Abstract
Abstract. Traditional land management (no tillage, no drainage, NTND) during the winter fallow season results in substantial CH4 and N2O emissions from double-rice fields in China. A field experiment was conducted to investigate the effects of drainage and tillage during the winter fallow season on CH4 and N2O emissions and to develop mitigation options. The experiment had four treatments: NTND, NTD (drainage but no tillage), TND (tillage but no drainage), and TD (both drainage and tillage). The study was conducted from 2010 to 2014 in a Chinese double-rice field. During winter, total precipitation and mean daily temperature significantly affected CH4 emission. Compared to NTND, drainage and tillage decreased annual CH4 emissions in early- and late-rice seasons by 54 and 33 kg CH4 ha−1 yr−1, respectively. Drainage and tillage increased N2O emissions in the winter fallow season but reduced it in early- and late-rice seasons, resulting in no annual change in N2O emission. Global warming potentials of CH4 and N2O emissions were decreased by 1.49 and 0.92 t CO2 eq. ha−1 yr−1, respectively, and were reduced more by combining drainage with tillage, providing a mitigation potential of 1.96 t CO2 eq. ha−1 yr−1. A low total C content and high C / N ratio in rice residues showed that tillage in the winter fallow season reduced CH4 and N2O emissions in both early- and late-rice seasons. Drainage and tillage significantly decreased the abundance of methanogens in paddy soil, and this may explain the decrease of CH4 emissions. Greenhouse gas intensity was significantly decreased by drainage and tillage separately, and the reduction was greater by combining drainage with tillage, resulting in a reduction of 0.17 t CO2 eq. t−1. The results indicate that drainage combined with tillage during the winter fallow season is an effective strategy for mitigating greenhouse gas releases from double-rice fields.
Highlights
Methane (CH4) and nitrous oxide (N2O) are important greenhouse gases (GHGs)
Differences in seasonal CH4 and N2O emissions, 100-year global warming potentials (GWPs) (CH4 and N2O), and grain yields among treatments were analyzed with a repeated-measures one-way analysis of variance (ANOVA) and least significant differences (LSD) test
An occasional negative CH4 flux was observed over the four winter fallow seasons (Fig. 1), the double-rice field in this study was an entire source of CH4 emission, in particular during the 2011–2012 winter fallow season (Table 1)
Summary
Methane (CH4) and nitrous oxide (N2O) are important greenhouse gases (GHGs). According to the Greenhouse Gas Bulletin of World Meteorological Organization, the concentrations of atmospheric CH4 and N2O reached 1833 and 327 ppb in 2014, respectively (WMO, 2015). Since the overall balance between the net exchange of CH4 and N2O emissions constitutes the global warming potentials (GWPs) of the rice ecosystem, the effects of soil drainage in the winter fallow season on mitigating the yearly GWPs from doublerice fields are unclear. It is beneficial for rainwater to penetrate into the subsoil because this minimizes rainwater accumulation in winter Tillage makes it difficult to establish a strict anaerobic environment in the top soil, which would directly reduce CH4 emissions during the non-rice growing season and indirectly inhibit CH4 emissions during the following rice season. A possible mitigating strategy that includes crop residues plowed into the soil along with drainage in the winter fallow season has been proposed for a double-rice field (Shang et al, 2011). The mitigation potential of drainage combined with tillage in the winter fallow season on annual CH4 and N2O emissions from double-rice fields remains unclear. The objectives were to (1) investigate the effects of soil drainage and tillage during the winter fallow season on CH4 and N2O emissions, (2) estimate the mitigation potential of drainage and tillage, and (3) suggest optimal land management strategies during the winter fallow season for reducing GWPs of CH4 and N2O emissions
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