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Open AccessArticle

Soil N2O Emissions under Different N Rates in an Oil Palm Plantation on Tropical Peatland

1
Laboratory of Soil Science, Graduate School of Agriculture, Hokkaido University, Hokkaido 060-8589, Japan
2
Sarawak Tropical Peat Research Institute, Lot 6035, Kuching-Samarahan Expressway, 94300 Kota Samarahan, Sarawak, Malaysia
3
Tokachi Agricultural Experiment Station, Hokkaido Research Organization, Hokkaido 082-0081 Japan
*
Author to whom correspondence should be addressed.
Agriculture 2019, 9(10), 213; https://doi.org/10.3390/agriculture9100213
Received: 1 July 2019 / Revised: 17 September 2019 / Accepted: 19 September 2019 / Published: 1 October 2019
(This article belongs to the Special Issue Greenhouse Gas Emissions in Agroecosystems)
(1) Background: Nitrogen (N) fertilization on drained tropical peatland will likely stimulate peat decomposition and mineralization, enhancing N2O emission from the peat soil. (2) Methods: A field experiment was conducted to quantify the N2O emissions from soil in an oil palm plantation (Elaeis guineensis Jacq.) located in a tropical peatland in Sarawak, Malaysia, under different rates of N fertilizers. The study was conducted from January 2010 to December 2013 and resumed from January 2016 to December 2017. Nitrous oxide (N2O) flux was measured every month using a closed chamber method for four different N rates; control—without N (T1), 31.1 kg N ha−1 yr−1 (T2), 62.2 kg N ha−1 yr−1 (T3), and 124.3 kg N ha−1 yr−1 (T4); (3) Results: Application of the N fertilizer significantly increased annual cumulative N2O emissions for T4 only in the years 2010 (p = 0.017), 2011 (p = 0.012), 2012 (p = 0.007), and 2016 (p = 0.048). The highest average annual cumulative N2O emissions were recorded for T4 (41.5 ± 28.7 kg N ha−1 yr−1), followed by T3 (35.1 ± 25.7 kg N ha−1 yr−1), T1 (25.2 ± 17.8 kg N ha−1 yr−1), and T2 (25.1 ± 15.4 kg N ha−1 yr−1), indicating that the N rates of 62.2 kg N ha−1 yr−1 and 124.3 kg N ha−1 yr−1 increased the average annual cumulative N2O emissions by 39% and 65%, respectively, as compared to the control. The N fertilization had no significant effect on annual oil palm yield (p = 0.994). Alternating between low (deeper than −60 cm) and high groundwater level (GWL) (shallower than −60 cm) enhanced nitrification during low GWL, further supplying NO3 for denitrification in the high GWL, and contributing to higher N2O emissions in high GWL. The emissions of N2O ranged from 17 µg N m−2 hr−1 to 2447 µg N m−2 hr−1 and decreased when the water-filled pore space (WFPS) was between 70% and 96%, suggesting the occurrence of complete denitrification. A positive correlation between N2O emissions and NO3 at 70–96% WFPS indicated that denitrification increased with increased NO3 availability. Based on their standardized regression coefficients, the effect of GWL on N2O emissions increased with increased N rate (p < 0.001). Furthermore, it was found that annual oil palm yields negatively correlated with annual N2O emission and NO3 for all treatments. Both nitrification and denitrification increased with increased N availability, making both processes important sources of N2O in oil palm cultivation on tropical peatland.; and (4) Conclusions: To improve understanding of N2O mitigation strategies, further studies should consider plant N uptake on N2O emissions, at least until the completion of the planting. View Full-Text
Keywords: ground water level (GWL); water-filled pore space (WFPS); oil palm yield; nitrification; denitrification ground water level (GWL); water-filled pore space (WFPS); oil palm yield; nitrification; denitrification
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MDPI and ACS Style

Chaddy, A.; Melling, L.; Ishikura, K.; Hatano, R. Soil N2O Emissions under Different N Rates in an Oil Palm Plantation on Tropical Peatland. Agriculture 2019, 9, 213.

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