DISTRIBUSI SPASIAL KEHILANGAN TANAH DAN KEHILANGAN KARBON ORGANIK TANAH OLEH ALIRAN PERMUKAAN DI DAS OYO

ADITYA PANDU WICAKSONO, S.SI., Dr. Eko Haryono, M.Si.

2012 | Tesis | S2 Ilmu Lingkungan

Proses kehilangan tanah oleh aliran permukaan selalu akan disertai oleh kehilangan karbon organik tanah. Kehilangan karbon organik tanah menyebabkan terganggunya sirkulasi karbon global dan dapat mempengaruhi tingkat kesuburan tanah. Penelitian ini dilakukan untuk mengkaji distribusi spasial kehilangan tanah dan kehilangan karbon organic tanah dan mengkaji faktor yang paling berpengaruh terhadap kehilangan tanah diantaranya faktor lereng, erodibilitas tanah, dan manajemen konservasi lahan yang dipicu oleh erosivitas hujan. Distribusi spasial potensi kehilangan tanah dan kehilangan karbon organik tanah yang terjadi pada 13 Sub DAS di DAS Oyo juga perlu diketahui agar upaya konservasi lahan dapat dilakukan secara efisien. Penelitian ini menggunakan kombinasi antara metode USPED dan metode Staar. Hasil perhitungan USPED digunakan dalam perhitungan metode Staar untuk mengetahui kehilangan karbon organik di perairan. Validasi kehilangan tanah dilakukan dengan memanfaatkan hasil perhitungan kehilangan tanah aktual. Validasi total kehilangan karbon organik yang terdapat di perairan dilakukan dengan perhitungan rating curve kandungan karbon organic yang terdapat di dalam sampel suspensi sedimen. Faktor kehilangan tanah yang paling berpengaruh dapat diketahui menggunakan analisis sensitivitas. Hasil perhitungan kehilangan tanah menggunakan USPED mendekati nilai kehilangan tanah aktual yang ditunjukkan dengan nilai akurasi sebesar 89%. Sub DAS Munggur merupakan Sub DAS yang paling banyak mengalami kehilangan tanah sebesar 5289.3 ton/thn dan kehilangan karbon organik tanah sebesar 165,79 ton/thn sehingga menjadi prioritas dalam konservasi lahan. Total kehilangan tanah di seluruh DAS Oyo sebesar 4207.9 ton/thn dan total kehilangan karbon organik sebesar 255.89 ton/thn dari total kandungan karbon organik sebesar 522,44 ton/thn. Persentase kehilangan karbon organik tanah setiap tahunnya mencapai 48,98 % dari total kandungan karbon organik yang terdapat di DAS Oyo. Faktor konservasi dan pengelolaan tanaman merupakan faktor yang paling berpengaruh jika dibandingkan dengan factor lereng dan erodibilitas tanah terhadap kehilangan tanah dan kehilangan karbon organik tanah di DAS Oyo. Nilai sensitivitas yang dilakukan di Sub DAS Munggur sebesar 0,2 yang merupakan nilai yang paling besar daripada faktor yang lain.

Soil loss process is always followed by the loss of soil organic carbon. As the consequence, there is a disturbance on the global carbon cycle and on the soil fertility condition. This research aimed to assess the spatial distribution of soil and soil organic carbon loss and also to identify the most affecting factors of soil loss such as slope, rain erosivity, soil erodibility, and land conservation, and crop management. Spatial distribution of the soil and organic loss potential is essential to be identified in order to determine the efficient land conservation. The research was conducted in 13 sub-watershed of Oyo Watershed. The research combined USPED and Staar methods to obtain reliable soil and organic carbon loss estimation. The Staar method was used to estimate the soil carbon loss suspended in the river. The USPED soil loss estimation was validated by the actual soil loss which was measured from erosion features found in the research area. Whereas, total soil organic carbon loss was validated with rating curve of organic carbon contained in the sediment suspension. The most affecting factor of soil loss was defined by using sensitivity analysis. The USPED soil loss was estimated to approximate the actual soil loss and was proved by 89% of accuracy level. Munggur sub-watershed experienced the highest soil loss by 5289.3 tons/year and soil organic loss by 165.79 tons/year. Whereas, soil loss in the entire Oyo watershed was estimated at 4207.9 tons/year followed by 2555.89 tons/year of soil organic loss. The soil loss which takes place in Oyo Watershed has depleted the soil organic up to 48.98%. The research found out that conservation and crop management was the most affecting factor to soil loss. Sensitivity analysis conducted for Munggur Sub-watershed has shown that the value of land conservation and crop management was 0.2 higher than the other two factors, i.e. slope and soil erodibility. It was concluded that land conservation and crop management was the most affecting factors for the soil and soil organic carbon loss.

Kata Kunci : kehilangan tanah, karbon organik, USPED, konservasi dan pengelolaan tanaman.