Abstract
Ground cover rice production system (GCRPS), i.e., paddy soils being covered by thin plastic films with soil moisture being maintained nearly saturated status, is a promising technology as increased yields are achieved with less irrigation water. However, increased soil aeration and temperature under GCRPS may cause pollution swapping in greenhouse gas (GHG) from CH4 to N2O emissions. A 2-year experiment was performed, taking traditional rice cultivation as a reference, to assess the impacts of N-fertilizer placement methods on CH4, N2O and NO emissions and rice yields under GCRPS. Averaging across all rice seasons and N-fertilizer treatments, the GHG emissions for GCRPS were 1973 kg CO2-eq ha−1 (or 256 kg CO2-eq Mg−1), which is significantly lower than that of traditional cultivation (4186 kg CO2-eq ha−1or 646 kg CO2-eq Mg−1). Furthermore, if urea was placed at a 10–15 cm soil depth instead of broadcasting, the yield-scaled GHG emissions from GCRPS were further reduced from 377 to 222 kg CO2-eq Mg−1, as N2O emissions greatly decreased while yields increased. Urea deep placement also reduced yield-scaled NO emissions by 54%. Therefore, GCRPS with urea deep placement is a climate- and environment-smart management, which allows for maximal rice yields at minimal GHG and NO emissions.
Highlights
ground cover rice production system (GCRPS) may cause pollution swapping in greenhouse gas (GHG) from CH4 to N2O emissions
As CH4 emissions in GCRPS systems are already low, total Greenhouse gas (GHG) mitigation must be achieved by a reduction in N2O emissions, which points towards improved N fertilizer management
We present the results of a 2-year field measurement in which CH4, N2O and nitric oxide (NO) fluxes as well as rice yields were determined simultaneously for the water-saving ground cover rice production system as well as for the traditional rice cultivation to identify potential GHG mitigation effects of urea deep placement
Summary
GCRPS may cause pollution swapping in greenhouse gas (GHG) from CH4 to N2O emissions. In a recent meta-analysis study, Linquist et al.[4] provided evidence that GHG (CH4 and N2O) emissions from paddy rice cultivations are roughly four times higher than those originating from the production of other cereals such as wheat or maize. In view of such high GHG emissions from rice production systems, there is strong interest in its mitigation. As most CH4 mitigation strategies for rice production systems are based on water management and periodical soil aeration, trade-offs with regard to N-trace gas (namely N2O and NO) emissions, which might be stimulated under increased soil aeration, need to be considered to avoid significant pollution swapping. As CH4 emissions in GCRPS systems are already low, total GHG mitigation must be achieved by a reduction in N2O emissions, which points towards improved N fertilizer management
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