KAJIAN LIMPASAN PERMUKAAN DAN KETERSEDIAAN BAHAN ORGANIK TANAH PADA AGROFORESTRI BERBASIS BAMBU DI KABUPATEN LOMBOK TIMUR

Cecep Handoko, Prof. Dr. Ir. H. M. Sambas Sabarnurdin, M.Sc.

2011 | Tesis | S2 Ilmu Kehutanan

Agroforestri berbasis bambu cocok untuk tanah-tanah miskin hara. Karakteristik bambu dan pertumbuhan kanopinya yang cepat mampu meningkatkan penutupan tanah, memperbaiki ketersediaan unsur hara dan lengas tanah serta mencegah terjadinya erosi dengan mengurangi limpasan permukaan. Penelitian bertujuan mengetahui faktor-faktor yang memberikan pengaruh terhadap limpasan permukaan dan ketersediaan bahan organik tanah (BOT) pada agroforestri berbasis bambu di Kabupaten Lombok Timur. Waktu penelitian Maret 2010 s.d. Maret 2011 di Desa Lenek Daya, Kecamatan Aikmel, Kabupaten Lombok Timur. Plot penelitian berada pada rentang kelerengan: 0-15 o ; 30-45 o ; dan 45-65 o , dengan penutupan bambu: 0-25%; 25-50%; 50-75% dan lebih dari 75%. Plot penelitian berukuran 4x12 m sebanyak 12 plot. Pengukuran meliputi: limpasan permukaan, penutupan bambu, curah hujan, sedimen terlarut, sifat fisik dan kimia tanah serta BOT. Data dianalisis melalui uji korelasi dan regresi. Hasil uji regresi menunjukan adanya perubahan limpasan permukaan yang dipengaruhi oleh perubahan penutupan kanopi bambu, lama hujan, intensitas hujan dan fraksi pasir tanah. Berdasarkan uji regresi tersebut, lama hujan merupakan variabel yang memberikan pengaruh tertinggi, sedangkan penutupan tajuk bambu secara signifikan memberikan pengaruh terhadap penurunan limpasan permukaan. Penutupan bambu tidak menunjukkan hubungan dengan peningkatan BOT namun menunjukkan korelasi dengan peningkatan kapasitas tukar kation (KTK) tanah. Dampak positif penutupan bambu terhadap lahan maupun terhadap peningkatan pendapatan petani ditentukan oleh intensitas pengelolaan yang dilakukan. Peningkatan kesuburan tanah pasir ditentukan oleh peningkatan BOT yang meningkatkan KTK tanah, dan oleh penurunan fraksi pasir yang menurunkan kehilangan unsur P akibat pencucian hara.

Bamboo-based agroforestry is suitable for poor-nutrient soil. The characteristics of bamboo and the rapid growth of its canopy can improve soil cover, nutrient availability and soil moisture and prevent erosion by reducing surface runoff. The research was aimed at determining the factors that influenced the availability of surface runoff and soil organic matter (SOM) on the bamboo-based agroforestry in Lombok Timur. The research was done from March 2010 until March 2011 in Lenek Daya village, Aikmel sub-district, Lombok Timur district. The research plots were located on slopes range: 0-15 o , 30-45 o , and 45-65 o ; with the bamboo canopy closure: 0-25%, 25-50%, 50-75% and over 75%. The study site was set of 12 research plots, each 4 m by 12 m. The measurements included surface runoff, bamboo canopy closure, rainfall, dissolved sediment, soil physical and chemical properties as well as SOM. Correlation and regression tests were used in data analysis. The results of the regression tests showed a change in surface runoff which was influenced by the changes in bamboo canopy closure, rain duration, rain intensity and soil sand fraction. Based on the regression tests, the rain duration was the highest influencing variable, whereas the bamboo canopy closure significantly decreased surface runoff. Bamboo closure had no correlation to the increase of SOM but had some correlation to the increase of soil cation exchange capacity (CEC). The positive impact of bamboo closure to the land and to the increase of farmers' income was determined by land management intensity. The increase of sand soil fertility was determined by both the increase of SOM which increased soil CEC and the decrease of sand fraction which decreased phosphorus element loss due to nutrient leaching.

Kata Kunci : agroforestri, bambu, limpasan permukaan, bahan organik tanah