Hikmatullah, Kusumo Nugroho and Muhrizal Sarwani
The large lowland peat soils of Indonesia are distributed in various physiographic positions in Sumatra, Kalimantan and Papua islands and have important role in contributing carbon emission. The objective of this study was to characterize the physical and chemical properties of cultivated lowland peat soils in two experimental sites in Kalimantan. Site-1 (5.01 ha) was in Central Kalimantan at the margin of peat dome cultivated with rubber plantation, whereas site-2 (6.72 ha) was in South Kalimantan at the alluvial depression cultivated with paddy rice and maize. Eight representative peat soil profiles from the detailed soil mapping of both sites were selected and 43 soil samples were analyzed for physical and chemical properties. The results indicated that the peat soils of both sites showed different properties in term of degree of decomposition, thickness, ash content, soil acidity, and depth of water table. In site-1, the peat decomposition varied from hemic to sapric with thickness of 5.2-7.0 m and deep water table, while in site-2 the peat decomposition was mostly fibric with thickness of 0.6-2.3 m and shallow water table. The soil bulk density of site-1 was higher than those of site-2 and correlated to fiber content (R2=0.45). The ash contents of sites-1 were lower than those of site-2 and correlated to organic C content (R2=0.68 and 0.89). The soil pH of both sites was very strongly acid, however, in site-1 it was more acid (pH 3.4-3.7) than of site-2 (pH 3.9-4.7) indicating these soils were low content of exchangeable bases. These soils of both sites were grouped as ombrogenous peat, since they showed low ash content, low nutrient content and very acid reaction. This study also showed that physiographic position influences the properties of peat soils, and consequently it would influence the magnitude of carbon stocks and carbon emission.
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