Karakteristik Tanah-tanah dari Bahan Induk Abu Volkan Muda di Jawa Barat dan Jawa Tengah

Abstract

Abstrak: Tanah-tanah yang terbentuk dari abu volkan muda umumnya mempunyai sifat-sifat unik dan berpotensi tinggi untuk pertanian. Tujuan penelitian adalah untuk menentukan perbedaan sifat-sifat fisik-kimia dan komposisi mineral tanah-tanah yang berasal dari bahan induk abu volkan muda di Jawa Barat dan Jawa Tengah. Lima profil tanah abu volkan muda berasal dari lereng utara G. Tangkubanperahu (SL-325), lereng timur G. Ceremai (SA-44), lereng barat G. Jembangan (HK-603), dan lereng utara G. Slamet (TG-5 dan YP27) telah dipilih dan dideskripsi sifat-sifat morfologinya di lapangan, dan sebanyak 22 contoh telah dianalisis sifat-sifat fisik-kimia dan komposisi mineral pasirnya. Hasil penelitian menunjukkan bahan induk tanah dari G. Tangkubanperahu dan G. Jembangan bersifat intermedier, yang didominasi oleh plagioklas intermedier, amfibol dan piroksen serta gelas volkan. Bahan induk dari G. Ceremai dan G. Slamet bersifat lebih basis yang dicirikan selain oleh kandungan mineral-mineral tersebut juga terdapat mineral olivin. Cadangan mineral mudah lapuk masih cukup tinggi (41-84%). Tanah dari G. Tangkubanperahu bertekstur lempung berdebu, reaksi tanah masam, dan kejenuhan basa rendah. Tanah dari G. Jembangan bertekstur liat yang menunjukkan tanah lebih berkembang, reaksi tanah masam dan kejenuhan basa rendah. Sedangkan tanah dari G. Ceremai bertekstur lempung berpasir, reaksi tanah netral dan kejenuhan basa sangat tinggi. Tanah dari G. Slamet bertekstur lempung sampai lempung berliat, reaksi tanah agak masam dan kejenuhan basa sangat tinggi. Semua profil memenuhi persyaratan sifat andik [(BD <0,90 g cm-3, retensi P >85%, (Alo+0,5Feo) ekstraksi asam oksalat > 2,0%)], dan karenanya tanah tersebut diklasifikasikan sebagai Andisols pada tingkat Ordo menurut Soil Taxonomy.

Abstract. The soils formed from volcanic ash have unique properties and high potential for agriculture use. The objective of the research was to study the differences between physical-chemical properties and mineral composition of volcanic ash soils in West Java and Central Java. Five volcanic ash soil profiles, from northern slope of G. Tangkubanperahu (SL-325), eastern slope of G. Ceremai (SA-44), western slope of G. Jembangan (HK-603), and northern slope of G. Slamet (TG-5 and YP27), have been selected and described their morphological properties in the field, and as many as 22 soil samples have been analyzed their physical and chemical properties and sand mineral composition. The results showed that the soil parent materials of G. Tangkubanperahu and G. Jembangan were intermediary, dominated by intermediary plagioclase, amphibole, pyroxene, and volcanic glasses. The soil parent materials of G. Ceremai and G. Slamet were more alkaline as characterized by those minerals and olivine content. The content of easily weathered minerals reserves were high (41-84%). The soil properties of G. Tangkubanperahu were silt loam texture, acid soil reaction, and low base saturation. The soil properties of G. Jembangan were clay texture, which showed the more developed soil, acid soil reaction, and low base saturation. Whereas the soil from G. Ceremai has a sandy loam texture, a neutral soil reaction, and a very high base saturation. The soil of G. Slamet is of loamy to clay loamy texture, slightly acid soil reaction, and very high base saturation. All of the soil profiles met the andic properties requirements [(BD <0.90 g cm-3, P retention >85%, and (Alo + 0.5 Feo) oxalic acid extraction >2.0%)], and therefore the soils were classified as Andisols at the Order level according to the Keys to Soil Taxonomy.