebabkan kerusakan pada mesin-mesin pertanian pada saat pemanenan. f. Gulma dapat merupakan tuan rumah dari hama dan penyakit yang dapat mempengaruhi tanaman pangan.
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Judul: Thermal Characteristics and Dynamics of Tropical Cyclone over Western North Pacific Ocean: A Case Study of Typhoon Songda (Chedeng) 2011
Abstrak: The frequent occasion of Tropical Cyclone (TC) over Western North Pacific (WNP) Ocean lies from 10˚N to 26˚N and 121˚E to 170˚E. Sources of TC development come from warm ocean temperature where latent heat is released during condensation processes and subsequently concentrated in the boundary layer. Relative humidity at 850-700 hPa is responsible to produce the most intense storm. Meanwhile, weak vertical wind shear between 850-200 hPa is one of the dynamical factors that lead to the development of TC. Pressure level of 850-200 hPa is chosen to minimize the thermodynamic effect in the lower troposphere. Typhoon Songda (Chedeng in the Philippines) or TSC lasted from May 18th to 30th, 2011 and strengthened into powerful Super Typhoon stage between May 24th and 27th. Long curving track and the exhibition of all sequences of TC life cycle, TSC is then considered as an ideal case of TC. The objective of the study with case of TSC is to investigate the role of thermal characteristics and dynamics on TC intensity. The research is carried out by using Advanced Research of Weather Research and Forecasting model (WRF ARW model) version 3.3. Two domains are employed in the model. The first domain situate from 02˚N to 40˚N and 118˚E to 149˚E and cover spatial resolution () of 33.1 km. The second domain situate from 09˚N to 27˚N and 119˚E to 132˚E with of 11 km. Timestep of the model () is 120 seconds. The model is supported by the following physical parameterization, i.e., Yonsei University Scheme (YSU) in the boundary layer, Kain-Fritsch scheme (KF) in the cumulus, and WRF Single-Moment 3-class scheme in the microphysics. Initial meteorological condition prior to the formation of the cyclone is generated using WRF ARW standard-release model. Sensitivity of the model output is obtained from a selected single-parameter change scenarios, namely, 10 % to 20 % decrease and increase of wind shear initial data at 850-200 hPa, and by 10 % to 20 % decrease of relative humidity initial data at 850-700 hPa. The result showed that the negative correlations between wind shear and intensity are found in wind shear scenarios. Wind shears of 10 ms-1 which lead to strengthening of the wind intensity in the early period of Typhoon development are found in wind shear scenarios. The effect of wind shear changes on wind intensity is statistically significant in the 20 % wind shear scenarios. During mature stage, weak wind intensity occurred when wind shear increase as given in the WRF standard-release and the 20 % decreasing scenario. Different situation is found in the 20 % increasing scenario where wind shear tend to weak and lead to strong wind intensity at this stage. Meanwhile, the reduction of moisture supply at 850-700 hPa resulting from 20 % decreasing relative humidity play a major role in the weakening of wind intensity and reduces mechanical energy of the cycle process as much as 300 J kg-1.
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