Abstract
Nitrogen (N) fertilization is one of the most effective practices to increase productivity, and has therefore had a fast global increase. Consequently, the effects of the application of N fertilizer on emissions of N2O have been widely studied, but the effect of rice planting on N2O emission was not adequately quantified. To evaluate the effect of rice cultivation on N2O emissions, different levels of N were applied in a typical temperate rice field, and the N2O fluxes were compared in rice-planted and non-planted soils. Seasonal N2O fluxes responded differently with respect to N fertilization in the two different soil conditions. In non-planted soils, seasonal N2O fluxes ranged within 0.31–0.34 kg N2O ha−1 under 0 kg N ha−1 fertilization, and significantly increased by increasing N fertilization rates, with an average rate of 0.0024 kg N2O kg−1 N for 3 years. In rice-planted soils, seasonal N2O fluxes were also increased by N fertilization but showed large negative N2O fluxes, irrespective of the N fertilization level. This study confirms that the rice reacted as a reducer of N2O emissions, not an emission source, in paddy fields, suggesting that N2O fluxes should be estimated by the static chamber planted with rice to obtain a more precise field environment. The differences of N2O fluxes between the rice-planted and non-planted soils might have been caused by the rice plant’s rhizospheric activities, which may have influenced the N2O consumption potential in the rice plants’ rhizosphere. The N2O consumption potential was significantly increased with increasing N fertilization rates and was highly correlated with rice biomass yields. Therefore, the decrease in N2O fluxes by N fertilization in rice-planted soils might have been caused by a decreasing denitrification potential in paddy soils.
Highlights
Nitrous oxide is a long-lived trace gas in the atmosphere and has a 298 times higher global warming potential (GWP) than equivalent amount of carbon dioxide (CO2) [1]
Irrespective of chamber installation conditions, seasonal N2O fluxes significantly increased with increasing N fertilizer application (Figure 3)
We confirmed a big difference of seasonal N2O fluxes between rice-planted and non-planted chambers under the same N fertilization levels (Figure 3)
Summary
Nitrous oxide is a long-lived trace gas in the atmosphere and has a 298 times higher global warming potential (GWP) than equivalent amount of carbon dioxide (CO2) [1]. N2O has become the most important substance contributing to ozone (O3) layer depletion after chlorofluorocarbons [2]. The atmospheric concentration of N2O has significantly increased from 270 ppbv at the pre-industrial era to 322.5 ppbv in the year 2009, with an average increase of 0.77 ppbv year−1 for the period 2000–2009 [3], mainly due to agricultural activity. The N2O emissions are mainly produced by the chemical and organic N inputs [1]. The N2O emissions are predicted to increase nearly 35–60% by the end of 2030 to meet the increasing global food demand [5]
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