KAJIAN SIFAT FISIKA TANAH PADA BEBERAPA PENGGUNAAN LAHAN DI KENAGARIAN SITANANG, KECAMATAN AMPEK NAGARI, KABUPATEN AGAM

KAJIAN SIFAT FISIKA TANAH PADA BEBERAPA PENGGUNAAN LAHAN DI KENAGARIAN SITANANG, KECAMATAN AMPEK NAGARI, KABUPATEN AGAM ABSTRAK Penelitian mengenai kajian sifat fisika tanah pada beberapa penggunaan lahan dengan kelerengan 8-15% telah dilaksanakan pada ordo Ultisol di Kenagarian Sitanang, Kecamatan Ampek Nagari, Kabupaten Agam dari bulan Juni hingga Agustus 2016. Pengambilan sampel berdasarkan metode survei secara purposive random sampling untuk lima penggunaan lahan (hutan sekunder, kebun campuran, semak belukar, kebun karet, dan kebun sawit). Tujuannya adalah untuk mengkaji beberapa sifat fisika tanah meliputi tekstur tanah, berat volume (BV), total ruang pori (TRP), kadar air tanah (KA), permeabilitas tanah, indeks stabilitas agregat tanah serta bahan organik tanah (BOT) pada kedalaman 0-20 cm dan 20-40 cm. Konversi lahan hutan menjadi lahan pertanian tersebut telah berdampak terhadap perubahan BOT yang mempengaruhi sifat fisika tanah, seperti BV, TRP, KA tanah, permeabilitas tanah, dan indeks stabilitas agregat tanah. Data penelitian menunjukkan perubahan penggunaan lahan dari hutan sekunder menjadi kebun campuran, semak belukar, kebun karet dan kebun sawit menyebabkan penurunan kandungan bahan organik pada kedalaman 0-20 cm berturut-turut sebesar 18%, 27%, 55%, dan 61% dan pada kedalaman 20-40 cm adalah 27%, 27%, 48%, dan 72%. Dari hasil penelitian diperoleh data bahwa nilai BV pada lahan tersebut adalah 0.72 g cm-3, 0.79 g cm-3, 0.80 g cm-3, 0.92 g cm-3, and 1.04 g cm-3 pada kedalaman 0-20 cm dan 0.83 g cm-3, 0.82 g cm-3, 0.96 g cm-3, 1.01 g cm-3, dan 1.24 g cm-3 pada kedalaman 20-40 cm. Nilai tertinggi dari TRP (73.18%), permeabilitas (9.32 cm jam-1), dan indeks stabilitas agregat (78.80) didapatkan pada penggunaan lahan hutan sekunder kedalaman 0-20 cm. Disimpulkan dari hasil penelitian bahwa sifat fisika hutan sekunder > kebun campuran> dan indeks stabilitas agregat semak belukar > kebun karet > kebun sawit. Sifat fisika tanah yang kurang baik didapatlan pada kebun sawit (BV, TRP, permeabilitas, dan indeks stabilitas agregat). Kata kunci : bahan organik, konversi lahan, penggunaan lahan, sifat fisika tanah STUDY OF PHYSICAL PROPERTIES ON SEVERAL TYPES OF LAND USE IN KENAGARIAN SITANANG, KECAMATAN AMPEK NAGARI, AGAM REGENCY ABSTRACT A research on physical properties of Ultisols having 8% to 15% slope under several types of land use was conducted in Kenagarian Sitanang, Kecamatan Ampek Nagari, Agam Regency from June to August 2016. This research used survey method, samples were randomly taken (purposive random sampling) for each land use, they are secondary forest, mix garden, shrub, rubber plantation, and oil palm plantation. This study was aimed to determine physical properties of soil under different land use after being converted from forest. Parameters analyzed were soil texture, soil organic matter (SOM), bulk density (BD), total porosity (TP), soil moisture content, soil permeability, and index of soil aggregate stability at 0-20 cm and 20-40 cm soil depth. Results showed that SOM decreased as secondary forest was converted into mix garden, shrubs, rubber plantation, and oil palm plantation by 18%, 27%, 55%, and 61% at 0-20 cm soil depth and by 27%, 27%, 48% and 72% at 20-40 cm soil depth, respectively. This research indicated that BD by 0.72 g cm-3, 0.79 g cm-3, 0.80 g cm-3, 0.92 g cm-3, and 1.04 g cm-3 at 0-20 cm soil depth and by 0.83 g cm-3, 0.82 g cm-3, 0.96 g cm-3, 1.01 g cm-3, and 1.24 g cm-3 at 20-40 cm soil depth. However, the highest of total porosity (73.18%), soil permeability (9.32 cm h-1) and index of soil agregate stability (78.80) were found under secondary forest on depth 0-20 cm. It can be concluded that the physical properties of the secondary forest > mix garden > shrubs > rubber plantation > oil palm plantation. Soil physical properties under oil palm land use was the poorest among the land use studied (SOM, BD, TP, soil moisture content, soil permeability, and index of soil aggregate stability). Keywords: land conversion, land use, soil organic matter, soil physical propertie