Daya Mengembang dan Mengerut Montmorillonit I: Pengaruh Intensitas Curah-Embun terhadap Pengolahan Tanah Vertisol di Kecamatan Tepus dan Playen, Pegunungan Seribu Wonosari - Riset Laboratorium

Abstract

The laboratory study of Montmorillonite clay type on Vertisols from Gunungkidul Regency was accomplished to know the response of some soil characteristics again moisture application by the simulation of rain fall and rain dew. Two naturally peds substances which have high COLE (coefficient of linear extensibility) value (> 0.06) were used with >30 cm diameter, as Ka peds from Karangasem (Tepus district) and as Gd peds from Gading (Playen district) villages. These soil samples were treated by two dosages of aquadest spraying 24 hours a day for 33 days as simulation of rain falls and 12 hours a day for 20 days as simulation of rain dews processes. The soil peds were filtered each 4 days, with size of: < 2 cm, 2 - 4 cm, 4 - 6.4 cm and > 6.4 cm. Results of study: 1. Karangasem soil has clay and organic matter content higher than Gading soil, so Karangasem soil has lower BD value at moist and dry condition than Gading soil.2. Clay, organic matter content and C/N ratio have higher value; it contributes in increasing micro pores and total soil porosity, it provokes the higher soil water holding capacity.  3. The COLE value and clay content of Karangasem soil (on coral materials) have higher than Gading soil (on marl materials), so Karangasem soil has very high shrink and swell capacity which causes the crushing peds more intensive than that on Gading soil. 4. The effect of intermittent rain dew is stronger than continuous rain fall as “crusher agents”, especially for Karangasem soil which has high COLE value; oppositely the continues rain fall crushes effectively for Gading soil with lower COLE value.

ABSTRAK

Kajian laboratorium mineral Monmorillonit dari Vertisol Gunung kidul dilaksanakan agar meminimalkan pengaruh faktor lingkungan. Tujuan penelitian, untuk mengetahui tanggapan sifat Vertisol, terhadap kehadiran lengas. Bongkah Vertisol (utuh ukuran 30 cm) berasal dari dua tempat di Kab. Gunung kidul, yaitu: contoh Ka dari Karang asem (Kec. Tepus) dan contoh Gd dari Gading (Kec. Playen). Kedua bongkah tanah mempunyai sifat kembang kerut kuat, bernilai COLE (koefisien muai panjang) > 0,06. Bongkah Vertisol disemprot aquadest dengan 2 takaran (disemprot 24 jam se- lama 33 hari dan disemprot 12 jam malam hari saja selama 20 hari) untuk menirukan lengas curah hujan awal musim hujan maupun curah embun pada malam hari. Pengayakan dilakukan setiap 4 hari sekali dengan ukuran: < 2 cm, 2-4 cm, 4-6,4 cm dan > 6,4 cm. Hasil penelitian: (1) Tanah Karang Asem mempunyai kadar lempung dan kadar bahan or- ganik lebih tinggi dari tanah Gading, sehingga bernilai BV rendah. (2) Nilai kadar lempung, bahan organik dan nisbah C/N yang tinggi pada tanah Karang asem meningkatkan jumlah pori mikro tanah serta porositas total tanah. (3) Nilai COLE dan kadar lempung bongkah tanah Karang Asem (dari terumbu koral) lebih tinggi dari bongkah tanah Gading (dari napal), sehingga mempunyai daya kembang kerut tinggi yang menyebabkan penghalusan bongkah tanah Karang asem lebih intensif. (4) Curah embun berselang lebih berperan dari pada curah hujan yang berturut-turut terhadap penghalusan bongkah tanah terutama pada tanah Karang Asem, yang mempunyai nilai COLE tinggi.