Judul: Pyrite and weathered jarosite inactivation of  acid sulphate soil by leaching and biofilter use
Abstrak: The experiments were conducted in the Laboratory of Soil Chemistry and Fertility, Faculty of Agriculture, IPB from March to July 2009, and greenhouse of Indonesian Research Institute for Swampland Agriculture (IRISA), Banjarbaru, South Kalimantan, from October until May 2010. The study was aimed to: (1) investigate the effectiveness of leaching water sources for reducing Fe2+, total-Fe, SO4 2-, and Al3+ concentration in leachate and soil at Eh values of -100 to 400 mV, (2) study the effect of leaching water source (fresh water, brackish water, and peat water) on concentrations of Fe2+, total-Fe, and SO4 2- in leached and soil of acid sulphate soil, and (3) study the effect of leaching water source, root volume (biofilter plant area/pot) and kind of biofilter plants on reducing concentration of Fe2+, total-Fe, and SO4 2- in leached and soil. The results showed that brackish water increased concentration of Fe2+, total-Fe, and Al3+ in leachate, while peat water increased concentration of SO4 2- in leachate. The higher concentration of Fe2+ was found at Eh condition of 100 mV in leachate, while the higher concentration of total-Fe, SO4 2-, and Al3+ was found at Eh condition of 400 mV. Chemical analysis of soil after leaching for eight weeks showed that brackish water decreased concentration of Fe2+ and Al 3+ in soil, while peat water decreased concentration of total-Fe and SO4 2- in soil. Eh condition at 200-300 mV reduced lower concentration of Fe2+ in soil, while at 400 mV reduced concentration of total-Fe, SO4 2-, and Al3+ in soil. During the leaching process, the concentration of Fe2+, total-Fe, and SO4 2- in leachate were decreased. The decrease of that concentrations in the first period was greater than that in the second period. Leaching by brackish water was more effective than by fresh water or peat water in lowering the concentration of Fe2+ and total-Fe in leached. Whereas, leaching by using peat water was more effective to decrease the concentration of SO4 2- compared other treatments. Leaching water sources had no significant effect in improving growth and yield components of Margasari rice variety, but significantly increased dry weight and yield of rice. Dry weight and yield of rice were higher on soil leached by peat water and fresh water than those on soil leached by brackish water. Eliocharis dulcis showed greater ability than Eleocharis retroflaxa to decrease the concentration Fe2+, total-Fe, dan SO4 2- in leachate. Increasing root volume (biofilter plant area/pot) of biofilter plants increased the plant ability in reducing the concentration of those ions in leachate. The leaching water sources had no consistent effect on the difference of Fe2+, total-Fe, and SO4 2- concentration in leachate.
Keyword: Leaching Process, Pelindian, Biofilter, Air Insitu

Judul: Application of steel slag, dolomite, silica gel, and micro fertilizer in rice plant on peat soil
Abstrak: Steel slag as a by-product formed in the process of steel manufacturing consists of iron-making slag or blast furnace slag (BFS) and steel-making slag or electric furnace slag (EFS) had been used as Si fertilizer and liming materials. Steel slag containing silicate, micro elements, and bases can be used to improve chemical properties of peat soil that are poor in nutrients. Steel slag contains a lot of silicate needed by especially Si accumulator plants such as paddy rice plant. This research aimed to compare paddy rice plant’s response of IR64 and Air Tenggulang to EF slag, BF slag, dolomite, silica gel and micro fertilizer application for improving chemical properties of peat soil, to know the reason of paddy rice plant’s response on peat soil to steel slag application and to evaluate steel slag effect in content of hazardous heavy metal in brown rice. This research consisted of an incubation and a greenhouse experiments. Both of them were single factor experiment arranged in a completely randomized design. The treatments were both EFS and BFS (0%, 2%, 4%, 6%, 8% w/w of the soil), both dolomite and silica gel equivalent EFS dosage and also micro nutrients with three replications. The results showed that application of EFS on peat soil significantly improved the availability of Fe and Mn, BFS on peat soil significantly improved the availability of Si and Mg and dolomite on peat soil significantly improved soil pH and availability of Ca. Paddy rice grown on peat soil highly responded to steel slag application. Plant height, number of tillers, weight of spikilets, SiO2 of straw were significantly raised with EFS application and content of hazardous heavy metal in brown rice still within limit of food maximum pollution, but Pb and Hg were not detected. In general, the highest rice yield was achieved at dosage of EFS 8%. In conclusion, paddy rice grown responded to steel slag application was associated in increasing soil pH, the availability of Ca, Mg, Fe, Mn and Si on peat soil. Generally, Paddy rice grown on peat soil highly responded to EFS application better than the others. It meaned that not only silicate as the main factor in improving peat soil chemistry and rice yield, but also increasing soil pH, availability of Ca, Mg and micro nutrients.
Keyword: 

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