Judul: Correlation between Redox Potential (Eh) with Fate of Mn and Fe in Paddy Soil and its Relation to Potential of Mn Toxicity in Rice.
Abstrak: Rice plantation using SRI technique gives higher yield production than conventional rice plantation system, but its application does not grow well in Indonesia. In some areas, SRI was reported to have almost similar yield with the conventional. It was particularly occurred in plantation in rainy season with high dosage of organic material. In that field, the plant shows reddish yellow colored leaves. This symptom is regarded as specific indicator of manganese toxicity in rice. Organic material addition in high dosage decreases soil Eh and increases Fe and Mn solubility. However, Fe and Mn solubility does not always correlate with soil Eh and Fe2O3 and MnO2 content in soil. There were some areas which were estimated to have low content of MnO2 but the symptom is still observed. Therefore, the correlation of redox potential with Mn and Fe behavior in paddy soils which are enriched by organic material should be studied in order to determine measuring rod of potential Mn toxicity on rice. Soil samples in this research were taken from Cihideung (Bogor), Bobojong (Cianjur), Margakaya (Karawang), and Kaserangan (Serang). Organic material was added in various comparison into each sample, then the mixtures were flooded for several days. Eh and pH measurements were done during the flooding period. Fe and Mn contents in dry soil were determined with extraction using citric acid 2%, DTPA 0.005M, HCl 0.1N, and DCB. After flooding, Fe and Mn contents in soil were determined with DTPA 0.005M and HCl 0.1N. Fe and Mn contents in soil solution were also determined by AAS. The results showed that the decreasing of Eh was happened faster in soil having high value of pe+pH and low content of Fe2O3. Paddy soil of Cihideung (Bogor) which was added with organic material such as in SRI application has high potent to cause Mn toxicity in rice due to its high content of Mn and low Fe/Mn ratio. Fe and Mn in paddy soil from Margakaya (Karawang) and Kaserangan (Serang) were relatively low, so that those soils do not have potent to cause Mn toxicity on rice plant. Keywords: Mn toxicity, SRI, paddy field
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Judul: Ambang Batas Fe dalam Pupuk Organik yang Berpotensi Menyebabkan Keracunan Fe Pada Tanaman Padi Sawah
Abstrak: Many scientists reported that intensive agricultural using a high rate of in anorganic NPK fertilizer and pesticide, caused declining in soil productivity, soil degradation, and increased environmental pollution. Organic content of these soils are mostly very low, while it is widely know that organic matter is very important to keep physical, chemical, and biological properties of soil as well as soil productivity. However, the quality and quantity of organic matter to be used are important factor determining the impact on the soil. In Ministry of Agriculture Decree (Permentan) No. 28, 2009, a maximum limit of total iron content in organic fertilizer is 8.000 mg kg-1 while most of the current organic fertilizers available in the market exceed this limit. The objectives of the study were to know the quality of organic fertilizer currently available in the market in Java Island and to determine the threshold level of iron that potentially cause iron toxicity in rice. The survey was conducted on May to July 2011 in java Island for survey and collecting a number of organic fertilizer currently marketed and the pot experiment was conducted on May to November 2011 in green house. This experiment using a randomized complete block design with two factors; the types of soil (Endoaquert, Tropaquept, and Hapludult) and organic fertilizer enriched with Fe (FeCl3) in various level. Each treatment was replicated three times. Survey results from 60 samples of granule organic fertilizer taken from several areas in Java Island with 11 parameters, there was indicated two samples (3 % from the total samples) that fulfilled several criteria following of Permentan No. 28, 2009 and no sample (0%) that fulfilled several criteria following of Permentan No. 70, 2011. The pot experiment results showed that the threshold of total iron content in granule organic fertilizer potentially cause iron toxicity for Endoaquert, Tropaquept, and Hapludult were 62.900, 37.300, and 61.100 mg kg-1 respectively. The threshold of total iron content in granule organic fertilizer potentially cause iron toxicity in rice of IR 64 variety with dose 1 ton/ha is 59.500 mg kg-1.
Keyword: Iron, threshold, organic fertilizer, iron toxicity, wetland rice

Judul: Closed Knight’s Tour pada Papan Catur Berbentuk Persegi Panjang dengan Ukuran Maksimal 8 × 8
Abstrak: Closed Knight’s Tour merupakan langkah kuda yang mengunjungi setiap kotak pada papan catur tepat satu kali dengan langkah kuda berawal dan berakhir pada kotak yang sama. Graf yang terbentuk dari closed knight’s tour dinotasikan sebagai graf G(m,n), dengan m adalah banyaknya baris dan n adalah banyaknya kolom. Graf tersebut memuat Hamiltonian cycle. Sebuah graf terhubung G adalah graf bipartite jika dan hanya jika graf tersebut tidak memiliki cycle dengan panjang ganjil. Papan catur yang memenuhi syarat cukup untuk memiliki closed knight’s tour adalah papan catur berukuran 5 × 6, 5 × 8, 6 × 6, 6 × 7, 6 × 8, 7 × 8, dan 8 × 8.
Keyword: bipartite, closed knight’s tour, hamiltonian cycle, knight’s tour, teori graf