Effects of Long-Term Nitrogen Fertilization and Ground Water Level Changes on Soil CO2 Fluxes from Oil Palm Plantation on Tropical Peatland

Ryusuke Hatano,Kah Joo Goh,Auldry Chaddy,Kiwamu Ishikura,Yo Toma,Lulie Melling

doi:10.3390/atmos12101340

Ryusuke Hatano, Kah Joo Goh + Show 4 more

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https://doi.org/10.3390/atmos12101340

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Abstract

A long-term study on the effect of nitrogen (N) fertilization on soil carbon dioxide (CO2) fluxes in tropical peatland was conducted to (1) quantify the annual CO2 emissions from an oil palm plantation under different N application rates and (2) evaluate the temporal effects of groundwater level (GWL) and water-filled pore space (WFPS) on soil organic carbon (SOC) and CO2 fluxes. Monthly measurement of soil CO2 fluxes using a closed chamber method was carried out from January 2010 until December 2013 and from January 2016 to December 2017 in an oil palm plantation on tropical peat in Sarawak, Malaysia. Besides the control (T1, without N fertilization), there were three N treatments: low N (T2, 31.1 kg N ha−1 year−1), moderate N (T3, 62.2 kg N ha−1 year−1), and high N (T4, 124.3 kg N ha−1 year−1). The annual CO2 emissions ranged from 7.7 ± 1.2 (mean ± SE) to 16.6 ± 1.0 t C ha−1 year−1, 9.8 ± 0.5 to 14.8 ± 1.4 t C ha−1 year−1, 10.5 ± 1.8 to 16.8 ± 0.6 t C ha−1 year−1, and 10.4 ± 1.8 to 17.1 ± 3.9 t C ha−1 year−1 for T1, T2, T3, and T4, respectively. Application of N fertilizer had no significant effect on annual cumulative CO2 emissions in each year (p = 0.448), which was probably due to the formation of large quantities of inorganic N when GWL was temporarily lowered from January 2010 to June 2010 (−80.9 to −103.4 cm below the peat surface), and partly due to low soil organic matter (SOM) quality. A negative relationship between GWL and CO2 fluxes (p < 0.05) and a positive relationship between GWL and WFPS (p < 0.001) were found only when the oil palm was young (2010 and 2011) (p < 0.05), indicating that lowering of GWL increased CO2 fluxes and decreased WFPS when the oil palm was young. This was possibly due to the fact that parameters such as root activity might be more predominant than GWL in governing soil respiration in older oil palm plantations when GWL was maintained near or within the rooting zone (0–50 cm). This study highlights the importance of roots and WFPS over GWL in governing soil respiration in older oil palm plantations. A proper understanding of the interaction between the direct or indirect effect of root activity on CO2 fluxes and balancing its roles in nutrient and water management strategies is critical for sustainable use of tropical peatland.

Highlights

Tropical peat swamp forests play an important role in the global carbon (C) cycle and have contributed to climate change
Higher soil CO2 fluxes ranging from 172 to 309.8 mg C m−2 hr−1 occurred when groundwater level (GWL) dropped from −80.9 to −103.4 cm below the peat surface from January to June 2010
Our study found no significant effects of N fertilization on CO2 emissions (p = 0.448) (Table 1), similar to Watanabe et al [25] and Sakata et al [26]

Summary

Introduction

Tropical peat swamp forests play an important role in the global carbon (C) cycle and have contributed to climate change. Deforestation, burning, and drainage for land conversion have significantly increased the decomposition rate of soil organic matter (SOM) in peatland [3–5], which has, in turn, caused elevated greenhouse gas (GHG) emissions, especially carbon dioxide (CO2). This has attracted global attention, especially from those concerned about climate change. Peat decomposition caused by oil palm development on tropical peatland was probably the main reason for the large source of N2O emission, as evidenced by the positive correlation between CO2 and N2O fluxes [20,21]

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