Judul: The characteristics of paddy soils at the toposequence with volcanic parent material in Bogor – Jakarta area
Abstrak: The aims of the research were: (1) to study the characteristics and genesis of paddy soils at the toposequence with volcanic parent materials in Bogor . Jakarta area, (2) to study the influence of paddy cultivation intensity on the formation of surface gley, plow pan, Fe and Mn layer, (3) to study the movement of Fe and Mn soil, and (4) to study the mineralogy and classification of the soils. Twelve pedons, selected based on: (1) soils subgroup, and (2) cultivation intensity were investigated. Soil sample were collected from each horizon of the pedons for laboratory analysis. The result of the research shows that the morphology, the non-paddy soils consists only of tillage layer and the original soil layer. The once paddy a year soils, besides the tillage layer, show further horizonisation, including less visible plow pan layer (bulk density slightly higher than the tillage layer), Fe accumulation and Mn accumulation layer, and the original soil layer; meanwhile, the horizon of the twice a year paddy soils are as follows: more visible reduced tillage layer (chroma three month after harvesting . 2), more visible plow pan layer (bulk density clearly higher than the tillage layer above it and the layer below it, and permeability and porosity lower), Fe and/or Mn accumulation layer, and the original soil layer. At higher elevation (Yellowish Brown and Brown Latosols), both the once a year and twice a year of paddy soils, the plow pan layer was found at a shallower depth (10 . 12 cm), while at the lower elevation (Reddish Brown and Red Latosols) it was found deeper (15 . 16 cm), with similar thickness (12 . 19 cm). At higher elevation (Yellowish Brown Latosols), Mn accumulation layer were thicker (72 - 86 cm) than at lower elevation, and in Reddish Brown Latosols (42 - 46 cm). The color of tillage layer of paddy soils is lighter than the lower layer. At harvesting time the chroma 0, three month after harvesting chroma 2, but one year after harvesting if not rice cultivated the colors approach to the original soils colors. The consistence of the tillage layer after harvesting (wet) were very sticky and very plastic, at one to three month no rice cultivation still slightly sticky, but after six to nine month becoming friable to very friable. The pedogenesis processes of paddy soils were Fe/Mn elluviation of tillage layer Fe/Mn illuviation in the lower depth. This indicated by Fed, Feo, and Fep, or Mnd, Mno, and Mnp, and the quantity of Fe or Mn mottles. The tillage layer of paddy soils contain higher weatherable minerals than non-paddy soils, due to mineral materials containing in the irrigation water or mineral material erupted from surrounding volcanoes. In the tillage layer of non-paddy soils, there were processes enrichment, decomposition, lessivage, and leusinization. But of in the paddy soils there were also elluviation and gleyzation. The soil that are regularly cultivated with paddy, there are changes in soil classification, e.i. Typic subgroup of the non paddy soils changes into Aquic subgroup in the once/year paddy soils, and Aquic suborder
Keyword: tillage layer, plow pan layer, manganese layer, iron layer, West Java