Transformation of Lowland Rainforest into Oil-palm Plantations and use of Fire alter Topsoil and Litter Silicon Pools and Fluxes

Abstract

The effects of land use and fire on ecosystem silicon (Si) cycling has been largely disregarded so far. We investigated the impacts of land use and fire on Si release from topsoils and litter of lowland rainforest and oil-palm plantations in Jambi Province, Indonesia. Lower concentrations of Si in amorphous silica (ASi) were found in oil-palm plantation topsoils (2.8 ± 0.7 mg g− 1) compared to rainforest (3.5 ± 0.8 mg g− 1). Higher total Si concentrations were detected in litter from oil-palm frond piles (22.8 ± 4.6 mg g− 1) compared to rainforest litter (12.7 ± 2.2 mg g− 1). To test the impact of fire, materials were burned at 300 °C and 500 °C and were shaken with untreated samples in simulated rainwater for 28 h. Untreated oil-palm topsoils showed a significantly lower Si release (p≤ 0.05) compared to rainforest. The fire treatments resulted in an increased Si release into simulated rainwater. Si release from oil-palm topsoils and litter increased by a factor of 6 and 9 (500 °C), respectively, and Si release from rainforest topsoils and litter by a factor of 3 and 9 (500 °C). Differences between land use were related to initial ASi and litter Si concentrations, and to losses of soil organic matter during burning. We conclude that transformation of rainforest into oil palm plantations could be an important and immediate Si source after a fire event but may indirectly lead to a decrease in the long-term Si availability to plants.

Oil-palm and Rainforest Phytoliths Dissolve at Different Rates - with Implications for Silicon Cycling After Transformation of Rainforest Into Oil-palm Plantation

“…In batch experiments, larger quantities of Si were released by oil-palm litter (44 ± 12 µg Si g −1 litter) compared to rainforest litter (32 ± 8 µg Si g −1 litter) after 28 h of continuous shaking. This was due to higher Si concentrations in the oil-palm litter (23 ± 5 mg g −1 , in rainforest litter: 13 ± 2 mg g −1 ) [20].…”

“…In the plant, they detected increasing Si concentrations with oil-palm frond age, indicating Si accumulation over time and immobile behaviour of Si [22]. Von der Lühe et al (2020) [20] found trends of decreasing amorphous silica (ASi, which mainly consists of BSi in topsoils) in topsoils when lowland rainforests were converted to oilpalm plantations on Sumatra, Indonesia. In batch experiments, larger quantities of Si were released by oil-palm litter (44 ± 12 µg Si g −1 litter) compared to rainforest litter (32 ± 8 µg Si g −1 litter) after 28 h of continuous shaking.…”

“…Transforming tropical rainforests into arable land may result in reduced Si supply to crops, especially, in soils that are strongly desilicated, thus having low levels of plant-available Si [15,16]. In the long-term, LULC change may lead to increased losses of BSi from the soil system due to accelerated Si leaching, harvest and topsoil erosion [17][18][19][20].…”

Estimating oil-palm Si storage, Si return to soils and Si losses through harvest in smallholder oil-palm plantations of Sumatra, Indonesia

“…Oil-palm plantations are usually cultivated for about 25 years (Corley and Tinker, 2016) after which the oil-palm stem is considered a waste product (Awalludin et al, 2015;Onoja et al, 2019). It used to be common practice to 350 burn the stem, as the ash was regarded to sustain soil fertility (Selamat et al, 2019) by releasing Si and other nutrients into topsoil (von der Lühe et al, 2020;Selamat et al, 2019). Yet, these nutrients, including Si, are released from the ash in such high amounts and so quickly that they are highly susceptible to leaching.…”

“…It is likely that many nutrients are lost from the system before a new generation of oil palms can take them up. Thus, despite the shortterm fertilizing effect of the ash, this process may enhance nutrient and Si depletion for the long term (von der 355 Lühe et al, 2020). Nowadays, replanting follows a zero-burning policy (Corley and Tinker, 2016) to reduce greenhouse gas emissions, air pollution, and to prevent fires from getting out of control and impacting natural vegetation.…”