Soil nitrogen oxide fluxes from lowland forests converted to smallholder rubber and oil palm plantations in Sumatra, Indonesia

Abstract

Abstract. Oil palm (Elaeis guineensis) and rubber (Hevea brasiliensis) plantations cover large areas of former rainforest in Sumatra, Indonesia, supplying the global demand for these crops. Although forest conversion is known to influence soil nitrous oxide (N 2 O) and nitric oxide (NO) fluxes, measurements from oil palm and rubber plantations are scarce (for N 2 O) or nonexistent (for NO). Our study aimed to (1) quantify changes in soil-atmosphere fluxes of N oxides with forest conversion to rubber and oil palm plantations and (2) determine their controlling factors. In Jambi, Sumatra, we selected two landscapes that mainly differed in texture but were both on heavily weathered soils: loam and clay Acrisol soils. Within each landscape, we investigated lowland forests, rubber trees interspersed in secondary forest (termed as "jungle rubber"), both as reference land uses and smallholder rubber and oil palm plantations as converted land uses. In the loam Acrisol landscape, we conducted a followon study in a large-scale oil palm plantation (called PTPN VI) for comparison of soil N 2 O fluxes with smallholder oil palm plantations. Land-use conversion to smallholder plantations had no effect on soil N-oxide fluxes (P = 0.58 to 0.76) due to the generally low soil N availability in the reference land uses that further decreased with land-use conversion. Soil N 2 O fluxes from the large-scale oil palm plantation did not differ with those from smallholder plantations (P = 0.15). Over 1-year measurements, the temporal patterns of soil N-oxide fluxes were influenced by soil mineral N and water contents. Across landscapes, annual soil N 2 O emissions were controlled by gross nitrification and sand content, which also suggest the influence of soil N and water availability. Soil N 2 O fluxes (µg N m −2 h −1 ) were 7 ± 2 to 14 ± 7 (reference land uses), 6 ± 3 to 9 ± 2 (rubber), 12 ± 3 to 12 ± 6 (smallholder oil palm) and 42 ± 24 (large-scale oil palm). Soil NO fluxes (µg N m −2 h −1 ) were −0.6 ± 0.7 to 5.7 ± 5.8 (reference land uses), −1.2 ± 0.5 to −1.0 ± 0.2 (rubber) and −0.2 ± 1.2 to 0.7 ± 0.7 (smallholder oil palm). To improve the estimate of soil N-oxide fluxes from oil palm plantations in this region, studies should focus on large-scale plantations (which usually have 2 to 4 times higher N fertilization rates than smallholders) with frequent measurements following fertilizer application.

Minimum forest cover required for sustainable water flow regulation of a watershed: a case study in Jambi Province, Indonesia

“…Although oil palm is of economic value to farmers and the local regions in which it is grown, it has received environmental and social criticism, often being held responsible for deforestation (Wicke et al, 2011;Vijay et al, 2016;Gatto et al, 2017), biodiversity loss (Fitzherbert et al, 2008;Koh and Wilcove, 2008;Wilcove and Koh, 2010;Carlson et al, 2012;Krashevska et al, 2015), decreased soil carbon stocks (Guillaume et al, 2015Pransiska et al, 2016), and increased greenhouse gas emissions (Allen et al, 2015;Hassler et al, 2017). Similarly, rubber plantations have environmental impacts such as reducing the soil infiltration capacity, accelerating soil erosion, increasing stream sediment loads (Ziegler et al, 2009;Tarigan et al, 2016b), and decreasing soil carbon stocks (Ziegler et al, 2011).…”

“…Functional water flow regulation by a watershed reduces flood peaks by moderating direct runoff (Le Maitre et al, 2014;Ellison et al, 2017) via soil water infiltration through the soil surface and percolation through the soil profile. This vertical movement of water through the soil determines how much water flows as direct runoffs and how much reaches the water table where it is sustained as baseflow or groundwater (Hewlett and Hibbert, 1967;Bruijnzeel, 1990;Le Maitre et al, 2014;Tarigan et al, 2016b). Forest vegetation provides organic matter and habitat for soil organisms, thereby facilitating higher levels of infiltration than other land uses (Hewlett and Hibbert, 1967).…”

“…This vertical movement of water through the soil determines how much water flows as direct runoffs and how much reaches the water table where it is sustained as baseflow or groundwater (Hewlett and Hibbert, 1967;Bruijnzeel, 1990;Le Maitre et al, 2014;Tarigan et al, 2016b). Forest vegetation provides organic matter and habitat for soil organisms, thereby facilitating higher levels of infiltration than other land uses (Hewlett and Hibbert, 1967).…”

Substantial N 2 O emissions from peat decomposition and N fertilization in an oil palm plantation exacerbated by hotspots

“…Nitrous oxide is a gaseous intermediate in the reaction sequence of denitrification and a by-product of nitrification that leaks from microbial cells into the soil and ultimately to the atmosphere (Bouwman 1998, Smith et al 2003 (Melling et al 2007, Aini et al 2015, Sakata et al 2015, Hassler et al 2017 and some are based on very short sampling periods (Ishizuka et al 2005, Banabas 2007, Fowler et al 2011. Aini et al (2015) observed highly elevated emission rates following N fertilization in a plantation cultivated on mineral soil in Jambi, Sumatra.…”

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

“…Conversion of forests to agricultural plantations may further contribute substantially to non-CO 2 GHG emissions 19 , but field quantifications of methane (CH 4 , global warming potential, GWP of 25 2,20 ) and nitrous oxide (N 2 O, GWP of 298 2,20 ) emissions in oil palm plantations are so far limited [16][17][18]21,22 . The net global warming potential (GWP net ) 23 , which includes the net ecosystem exchange (NEE) of CO 2 fluxes as well as soil CH 4 and N 2 O fluxes, has previously not been assessed for oil palm plantations, despite their rapid expansion across the tropics.…”