Urea deep placement reduces yield-scaled greenhouse gas (CH4 and N2O) and NO emissions from a ground cover rice production system

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.

Deep N fertilizer placement mitigated N2O emissions in a Swedish field trial with cereals

“…Aside from the differences in the water regimes between the abovementioned studies on rice cultivation and the results presented here, the definition of what is considered a deep placement is quite relative and varies between studies. For example, Schutz et al (1989) and Yao et al (2017) studied a placement depth of 0.20 and 0.10-0.15 m, respectively, which is comparable to the DP treament presented in this study. By contrast, Rath et al (1999) considered 0.05 m to be a deep placement, which is analogous to our SP treatment.…”

Simultaneous quantification of N2, NH3 and N2O emissions from a flooded paddy field under different N fertilization regimes

“…Nevertheless, the incorporation of N fertilizer in the deeper soil layers also stimulated N 2 O production from nitrification–denitrification processes compared with the control plots (Figure ). Water saturation in soils slows or even prevents the diffusion of N 2 O produced in deeper soil layers (Yao et al, ), which might lead to the further reduction of N 2 O to N 2 prior to its release to the atmosphere (Butterbach‐Bahl et al, ; Davidson, Keller, Erickson, Verchot, & Veldkamp, ).…”

“…A meta‐analysis conducted by Xia, Lam, et al () demonstrated that the incorporation of N fertilizer into the soil significantly decreased the emission of NH 3 from paddy fields by 26.4% and increased the yield of rice by 7.0%. Yao et al () reported that using a slow‐release urea fertilizer incorporated into the soil decreased N 2 O emissions from paddy fields by 40.9%–56.8%.…”

Elevated atmospheric CO2 reduces yield‐scaled N2O fluxes from subtropical rice systems: Six site‐years field experiments

“…Thus, integrating the findings of effects on N 2 O (this study) and CH 4 (Zheng et al., 2006) shows that total non‐CO 2 GHG emissions from rice systems will rise with increasing atmospheric CO 2 , but that the ‐induced reductions in soil N 2 O emissions negate as much as 24% of the increases in soil CH 4 emissions. However, this increase in non‐CO 2 GHG emissions from rice systems under can be significantly reduced by improving water regimes and using alternative fertilization practices such as alternate wetting and drying irrigation schemes, ground cover rice production system and urea deep placement (Beach et al., 2008; Linquist et al., 2015; Yao, Zheng, Liu, et al, 2017; Yao, Zheng, Zhang, et al, 2017). Also, adopting rice cultivars with potentially strong responses to may eventually not only improve crop yield but also enhance soil C sequestration (Hu et al., 2020), thereby curbing the future growth of greenhouse effect contributed by rice systems.…”