Soil fertility controls soil–atmosphere carbon dioxide and methane fluxes in a tropical landscape converted from lowland forest to rubber and oil palm plantations

Abstract

Abstract. Expansion of palm oil and rubber production, for which global demand is increasing, causes rapid deforestation in Sumatra, Indonesia, and is expected to continue in the next decades. Our study aimed to (1) quantify changes in soil CO 2 and CH 4 fluxes with land-use change and (2) determine their controlling factors. In Jambi Province, Sumatra, we selected two landscapes on heavily weathered soils that differ mainly in texture: loam and clay Acrisol soils. In each landscape, we investigated the reference land-use types (forest and secondary forest with regenerating rubber) and the converted land-use types (rubber, 7-17 years old, and oil palm plantations, 9-16 years old). We measured soil CO 2 and CH 4 fluxes monthly from December 2012 to December 2013. Annual soil CO 2 fluxes from the reference land-use types were correlated with soil fertility: low extractable phosphorus (P) coincided with high annual CO 2 fluxes from the loam Acrisol soil that had lower fertility than the clay Acrisol soil (P < 0.05). Soil CO 2 fluxes from the oil palm (107.2 to 115.7 mg C m −2 h −1 ) decreased compared to the other land-use types (between 178.7 and 195.9 mg C m −2 h −1 ; P < 0.01). Across land-use types, annual CO 2 fluxes were positively correlated with soil organic carbon (C) and negatively correlated with 15 N signatures, extractable P and base saturation. This suggests that the reduced soil CO 2 fluxes from oil palm were the result of strongly decomposed soil organic matter and reduced soil C stocks due to reduced litter input as well as being due to a possible reduction in C allocation to roots due to improved soil fertility from liming and P fertilization in these plantations. Soil CH 4 uptake in the reference landuse types was negatively correlated with net nitrogen (N) mineralization and soil mineral N, suggesting N limitation of CH 4 uptake, and positively correlated with exchangeable aluminum (Al), indicating a decrease in methanotrophic activity at high Al saturation. Reduction in soil CH 4 uptake in the converted land-use types (ranging from −3.0 to −14.9 µg C m −2 h −1 ) compared to the reference land-use types (ranging from −20.8 to −40.3 µg C m −2 h −1 ; P < 0.01) was due to a decrease in soil N availability in the converted land-use types. Our study shows for the first time that differences in soil fertility control the soil-atmosphere exchange of CO 2 and CH 4 in a tropical landscape, a mechanism that we were able to detect by conducting this study on the landscape scale.

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

“…Thus, changes in soil N-oxide fluxes can be attributed to land-use change with its associated management practices. The plantations' ages ranged between 7 and 17 years, and tree density, tree height, basal area and tree species abundance were higher in the reference land uses than the monoculture plantations (all reported by Allen et al, 2015;Hassler et al, 2015;Kotowska et al, 2015).…”

“…2.2) were conducted in 2013 (Appendix Table A1). A more detailed description of the study sites and plot design was reported earlier by Allen et al (2015) and Hassler et al (2015).…”

“…Additionally, the comparability of initial soil conditions between the reference and converted land uses was tested based on a land-use-independent soil characteristic, i.e., clay content at a 0.5-2 m depth, which did not statistically differ among land uses within each landscape (Allen et al, 2015;Hassler et al, 2015). Thus, changes in soil N-oxide fluxes can be attributed to land-use change with its associated management practices.…”

“…Management practices in the plantations included manual harvest, weeding and fertilizer application (details reported by Hassler et al, 2015). In 2013, fertilization in the smallholder oil palm plantations was conducted one to two times per year, and fertilization rates ranged between 48-88 kg N ha −1 yr −1 (except two smallholders who applied 138 kg N ha −1 yr −1 ), 21-38 kg P ha −1 yr −1 and 40-157 kg K ha −1 yr −1 , with the lower range in the clay Acrisol and the upper range in the loam Acrisol.…”

“…HIP suggests that the higher the soil N availability is, the higher the soil N-oxide fluxes are and that well-aerated soil conditions (low moisture contents) favor for nitrification with NO as the main gaseous product, while with increasing water content denitrification with increasing proportion of N 2 O prevails (Davidson et al, 2000). Although there are other factors affecting soil N 2 O and NO fluxes through their influence on nitrification and denitrification (e.g., soil pH, temperature, bioavailable carbon; Firestone and Davidson, 1989;Heinen, 2006;Skiba and Smith, 2000), landscape-scale investigations in tropical areas show the dominant role of soil N availability and water content Koehler et al, 2009;Müller et al, 2015).…”