A detailed spatial inventory of the extent and depth distribution for tropical peatlands is not currently available; however, there is a critical need for new detailed peatland information at national, regional and global scales. Hence, the objective of this study was to provide a rigorous assessment of the extent and depth distribution of tropical peatlands in Indonesia. Data were acquired using a standard method protocol of semi-detailed peatland mapping programs (1:50 000 scale) from 2013 to 2019 for all Indonesian peatlands. Arc-GIS and multi-source satellite images (Landsat ETM-7, Landsat 8 OLI, ALOS, SPOT-5 and SPOT-6/7, and DEM/SRTM) were used to delineate soil-mapping units (polygons) which were supported by depth observation points derived from databases of soil maps 1:50 000 and peatland maps 1:250 000, and then subsequently verified with rigorous groundtruthing. Field transects were made between rivers using systematic distances to observe peat morphological features and thickness resulting in a total of 18,232 data points that included 14,185 new observations and 4,047 legacy points. Our results provide the first systematic census for all Indonesian peatlands and showed that peatlands occupied 13.43 million ha distributed on four islands (million ha): Sumatera (5.85) > Kalimantan (4.54) > Papua (3.01) > Sulawesi (0.024). Peat depth was classified into six categories: D1(50-<100 cm), D2 (100-<200 cm), D3 (200-<300 cm), D4 (300-<500 cm), D5 (500-<700 cm) and D6 (=700 cm), which represented (million ha/peatlands%) 3.17 (24%), 3.44 (26%), 2.61 (19%), 2.32 (17%), 1.29 (10%) and 0.59 (4%), respectively. Exceptionally deep (=700 cm) peatlands occurred on Kalimantan and Sumatera Islands, but were not found on Papua and Sulawesi Islands. The present peatland extent (13.43 million ha) was smaller than previous estimates (pre-2012) that varied from 14.9 to 27.0 million ha. The smaller peatland extent in the present semi-detailed mapping inventory (1:50 000) than previous estimates (pre-2012) may result primarily from (i) segregation of mineral soil inclusions previously considered as peatland, (ii) improved remote sensing and GIS tools (e.g., DEM/SRTM) that prevented misclassification of peatland areas, and (iii) extensive field observation for verification of peatland boundaries and thickness requirements (>50 cm) that eliminated peatlands lost to enhanced decomposition from agricultural management and drainage practices. Our study on peatland extent and thickness provides new detailed information of tropical peatlands in Indonesia (a major region of tropical peatlands) to serve as a baseline for future inventories. The information provided by this study updates peat information for Indonesia (extent and depth), fills a critical knowledge gap for accurately determining regional/global organic C stocks, and informs future directions for the sustainable use and management of tropical peatlands.

Laju pertumbuhan penduduk tidak seimbang dengan laju pertambahan lahan pertanian. Akibatnya, jumlah petani gurem dengan kepemilikan lahan kurang dari 0,50 ha bertambah dari 10,80 juta rumah tangga petani (RTP) pada tahun 1993 menjadi lebih dari 15 juta RTP pada 2010. Selain itu, konversi lahan, degradasi lahan dan air, perubahan iklim, dan kerusakan lingkungan menjadi kendala utama dalam pembangunan pertanian di masa yang akan datang. Apabila konversi lahan dapat ditekan 60.000 ha/tahun dan sawah baru bertambah 67.700 ha/tahun maka luas lahan yang dibutuhkan untuk mempertahankan swasembada beras dan pangan lainnya sampai tahun 2020 secara kumulatif mencapai 1,61 juta ha atau 6,08 juta ha hingga tahun 2050. Untuk lahan kering diperlukan perluasan sekitar 11,75 juta ha menjelang tahun 2050. Apabila kebutuhan energi juga akan dipasok dari bahan baku pangan (jagung, kedelai, ubi kayu, tebu, kelapa, kelapa sawit) maka lahan yang dibutuhkan makin luas. Berdasarkan sifat biofisik, lahan yang sesuai untuk pertanian dan saat ini belum dimanfaatkan mencapai 30,67 juta ha dan 8,28 juta ha di antaranya sesuai untuk sawah. Lahan tersebut belum diketahui status kepemilikannya, tetapi sebagian besar (20,40 juta ha) berada di kawasan hutan (hutan produksi, hutan konversi, HPH) dan 10,30 juta ha berada di kawasan budi daya pertanian. Selain dengan perluasan, pemanfaatan lahan perlu dioptimalkan melalui intensifikasi, peningkatan intensitas tanam (IP200, IP300, IP400), pengembangan inovasi teknologi, perbaikan pengelolaan DAS, konservasi tanah dan air, serta perlindungan lahan terhadap konversi, penelantaran, dan degradasi.

