Perubahan Sifat Kimia Tanah Gambut Akibat Kebakaran Hutan dan Lahan

Abstract

Kebakaran hutan dan lahan sering terjadi di lahan gambut terutama pada tahun-tahun dengan musim kering ekstrem (El Nino). Kebakaran di lahan gambut dianggap menghilangkan fungsi ekologis lahan gambut sebagai penyimpan cadangan karbon dan dikaitkan dengan usaha menaikkan kandungan unsur hara tanah. Penelitian dilaksanakan bulan November 2022 hingga bulan Agustus 2023. Pengambilan sampel tanah dilakukan di area lahan gambut milik PT. Rimba Hutani Mas (RHM) Kecamatan Bayung Lencir, Kabupaten Musi Banyuasin Provinsi Sumatera Selatan dengan dua kondisi lahan yang berbeda, yaitu kondisi lahan terbakar dan tidak terbakar. Sampel tanah terbakar diambil di kawasan konservasi Greenbelt yang terbakar berulang pada tahun 2018, 2019 dan 2021. Sedangkan sampel tanah tidak terbakar diambil di kawasan lahan gambut budidaya tanaman Akasia (Acacia Mangium) dan Eukaliptus (Eucalyptus Myrtaceae). Sampel tanah diambil pada empat kedalaman berbeda meliputi kedalaman 0-5 cm, 5-10 cm, 10-15 cm dan 15-20 cm. Tujuan perbedaan kedalaman pengambilan sampel tersebut untuk melihat perbedaan dampak kebakaran pada masing-masing lapisan tanah. Dari dua kondisi lahan tersebut, diambil tiga titik sampel tanah secara komposit yaitu dengan mencampur tanah dari lima sub titik berbeda menurut kedalaman masing-masing dengan berat ± 1 kg. Pengambilan sampel tanah dengan metode komposit memungkinkan memperoleh sampel tanah yang benar-benar mewakili sifat kimia secara merata. Total sampel tanah yang dianalisis berjumlah 24 sampel. Analisis sifat kimia tanah dilakukan di Laboratorium Pengembangan Sumberdaya Fisik Lahan IPB. Parameter yang diamati meliputi pH, EC, kadar abu, C-organik, N-total, P-tersedia, kalium (K), natrium (Na), kalsium (Ca), magnesium (Mg), besi (Fe), mangan (Mn), tembaga (Cu), dan seng (Zn). Penilaian hasil analisis sifat kimia tanah menggunakan kriteria penilaian hasil analisis tanah. Penerapan sistem kanal tertutup mempertahankan muka air di lahan gambut sehingga gambut tidak mudah kering dan terbakar. Berdasarkan hasil penelitian, sifat kimia tanah gambut terbakar dan tidak terbakar dengan parameter pH, C-organik, N-total, K, Na, Ca, Mg, Fe, Mn, Cu, Zn tidak menunjukkan perbedaan kelas evaluasi sifat kimia tanah. Perbedaan kelas terdapat pada kandungan P-tersedia dengan rata-rata kandungan masing-masing 8,21 ppm dan 7,88 ppm dengan kelas hasil evaluasi sifat kimia tanah berturut-turut berada pada kelas sedang dan rendah yang menunjukkan persebaran mineral P2O5 dari abu mineral oksidasi bahan organik. Kebakaran meningkatkan rata-rata kandungan unsur hara dipicu persebaran mineral anorganik pasca kejadian kebakaran akibat oksidasi bahan organik. Kebakaran tidak memengaruhi sifat kimia tanah gambut. Peningkatan rata-rata kandungan unsur hara tidak disertai kenaikan kelas ketersediaan hara tanah sehingga kebakaran tidak bermanfaat menaikkan kesuburan bagi lahan gambut.

Forest and land fires often occur on peatlands, especially during years with extreme dry seasons (El Nino). Fires on peatlands are considered to disrupt the ecological function of peatlands as carbon reservoirs and are associated with efforts to increase soil nutrient levels. The research was conducted from November 2022 to August 2023. Soil samples were taken from the peatland areas owned by PT. Rimba Hutani Mas (RHM) in the Bayung Lencir District, Musi Banyuasin Regency, South Sumatra Province, under two different conditions: burned and unburned. Burned soil samples were taken from the Greenbelt conservation area that experienced repeated fires in 2018, 2019, and 2021. Unburned soil samples were collected from areas where Acacia (Acacia Mangium) and Eucalyptus (Eucalyptus Myrtaceae) were cultivated. Soil samples were collected at four different depths: 0-5 cm, 5-10 cm, 10-15 cm, and 15-20 cm. The varying depths of sample collection aimed to assess the impact of fires on each soil layer. For both conditions, three composite soil samples were collected by mixing soil from five different sub-points according to depth, with an approximate weight of 1 kg. Composite soil sampling allowed for obtaining soil samples that represented the chemical properties of the soil. A total of 24 soil samples were analyzed. Soil chemical property analysis was carried out at the Physical Land Resources Development Laboratory of IPB. The observed parameters included pH, electrical conductivity (EC), ash content, organic carbon (Organic-C), total nitrogen (Total-N), available phosphorus (Available-P), potassium (K), sodium (Na), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn). The assessment of the soil chemical properties analysis results was done using the criteria. The implementation of a closed canal system maintained the water level in the peatland, preventing it from drying out and catching fire. Based on the research results, the chemical properties of burned and unburned peat soil did not show significant differences in pH, C-organic, N-total, K, Na, Ca, Mg, Fe, Mn, Cu, and Zn. However, there was a difference in the available phosphorus content, with average values of 8.21 ppm and 7.88 ppm, resulting in moderate and low classifications. This indicated the dispersion of P2O5 minerals from the oxidation of organic matter. The fires increased the average nutrient content due to the dispersion of inorganic minerals after the fire incident, which did not affect the chemical properties of the peat soil. The increased nutrient content did not lead to an improvement in soil fertility, suggesting that fires did not contribute to enhancing the fertility of the peatland.