Karakteristik kimiawi komponen mineral amorf pada andisol yang berkembang dari tuff volkan gunung api di Jawa Tengah

RATMINI, Niluh Putu Sri, Dr. Ir. Eko Hanudin, MS

2008 | Tesis | S2 Ilmu Tanah

Andisol merupakan tanah yang banyak mengandung mineral amorf, namun penelitian tentang hal tersebut sampai saat ini belum banyak dilakukan di Indonesia. Penelitian ini bertujuan untuk mengetahui karakteristik kimiawi mineral amorf pada andisol yang berkembang dari tuff volkan gunungapi di Jawa Tengah. Sampel tanah diambil dari horison B/C dari Andisol yang terletak di Gunung Slamet, Dieng, Merbabu dan Lawu. Pengambilan sampel mempertimbangkan faktor umur bahan induk (tua dan muda) dan posisi lereng (atas, tengah dan bawah). Karakterisasi mineral amorf dilakukan terhadap fraksi lempung yang diperoleh dengan metode pemipetan (Hukum Stok). Hasil penelitian menunjukkan bahwa pH-H2O memiliki harkat masam sampai agak masam, pH NaF > 11, bahan organik sangat tinggi (20,66%) dengan KPK 40,9 (cmol(+).kg-1). Komponen mineral amorf yang diperoleh tersusun atas alofan/imogolit dan ferrihidrit yang masing-masing berkisar 4,3 – 19,59% dan 1,07 – 5,02% Rata-rata kemampuan dari mineral amorf ini dalam menjerap P > 98%. Identifikasi dengan difraksi sinar-x menunjukkan komponen mineral amorf dari G. Slamet didominasi oleh alofan dan imogolit. Komponen mineral pada sampel dari Dieng tersusun atas Alofan/imogolit, Feldfar, Kaolinit, Metahalloisit, Zeolit dan Kuarsa. Di G. Merbabu muda didominasi mineral alofan dan imogolit, sedangkan di Merbabu Tua merata antara mineral alofan dan imogolit, Kaolinit dan K-Felsfar. Sampel dari G. Lawu menunjukkan bahwa difraktogram sinar-X dari mineral amorf tidak tampak kemungkinan tertutupi oleh difraksi dari Feldsfar. Karakteristik inframerah spektral menunjukkan bahwa pita serapan pertama muncul pada kisaran bilangan gelombang 3449 – 3510 cm-1, merupakan getar regang dari gugus OH dari grup silanol dan aluminol. Pita serapan gugus OH dari air yang terjerap muncul pada kisaran bilangan gelombang 1639 – 1655 cm-1. Pita serapan muncul pada kisaran bilangan gelombang 559 – 567 cm-1 dan 910-972 cm-1, yang merupakan getar regang dari gugus Si-O-Al. Pita serapan gugus Si-O muncul pada kisaran bilangan gelombang 471 –570 cm-1 dan 1033 - 1030 cm-1.

It is known well that Andisol is a soil with high content in amorphous minerals. However, information on chemical characteristic of amorphous minerals still scarce, a particularly in Indonesia. The main objective of the research was to find out the chemical characteristics of the amorphous minerals of Andisol collected from 4 mountaints located in Cenral Java. Soil samples was taken out from B/C Horizon from Mt.Slamet, Dieng, Merbabu and Lawu. Soil sampling consider a representative of the age of the parent materials (old and young formation) and position in the slope (upper, midel and lower). Characterization of the amorphous minerals was conducted for clay fraktion by applying the pipet method (Stok’s Principle). The results indicated that pH-H2O was categorized as acid to moderate, pH NaF > 11, a high content in organic material (20.66%) and CEC 40,9 cmol(+).kg-1. The amorphous minerals were composed of allophane/imogolite and ferryhidrate with a range content of 4,3 – 19,59% and 1,07 – 5,02% respectively. The P absorption capacity in average was higher than 98%. The Xray diffraction indicated that the amorphous minerals from Mt. Slamet were dominated by allophane and imogolite. The minerals components from Mt. Dieng were composed of allophane and imogolite, feldsfar, kaolinite, metahalloisite, zeolite and quartz. For the Young Formation Merbabu was dominated by allophane and imogolite, whereas for the Old Formation Merbabu was composed of allophane, imogolite, kaolinite and K-feldsfar. Sample from Mt. Lawu indicated that the X-ray diffractogram was not identified, this was likely due to the peak was covered by the higher peak from feldsfar. Infrared spectral characteristics of the amorphous material indicated that the absorption bands of the first region appeared at a range of 3440-3510 cm-1, the band due to streching vibration of hydroxyl (OH) groups either as structural OH or as adsorbed water. The absorption bands of HOH from adsorbed water appeared ranging from 1639- 1655 cm-1. The maximum adsoprtion bands were observed appeared ranging from 559 – 567 cm-1 and 910-972 cm-1, the bands are due stretching vibration of Si-O-Al. The absorption bands of Si-O or Al-O appeared ranging from 471 –570 cm-1 and 1033 - 1030 cm-1.

Kata Kunci : Andisol,Alofan,Imogolit,X,RD,Infrared Spektra, Andisol, allophane, imogolite, X-RD, and Infrared Spektra