N 2 O emissions from different land uses in mid-subtropical China Shan Lin 1 , Javed Iqbal 1 , Ronggui Hu *, Minglei Feng College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, PR China 1. Introduction Agricultural activities have greatly altered the global nitrogen cycle and produced a great deal of nitrous oxide (N 2 O) through crop cultivation, N fertilizer application, burning of agricultural residue, animal manure composting, etc. (Dong et al., 2007). N 2 O emissions grew by about 50%, due mainly to increased use of fertilizer and the growth of agriculture (IPCC, 2007). Of global anthropogenic emissions in 2005, agriculture accounted for about 60% of N 2 O(IPCC, 2007). In China, agriculture is responsible for about 36% of N 2 O emissions (ADB-GEF-UNEF, 1998). Although these percentages are lower than the world’s average values, they represent considerable amounts with a range of 70–190 Gg N 2 O-N (ADB-GEF-UNEF, 1998). The increasing atmospheric N 2 O concentrations have raised concerns about potential global warming and the possible positive feedback effects that warming could have on further fluxes between soil and atmosphere (Rustad et al., 2000). Researchers have emphasized the importance of improving our understanding of soil processes in order to gain more confidence in projections about future changes in the global atmospheric N 2 O concentra- tions (Merino et al., 2004). Recently, some researchers have shown great interest to estimate the N 2 O emissions from various Chinese croplands including rice–wheat rotation (Kreye et al., 2007), vegetable field (He et al., 2009), rice paddies (Zou et al., 2007), maize–wheat rotation (Ding et al., 2007), the natural wetlands (Wang et al., 2007) and the semi-arid grassland (Zhang and Han, 2008). However, effects of land use on changes of N 2 O emissions from soils in subtropical area of South China are poorly understood. In addition, N 2 O emissions from agroecosystems might be under- estimated because the sources and sinks of N 2 O are not well characterized (Chen et al., 2000). To accurately quantify N 2 O emissions from agroecosystems, multiple factors must be taken into account, including soil properties, climatic conditions, agricultural practices and the impacts of vegetation, etc. (Yanai et al., 2003). Since the subtropical climate is characterized typically by rainy and dry seasons, seasonal patterns of the N 2 O emissions are important for our understanding of how soil Agriculture, Ecosystems and Environment 136 (2010) 40–48 ARTICLE INFO Article history: Received 10 June 2009 Received in revised form 30 October 2009 Accepted 2 November 2009 Available online 5 December 2009 Keywords: Land use N 2 O fluxes Seasonal difference Soil inorganic N Subtropical Three Gorges Reservoir Area ABSTRACT Agricultural soils are primarily responsible for the global anthropogenic nitrous oxide (N 2 O) emissions due to excessive use of N fertilizers. Along with fertilizer, it may also be excelled by the seasonal precipitation pattern of monsoon climate in Southern China. To estimate N 2 O emissions of native and agricultural soils in subtropical ecosystem surrounding Three Gorges Dam, a 4 years campaign was started to determine the temporal N 2 O fluxes from seven sites of four land use types (one vegetable field, three uplands, two orchards and one pine forest). The mean annual budget of N 2 O emissions was 0.13– 5.27 kg N 2 O-N ha 1 year 1 . Pine forest had significantly lower N 2 O emissions than agriculture land uses. Tilled orchard had significantly lower N 2 O emissions than non-tilled orchard. Generally, among agriculture land uses, maximum N 2 O emissions were observed from vegetable field followed by orchards and uplands. Among all land uses, N 2 O emissions were significantly correlated with amount of N fertilizer applied. Every year, the climate was warm and wet from April through September (the hot– humid season) and became cool and dry from October through March (the cool–dry season). N 2 O fluxes and environmental variables (soil temperature, water-filled pore space (WFPS), soil NO 3  -N and NH 4 + -N contents) had significant seasonal variabilities. Driven by seasonality of soil temperature, WFPS, soil NO 3  -N and NH 4 + -N contents, N 2 O fluxes were significantly higher in the hot–humid season than in the cool–dry season. The relationship between N 2 O fluxes and all the environmental variables were presented in one linear model of variation which explained 72–97% of N 2 O flux variability among different land uses. We conclude that N 2 O fluxes from different land uses are strongly under control of different climatic predictors along with soil nutrient status, which interact in conjunction with each other to supply the readily available substrates for the N 2 O flux from the subtropical soils. ß 2009 Elsevier B.V. All rights reserved. * Corresponding author at: Room # 509, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, Hubei, PR China. Tel.: +86 27 87282152; fax: +86 27 87396057. E-mail addresses: solvia_uaf@yahoo.com (J. Iqbal), hronggui@163.com (R. Hu). 1 These authors contributed equally to this work. Contents lists available at ScienceDirect Agriculture, Ecosystems and Environment journal homepage: www.elsevier.com/locate/agee 0167-8809/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2009.11.005