Abstract
Abstract. To safeguard food security and preserve precious water resources, the technology of water-saving ground cover rice production system (GCRPS) is being increasingly adopted for rice cultivation. However, changes in soil water status and temperature under GCRPS may affect soil biogeochemical processes that control the biosphere–atmosphere exchanges of methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2). The overall goal of this study is to better understand how net ecosystem greenhouse gas exchanges (NEGE) and grain yields are affected by GCRPS in an annual rice-based cropping system. Our evaluation was based on measurements of the CH4 and N2O fluxes and soil heterotrophic respiration (CO2 emissions) over a complete year, and the estimated soil carbon sequestration intensity for six different fertilizer treatments for conventional paddy and GCRPS. The fertilizer treatments included urea application and no N fertilization for both conventional paddy (CUN and CNN) and GCRPS (GUN and GNN), and solely chicken manure (GCM) and combined urea and chicken manure applications (GUM) for GCRPS. Averaging across all the fertilizer treatments, GCRPS increased annual N2O emission and grain yield by 40 and 9%, respectively, and decreased annual CH4 emission by 69%, while GCRPS did not affect soil CO2 emissions relative to the conventional paddy. The annual direct emission factors of N2O were 4.01, 0.09 and 0.50% for GUN, GCM and GUM, respectively, and 1.52% for the conventional paddy (CUN). The annual soil carbon sequestration intensity under GCRPS was estimated to be an average of −1.33 Mg C ha−1 yr−1, which is approximately 44% higher than the conventional paddy. The annual NEGE were 10.80–11.02 Mg CO2-eq ha−1 yr−1 for the conventional paddy and 3.05–9.37 Mg CO2-eq ha−1 yr−1 for the GCRPS, suggesting the potential feasibility of GCRPS in reducing net greenhouse effects from rice cultivation. Using organic fertilizers for GCRPS considerably reduced annual emissions of CH4 and N2O and increased soil carbon sequestration, resulting in the lowest NEGE (3.05–5.00 Mg CO2-eq ha−1 yr−1). Accordingly, water-saving GCRPS with organic fertilizer amendments was considered the most promising management regime for simultaneously achieving relatively high grain yield and reduced net greenhouse gas emission.
Highlights
Atmospheric methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2) are key compounds in biogeochemical carbon and nitrogen cycling, thereby playing important roles for atmospheric chemistry and climate change (IPCC, 2007)
We investigated six fertilizer treatments under the two rice production systems (Table 1): two fertilizer treatments for the conventional paddy (i.e., CNN: no nitrogen fertilization as a control and CUN: urea applied at a common rate) and four fertilizer treatments in ground cover rice production system (GCRPS) (i.e., GNN: no nitrogen fertilization as a control, GUN: urea applied at a common rate, GCM: chicken manure applied at a common N rate, and GUM: urea plus chicken manure at 1 : 1 nitrogen basis)
The introduction of water-saving GCRPS technology has a high potential to increase rice grain yields and to significantly reduce irrigation water demand for rice cultivation. It remains unknown if this new rice production technique will in the end not lead to pollution swapping of greenhouse gases (GHGs) emissions, i.e., from CH4 emissions for conventional paddy fields to increased soil N2O and CO2 emissions for ground cover rice production systems
Summary
Atmospheric methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2) are key compounds in biogeochemical carbon and nitrogen cycling, thereby playing important roles for atmospheric chemistry and climate change (IPCC, 2007). Agriculture, without considering land use change, has been estimated to contribute approximately 10–12 % of the total global anthropogenic emissions of greenhouse gases (GHGs), which accounts for about 50 and 60 % of global CH4 and N2O emissions, respectively (Smith et al, 2007). In agricultural soils, these GHGs are all produced or consumed as a result of soil microbial processes, but the magnitude of the fluxes depends heavily on agricultural systems Measurements of GHG fluxes from different rice-based cropping systems are of regional and global significance
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