Keberadaan bahan Amorf dan hubungannya dengan sifat kimia Andisol dari Kecamatan Ponjong unung Kidul Jogjakarta

RATNADI, Faisol, Dr.Ir. Eko Hanudin, MS

2004 | Tesis | S2 Ilmu Tanah

Penelitian ini dilakukan di bukit karst Gadung dengan ketinggian tempat 460 meter di atas permukaan laut (m dpl), bukit karst Gangsir (300 m dpl) dan bukit karst Gatel (450 m dpl) yang terletak di desa Bedoyo Kulon, Kecamatan Ponjong, Kabupaten Gunung kidul, Propinsi Daerah Istimewa Jogjakarta. Tujuan penelitian ini adalah untuk mengetahui keberadaan, jumlah, macam bahan amorf dan hubungannya dengan sifat kimia Andisol. Keberadaan bahan amorf dan hubungannya dengan sifat kimia Andisol dapat diketahui dengan bantuan data-data sifat kimia tanah dan mineralogi lempung yaitu Infra-red dan Differential Thermal Analysis (DTA). Penga mbilan sampel tanah dilakukan pada setiap lapisan profil tanah dan diamati morfologi tanahnya. Analisis sifat kimia tanah dilakukan di laboratorium Ilmu Tanah, sedangkan sifat mineralogi lempung dianalisis di laboratorium Tanah Institut Pertanian Bogor. Dengan teknik pelarutan selektif dan dibantu dengan analisis infra-red spektral serta karateristik termalnya dapat diketahui keberadaan bahan amorf baik berupa allofan, imogolit, ferrihidrit maupun sesquioksida lainnya. Kandungan allofan dan imogolit cukup bervariasi, yang tertinggi ditemui di bukit Gadung muka Timur dan terendah dijumpai di bukit Gangsir muka Barat. Hasil analisis sifat kimianya menunjukkan adanya sifat Andisol, yaitu retensi fosfat ³ 85 %, pH (NaF) ³ 10, kapasitas pertukaran kation ³ 24 me %, C-organik > 6 %, dan nilai (Al-o + 1/2Fe-o) berkisar 1,3 – 2,62. Spektra infra-rednya memiliki empat daerah utama yaitu sekitar 3445, 1654, 910 – 1029, 430-543 cm-1, masing-masing berasal dari vibrasi OH, deformasi HOH, ikatan Si-O-Al dan Si-O terkondensasi. Sifat termalnya memiliki puncak endotermik sekitar 50 ºC – 150 ºC dan eksotermik 800 ºC – 950 ºC.

This study was conducted at three locations, namely: Gadung, Gangsir and Gatel with elevation of 460, 300 and 450 m sea level above, respectively. The locations were situated at karts formation, where included of Ponjong subdistrict, Gunung Kidul, Province of Jogjakarta. The objectives of this research are to find out the existence, quantity, type of amorph materials in andisols and its correlation to the chemical properties. Identification of amorph materials were supported by data of soil chemical properties, differential thermal analysis (DTA) and Infra-red spectral. Soil samples were taken from each layer of soil profiles, as a representative of surface and subsurface soil, respectively. The soil chemical analysis was conducted at soil science laboratory of Gadjah Mada University, and clay mineralogy analysis was done at soil science laboratory of Bogor Agriculture University. Application of selective dissolution technique and supported by infra-red spectral and differential thermal analysis could be identified the existence of the amorph materials in the soil, such as: allophane, imogolit, ferrihydrit, and sesquioxide. The content of allophane- imogolite is so various; the highest one was founded at East Side of Gadung, while the lowest one was founded at western side of Gangsir. The results of soil chemical analysis indicated the andic properties, such as: phosphate retention ³ 85 %, pH (NaF) ³ 10, CEC ³ 24 me %, C-organic ³ 6 %, and (Al-o + ½ Fe-o) of 1.3 – 2.62. Infrared spectral showed four major regions, namely: 3445, 165, 910-1029, and 430-543 cm-1. The maximum band absorption were derived to OH vibration, HOH deformation, Si-O-Al bond, condensed Si-O, respectively. Thermal characteristic showed endothermic peak at 50-150 ºC and exotermic peak at 800 – 950 ºC.

Kata Kunci : Tanah Andisol,Bahan Amorf,Sifat Kimia, Amorph material, Soil chemical properties, Andic properties, Infra-red spectral and Defferential Thermal Analysis (DTA)