The Changes of Carbon Stocks on Rejuvenation of Smallholder Rubber Plantation

Abstract
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Rejuvenation of rubber tree (Hevea brasiliensis) can lead to a reduction of carbon stocks. Therefore, appropriate methods are needed to minimize such losses. The objective of this study was to analyze the changes on carbon stocks in the rejuvenation of rubber with logging system of 30%, 50%, 70%, and 100% and intercrops between the young rubber plantation (maize and peanuts). The research was conducted from January to December 2013 at smallholder rubber plantation in Way Tuba District, Way Kanan Regency, Lampung when the trees were 25 years old. The design used was a randomized block design with three replications. The tested treatments were logging of old rubber plants at 30%, 50%, 70%, and 100%, which then followed by planting of young rubber plants and intercropped (maize and peanut). The variables measured were: (1) fresh weight and dry weight (biomass); (2) fixed carbon content; and (3) carbon stocks on rubber plantation, maize, peanuts, and young rubber plants. The results showed that rubber logging at about 30%–100% could reduce carbon stocks by 7.4–24.29 ton C/ha. However, planting of young rubber plants as well as intercropped (maize and peanut) may contributed to the carbon enrichment up to 0.98-3.28 ton C/ha. Hence, the loss of carbon due to logging system turn out to be 6.29–22.92 ton C/ha.
Peremajaan tanaman karet (Hevea brasiliensis) memberikan konsekuensi menurunnya cadangan karbon sehingga diperlukan teknik untuk meminimalisasi kehilangan tersebut. Penelitian bertujuan menganalisis perubahan cadangan karbon pada penebangan tanaman karet tua sebanyak 30%, 50%, 70%, dan 100% yang diikuti oleh penanaman karet muda dengan tanaman sela (jagung dan kacang tanah). Penelitian dilaksanakan bulan Januari sampai Desember 2013 pada pertanaman karet rakyat umur 25 tahun di Kecamatan Way Tuba, Kabupaten Way Kanan, Lampung. Rancangan yang digunakan adalah acak kelompok dengan tiga ulangan. Perlakuan yang diuji adalah penebangan tanaman karet tua 30%, 50%, 70%, dan 100% yang masing-masing diikuti dengan penanaman karet muda dan tanaman sela (jagung dan kacang tanah). Variabel yang diamati: (1) bobot segar dan kering (biomassa); (2) kandungan karbon terikat (fixed carbon); dan (3) cadangan karbon pada pertanaman karet, jagung, kacang tanah, dan tanaman karet muda. Hasil penelitian menunjukkan penebangan karet sebanyak 30%–100% dari populasi menurunkan cadangan karbon sebesar 7,4–24,29 ton C/ha. Penanaman karet muda dan tanaman sela (jagung dan kacang tanah) dapat berkontribusi terhadap penambahan karbon sebesar 0,98-3,28 ton C/ha sehingga kehilangan karbon akibat penebangan tanaman karet tua berkurang menjadi 6,29–22,92 ton C/ha.
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