Changes in soil organic carbon stocks after conversion from forest to oil palm plantations in Malaysian Borneo

Abstract

The continuous rise in the global demand for palm oil has resulted in large-scale expansion of industrial oil palm plantations-largely at the expense of primary and secondary forests. The potentially negative environmental impacts of these conversions have given rise to closer scrutiny. However, empirical data on the effects of conversion of forests to industrial oil palm plantations on soil organic carbon (SOC) stocks is scarce and patchy. We evaluated the changes in SOC stocks after conversion of tropical forest into oil palm plantations over the first and second rotation period in Sarawak, Malaysian Borneo. Soil samples were collected from three age classes of oil palm plantations converted from forest (49, 39 and 29 years ago respectively) with three replicate sites and four adjacent primary forest sites as reference. In each site under oil palm, the three management zones, namely weeded circle (WC), frond stacks (FS), and between palm (BP), were sampled separately. All soil samples were collected from five soil layers (0-5, 5-15, 15-30, 30-50 and 50-70 cm). Samples were analysed for SOC concentration, soil bulk density, pH and soil texture. Results showed SOC stocks declined by 42%, 24% and 18% after 29, 39 and 49 years of conversion respectively. Significant differences in SOC stocks were found among different management zones in the oil palm plantations, and the trend was similar for all age classes: FS>WC>BP, demonstrating the necessity of considering within-plantation variability when assessing soil C stocks. The largest differences between SOC stocks of the reference forest and converted plantations were found in the topsoil (0-15 cm depth) but differences were also found in the subsoil (>30 cm). Our results will contribute towards future modelling and life cycle accounting to calculate the carbon debt from the conversion of forest to oil palm plantations.

Measured greenhouse gas budgets challenge emission savings from palm-oil biodiesel

“…However, further measurements of emissions from second-rotation-cycle oil palm plantations or plantations on degraded lands are needed to confirm and more accurately quantify their GHG emission savings potential. A recent study, e.g., suggests that soil organic carbon stocks, after a large decrease following forest conversion to oil palm, can be partially restored by adequate management practices 61 .…”

C-organik Tanah di Perkebunan Kelapa Sawit Sumatera Utara: Status dan Hubungan dengan Beberapa Sifat Kimia Tanah

“…Di perkebunan kelapa sawit, degradasi kandungan Corganik tanah juga telah dilaporkan sebelumnya, umumnya terjadi pada awal penanaman. Namun, melalui penerapan kultur teknis yang tepat, nilai C-organik cenderung meningkat seiring pertambahan umur tanaman (Haron et al 1998;Khasanah et al 2015;Wisdom et al 2017;Rahman et al 2018).…”

“…Meskipun terjadi penurunan, namun status C-organik tetap mampu dipertahankan dalam status rendah hingga sedang (<1,75%) yang diduga karena rentang waktu pengambilan sampel yang relatif pendek (5 tahun). Hal ini, berbeda dengan hasil penelitian (Rahman et al 2018) yang menunjukkan bahwa pada 49 tahun pasca alih guna lahan, kandungan C-organik perkebunan kelapa sawit meningkat hingga 26% dari 20 tahun sebelumnya. Selain itu, kajian Haron et al (1998) juga mengatakan bahwa penambahan nilai C-organik tanah diketahui meningkat seiring pertambahan umur tanaman dari 0,82% pada umur 5 tahun menjadi 2,21% setelah berumur 20 tahun.…”

Drivers of soil carbon stabilization in oil palm plantations

“…For example, soil C inputs decrease up to 90% when rainforests are converted to oil palm plantations, resulting in a rapid drop of SOC (Guillaume et al, 2018). Soil organic C losses are not, however, uniform within plantations, and specific management zones within the plantation may even exhibit a gain in SOC (Khasanah, van Noordwijk, Ningsih, & Rahayu, 2015;Rahman et al, 2018). Soil C inputs in mature oil palm plantations without cover crops (the most common practice) occurs mostly belowground through rhizodeposition because the understorey is frequently cleared.…”