Development of newly opened wetland rice fields both from dry land and wetland in Indonesia are important to meet rice growing demand, increase soil productivity, keep rural food security and provide jobs as well as generate income. Most soils of newly opened rice fields are low in P and K contents, but the farmers do not apply P and K recommended fertilisers. The study was conducted on newly opened wetland rice farming in Panca Agung village, Bulungan District, East Kalimantan Province, Indonesia in 2009. The aims were to evaluate phosphorous and potassium input – out of newly opened wetland rice and to validate the P and K recommendation. Six treatments were tested including farmers practices (as control), farmer practices + straw compost + dolomite, NPK with recommendation rate in which N and K was split in two applications, NPK with recommendation rate in which N and K was split three applications, NPK with recommendation rate + straw compost + Dolomite , in which N and K was split three applications, and NPK with recommendation rate + straw compost + dolomite, in which N and K were split two applications. The N, P and K rates were 250 kg urea, 100 kg SP-36 and 100 kg KCl ha-1 season-1, while the farmer practices 100 kg urea and 100 kg SP-36 ha-1 season-1. Parameters to be measured were concentration P and K in mineral fertilizer, compost, irrigation water and grains as well as straw. The results showed that surplus P ranged from 5.75 to 12.85 kg P ha-1 season-1, meaning that SP-36 application rate was more than enough to replace P removed by harvest product. In contrast, potassium application rate should be increased from 100 to 200 kg KCl ha-1 season-1 to fix K removed by harvest product. However, when the compost will also be increased to 3 Mg ha-1 season-1 K fertilizer can be increased to 150 kg KCl ha-1 season-1 to substitute K taken away by rice harvest product and to keep higher rice grain yield. These P and K recommendation rate imply that total SP-36 and KCl should be available at district level will be about 984.9 Mg SP-36 and 1.477 Mg KCl district -1 season -1, respectively. Keywords: Newly opened wetland rice; nutrient balance; nutrient input; nutrient losses; plot scale wetland [How to Cite: Sukristiyonubowo, K Nugroho and S Ritung. 2012. Plot Scale Phosphorous and Potassium Balances of Newly Opened Wetland Rice Farming Originated from Wetland. J Trop Soils 17 (3): 227-237. doi: 10.5400/jts.2012.17.3.227] [Permalink/DOI: www.dx.doi.org/10.5400/jts.2012.17.3.227 ]

Soils allocated for development of newly opened wetland rice fields in Indonesia can be from dry land or/and wetland to meet rice growing demand. The soils are low in major nutrient contents, but high in Fe concentration. The farmers do not apply N and K fertilisers’ bases on recommendation. The study was conducted on newly opened wetland rice farming originated from wetland in Tanjung Buka SP-2 village, Bulungan District, East Kalimantan Province, Indonesia in 2011. The aims were (1) to evaluate nitrogen and potassium input – out of newly opened wetland rice and (2) to validate the N and K recommendation. The results indicated that surplus N ranged from 39.03 to 71.62 kg N ha-1 season-1 , meaning the amount of urea is more than enough to replace N removed by harvest product. The recommended urea should be reduced to 150 kg urea with added compost of 3 tons ha-1 season-1. If the compost increased to 3 tons ha-1 season-1, K fertilizer can be increased to 150 kg KCl ha-1 season-1 to substitute K taken away by rice harvest product and to keep higher rice grain yield. These N and K recommendation rate imply the total urea and KCl available at district level with about 1,477 tons urea and 1,477 tons KCl district -1 season -1, respectively (150 kg urea x 9,849 ha and 150 kg KCl x 9,849 ha).

Newly opened wetland rice fields require more water because plough pan layer are not developed. Plough pans are established several years and also depending on intensity of planting rice. Plot scale study was conducted at newly opened wetland rice originated from dry land in Panca Agung village, Bulungan District, Indonesia in 2011. Different water pounding depth including 0.5 cm (macak macak) and intermittent (two weeks wetting and a week was drying cycle) were tested. Rice growth, rice grains yield and water productivity was observed. Water productivity was computed according to the ratio between rice grains yield and water input. Water input was predicted according to the difference between incoming water and outgoing water. In this study water balance was not taken into account in calculating the water input. The results indicated that pounding water layer did not significantly improve on plant height, but significantly increased rice tiller number and grains yield. The highest tiller number and grain yield were reached by pounding water depth of 0-3 cm. The higher water productivity of about 0.96 and 0.30 gram liter-1 were recorded by pounding water depth 0.5 cm followed by pounding water layer of 0-3 cm. In a long term perspective, the implementation of this work would certainly contribute to water management and improve rice grains yield of wetland rice in Indonesia as water become scare.