The conversion of peat soils to agricultural uses has been thought to increase CO2 emission due to several factors, including fertilization. However, evidence on the effect of fertilization on CO2emissionsfrompeat soils is rareand often inconsistence. We measured the effects of different types of fertilizer, including N, P and K sources, and clay as an ameliorant on CO2 emission from a bare peat soil in Lubuk Ogong, Riau Province. Nutrients were added in the following combinations: 0 (unfertilized plot), N source (urea), slow-release N (slow release urea), N and Psource (Urea+SP-36), N, P and K sources (urea+SP-36+KCl) and combined NPK-Clay. Fertilization resulted in a decreasein CO2 emissions compared to that prior to fertilization except when slow-release urea was applied. Decreasing of CO2 emissions was probably due to pH-related effects because the pH in the N treatment was lower than in both the control and the unfertilized plot. A decreasein the level of CO2 emissions among the treatments followed the order NPK-Clay>NP>NPK>urea>slow-release urea. Covariance analyses showed that the difference in CO2 emissions prior to treatment was not significant. The application of individual and combined treatments of N, P, K and NPK mixed with 5 Mg ha-1 clay led to significantly reduced CO2 emissions from bare peat soil in Lubuk Ogong, Riau Province. In addition to fertilization, the water table depth was the only parameter that significantly affected the CO2 emissions (P<0.05). We conclude that the application of nutrient combinations, including N, P, K and clay, could reduce CO2 emissions because these treatments maintain a balanced nutritional condition in the soil with respect to the microbial activity.Keywords: Amelioration, CO2 emission, fertilization, tropical peat soils

Masalah utama yang dihadapi dalam pengembangan perkebunan kelapa sawit rakyat antara lain adalah rendahnya produktivitas karena kelapa sawit sebagian besar dibudidayakan di lahan gambut yang rendah kesuburan tanahnya serta relatif rendahnya input hara. Peningkatan produktivitas kelapa sawit di lahan gambut dapat dilakukan melalui penggunaan amelioran dari tandan buah kosong yang dibuat menggunakan dekomposer. Penelitian dilaksanakan pada Januari-Desember 2016 di lahan kebun kelapa sawit milik petani yang berumur sekitar lima tahun di Kabupaten Pelalawan, Provinsi Riau, Indonesia. Penelitian bertujuan untuk menentukan jenis dekomposer yang terbaik untuk pembuatan kompos tandan buah kosong sehingga dapat meningkatkan produktivitas kelapa sawit yang dibudidayakan di lahan gambut. Penelitian menguji berbagai dekomposer yang digunakan dalam pembuatan kompos tandan buah kosong (Ktd) tanpa dekomposer, Dekomposer sd (K-sd), Dekomposer bm (K-bm), Dekomposer ol (K-ol), Kompos tp (K-tp), dan dekomposer em (K-em). Perlakuan ditata dalam rancangan acak kelompok (RAK) dengan tiga ulangan. Pengamatan dilakukan terhadap sifat kimia tanah sebelum aplikasi pemupukan pertama dan setelah 6 bulan kemudian, kualitas kompos, dan respon tanaman kelapa sawit. Hasil penelitian menunjukkan bahwa pertambahan pelepah daun tidak dipengaruhi oleh perlakuan, tetapi pertambahan berat pelepah, dan produktivitas sangat dipengaruhi oleh perlakuan. Produktivitas tertinggi (1,87 ton ha-1 bulan-1) dihasilkan dari penggunaan amelioran Ksd, yaitu kompos tandan buah kosong mengandung mikroba aerob perombak lignin, selulosa, protein, lipid, asam amino, dan mengandung tricoderma.

The coconut rhinoceros beetle (Oryctes rhinoceros L.) and brown rhinoceros beetle (Xylotrupes gideon L.) (Coleoptera: Scarabaeidae) are insect pests commonly found in oil palm plantations. Availability of breeding sites is one of factors that can increase the beetle population. Therefore, this study aimed to determine the abundance and age structure of the coconut rhinoceros beetles and brown rhinoceros beetles in the breeding sites located in a plantation with immature and mature stage of oil palms. The results of this study indicated that the abundance of coconut rhinoceros beetle was found to be lower than brown rhinoceros beetle (4.47±13.56 compared to 25.23±16.48 individuals/plot) in the oil palm plantations in PTPN VIII Parakan Salak, Sukabumi Regency. The population of coconut rhinoceros beetle was found in the breeding site located in the plantation with mature oil palms, but not found in the location with immature plants. The age structure of coconut rhinoceros beetle was dominated by the 1st and 2nd instar larvae. The age structures of brown rhinoceros beetles in the breeding sites located in the immature and mature oil palm were similar, and they were dominated by the 1st, 2nd, and 3rd instar larvae. Results of correlation analysis show that there is no correlation between soil chemical characteristics of the breeding site and the beetle population. Soil chemical characteristics at the breeding sites in both locations were relatively similar, and consequently, the abundance and age structure of coconut rhinoceros beetle and brown rhinoceros beetle not significantly different between both locations.