Relationship between landform, lithology and soils in Lower Citarum Watershed, West Java [Indonesia]

anglais. In order to support the semi detail mapping of soils in Lower Citarum watershed, a study on relationships between landform, lithology and soils was carried out. Landform interpretation was done by field observation, air photo interpretation and supported by geological map information. Thirteen soil profiles were made in the field, and seventy soil samples were taken from the profiles for laboratory analyses. The laboratory analyses consist of chemical and mineralogical analyses. Results indicated that from the beach (north) to the hill direction (south) the landform generally can be divided into four groups: marine, fluvio-marine, alluvial and techtonic/structural. In the marine landform, the soil developed from sand, silt and clay marine deposite influenced by relatively permanent flooding (except sandy soils). The soils have no structure development, and their chemical properties influenced by salts, so that the exchangeable cations were dominated by magnesium and natrium, indicating the presence of sulfidic materials, and accumulation of phosphate and potential potassium. To the fluvio-marine direction, the lithology changed. In this landform soil developed from river deposite which was situated above the marine deposite and influenced by fluctuation of ground water. As a result in the fluvio-marine lithologic discontinuity occur, indicate by changing in the exchangeable calcium and magnesium ratio. In the alluvial soil developed under the influence of ground water, but marine sediments did not present anymore, and the lithology was dominated by river sediment. Some soils showed a stratification, acid in the top soil and dominated by exchangeable calcium. The techtonic/structural landform showed a very different condition with the others landform, due to the fact that this landform is resulting from uplifting, folding and foulting processes. The lithology was consolidated like rock, some of them were marine sedimentary rock, and the rest was andesitic volcanic rock. Almost all soils developed under good drainage condition. The flat area of the fluvio-marine and alluvial plain make the soils in this area potentially good for irrigated rice field

indonésien. Untuk menunjang pemetaan tanah semi detail di daerah aliran sungai Citarum Bawah telah dilakukan penelitian mengenai hubungan antara landform, litologi, dan tanah di daerah tersebut. Interpretasi landform dilaksanakan dengan pengamatan di lapangan, interpretasi foto udara, dan ditunjang dengan informasi dari peta geologi. Tujuh puluh contoh tanah dari tiga belas pedon telah dianalisis sifat fisiko-kimia dan komposisi mineralnya di laboratorium. Hasil penelitian menunjukkan bahwa mulai dari arah pantai (utara) ke arah perbukitan (selatan) secara garis besar dapat dibedakan empat grup landform, yaitu grup marin, grup fluvio-marin, grup aluvial, dan grup tektonik/struktural. Pada landform marin, tanah berkembang dari bahan endapan pasir, debu, dan liat dengan pengaruh genangan air yang relatif permanen. Tanah belum mempunyai perkembangan struktur dan sifat kimianya dipengaruhi oleh garam-garam sehingga susunan kation dapat tukarnya didominasi oleh magnesium dan natrium, menunjukkan adanya bahan sulfidik, serta akumulasi fosfat dan kalium potensial. Ke arah landform fluvio-marin terjadi perubahan litologi. Pada landform ini tanah berkembang dari bahan endapan sungai yang terletak di atas bahan endapan marin dan dipengaruhi oleh fluktuasi air tanah. Akibatnya pada landform fluvio-marin terdapat ketidakselarasan bahan induk tanah yang tercermin oleh perubahan nilai bandingan antara kalsium dapat ditukar dengan magnesium dapat ditukar. Pada landform aluvial, pengaruh air tanah masih ada, akan tetapi bahan endapan marin sudah tidak nampak dan bahan dari endapan sungai lebih dominan. Sebagian tanah menunjukkan adanya perlapisan, masam di lapisan atasnya dan kalsium dapat ditukar dominan. Pada landform tektonik/struktural kondisinya jauh berbeda dengan ketiga landform sebelumnya, karena landform ini terbentuk sebagai akibat proses angkatan, lipatan, dan patahan. Litologinya sudah mengalami pemadatan dan berupa batuan, sebagian merupakan batuan marin yang terangkat dan sebagian lagi merupakan bahan volkan andesitik. Hampir semua tanah berkembang dengan kondisi drainase yang baik. Karena posisinya yang datar, menyebabkan tanah-tanah di daerah fluvio-marin dan dataran aluvial umumnya berpotensi baik untuk sawah irigasi