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Greenhouse gas emissions from rice paddies under sewage irrigation deserve much attention since domestic sewage effluents are increasingly used for agriculture in developing countries. A field experiment was conducted to simultaneously measure methane (CH4) and nitrous oxide (N2O) emissions from rice (Oryza sativa L.) paddies under sewage and unpolluted river water irrigation in southeast China. The rice paddies were under a local typical water regime, which was characterized by flooding–midseason drainage–reflooding–moist intermittent irrigation but without water logging. Relative to unpolluted river water irrigation, sewage irrigation significantly increased CH4 and N2O emissions from rice paddies. Seasonal fluxes of CH4 averaged 1.51mgm−2 h−1 for the plots irrigated by river water and 1.92mgm−2 h−1 for the plots irrigated by sewage. In contrast with river water irrigation, sewage irrigation increased CH4 by 27% and 33% for paddy plots with and without chemical N addition, respectively. Under sewage irrigation, seasonal fluxes of N2O-N averaged 26.79μgm−2 h−1 for the plots without N application and 74.07μgm−2 h−1 for the plots applied at the rate of 200kgNha−1. Relative to river water irrigation, sewage irrigation increased N2O by 68% and 170% for the plots with and without N application, respectively. The direct emission factor of fertilizer N for N2O was estimated to be 0.71% for the rice paddies under sewage irrigation and 0.52% for the plots irrigated by river water. Besides direct N2O emissions, N input by sewage irrigation induced substantial indirect N2O emission from rice paddies. The results of the net GWPs from CH4 and N2O indicate that sewage irrigation would intensify the radiative forcing of rice paddies with midseason drainage and moist irrigation... [Copyright &y& Elsevier]

The fruit has become the third-largest agricultural planting industry after cereals and vegetables in China. Fertilization regimes (e.g., application rate and method) in fruit orchards typically differ from cereal croplands, which would incur a pronounced difference in fertilizer-induced nitrous oxide (N 2 O) emissions between them. However, fertilizer-induced direct N 2 O emissions from orchard fields remain poorly understood. We conducted a field experiment in a peach orchard and a global meta-analysis of N 2 O emissions from fruit orchards. The emission factor (EF) of fertilizer N for N 2 O averaged 0.81%, with a background N 2 O emission of 3.4 kg N ha–1 yr-1 in our field study. A global meta-analysis suggested that the linear regression model was the best to fit N 2 O emissions by fertilizer N input for most fruit types compared to the nonlinear models. When averaging all global data, the linear model projected the EF of N 2 O from orchards to be 0.84%, with the background emission of 1.96 kg N ha–1. The estimate of direct N 2 O derived from the orchard-specific nonlinear model was substantially lower than those from the nonlinear model with global cropland measurements. The fertilizer-induced direct N 2 O emission from Chinese orchards during the 2000s was estimated to be 32–49 Gg N yr–1, equivalent to about 14% of total direct N 2 O emissions from Chinese uplands. Therefore, orchard cultivation constitutes a hotspot of N 2 O emissions in the agricultural sector, and priority should be given to emissions reduction to achieve the transition to climate-smart agriculture. [Display omitted] • N 2 O emissions from global orchards were summarized and meta-analyzed. • N 2 O emission was 32–49 Gg N yr–1 from Chinese orchards during the 2000s. • Orchard cultivation is one of the hotspots of agricultural N 2 O emissions. • Orchard N 2 O emissions were similar to emissions from vegetables and tea cultivation. [ABSTRACT FROM AUTHOR]

Biochar amendment has been shown to reduce nitrous oxide (N 2 O) emissions from acidic soils in tea plantations. Given that both soil bacterial and fungal denitrifications can produce N 2 O, their relative contributions to the decrease in N 2 O emissions following biochar amendment remain unclear. Here, we examined soils sampled from a subtropical tea plantation that had received 2 years of biochar amendment. Measurements of the relative contributions of fungi and bacteria to N 2 O production were taken by the substrate-induced respiration method implemented with the addition of selective inhibitors. The abundances of total fungi, bacteria, and key N 2 O-related bacterial genes were quantified by q-PCR, and the composition of the fungal community was analyzed by 18S rRNA amplicon sequencing. The results showed that the contribution of fungi to N 2 O production (52%) was greater than that of bacteria (18%) for the N-applied acidic soils. Biochar amendment significantly decreased the fungal abundances and the fungal contribution to N 2 O production (by 28%). In contrast, biochar amendment significantly increased the abundances of N 2 O-related bacteria (e.g., ammonia-oxidizing bacteria (AOB), nirS , nosZ). Structural equation models (SEMs) revealed that biochar decreased the fungal contribution to N 2 O production through enhancing the soil pH and shifting the fungal community composition. Our results highlight that the decreased N 2 O emissions could be ascribed to the stimulated N 2 O consumption process (driven by N 2 O-consuming bacteria encoded by the nosZ gene) and suppressed fungal dominance in acidic soils from tea plantations. This study presents relatively comprehensive insights into the regulatory roles of biochar on soil microbe-mediated N 2 O production processes. • Fungi played a more important role than bacteria in N 2 O production from acidic soils. • Biochar shifted the fungal community on genus level from acidic soils. • Biochar decreased the fungal contribution to N 2 O production. [ABSTRACT FROM AUTHOR]