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We measured denitrification and nitrous oxide (N 2 O) emissions from subtropical maize-winter wheat cropping systems in the Sichuan Basin, Southwestern China between 2005 and 2006, providing a dataset that enabled us to comprehensively test the non-linear empirical NOE v2 model. The primary aims were to (i) quantify annual denitrification and N 2 O emissions from intensively managed agroecosystems, (ii) parameterize the denitrification sub-model in NOE v2 with site-specific measurements and incubations and (iii) evaluate NOE v2 in a subtropical area in particular. Field measurements were conducted at two adjacent sites (hereafter named NR and NF, respectively). At site NR, soils were fertilized with urea at 150 (NR-150) and 250 (NR-250) kg N ha −1 crop −1 . At site NF, soils were fertilized with urea (NF-U), ammonium sulphate (NF-AS) and potassium nitrate (NF-KN) at 150 kg N ha −1 crop −1 . Set-aside soils were incubated in laboratory to determine two biological parameters of the NOE v2 model namely the potential denitrification rate ( D p ) and the maximal fraction of N 2 O production through denitrification ( r max ). With respect to subtropical climate, we modified the response function linked to soil temperature using an equation based on temperature sensitivity ( Q 10 ). The incubated D p and r max were 2.96 kg N ha −1 d −1 and 0.60, respectively. A Q 10 value of 2.95 was estimated from the exponential relationship between soil heterotrophic respiration rates and soil temperature (5 cm depth) throughout the experimental period ( r 2 = 0.84, n = 96, p = 0.000). Varying across the treatments, the observed and simulated denitrification rates ranged from 10.95 to 15.38 and from 12.47 to 14.91 kg N ha −1 yr −1 , respectively. The simulations were averagely 3% larger than the observations (ranging from −20 to 27%). Accordingly, the observed and simulated N 2 O emissions ranged from 1.45 to 2.72 and from 1.38 to 2.21 kg N ha −1 yr −1 , respectively. The simulations were averagely 9% lower than the observations (ranging from −19 to 7%). We conclude that NOE v2 is applicable to the studied subtropical area with site-specific parameterization. Modification of the response function linked to soil temperature seems essential to apply the model to a wide range of climate conditions. [ABSTRACT FROM AUTHOR]

China is regarded as one of the nitrogen deposition hotspots in the world. Measurements to-date have focused mainly on the North China Plain, ignoring the fact that atmospheric chemical and physical properties vary across the country and that there may be other hotspots regions that should be investigated. For this reason we have conducted a six year study, measuring the bulk deposition of reduced (NH 4 -N), oxidized (NO 3 -N), and dissolved organic nitrogen (DON) at three contrasting sites in the Sichuan province, southwest China. The study sites were a high altitude forest in the Gongga Mountains (GG), an agriculture dominated region in Yanting (YT) and an urban site in the mega city Chengdu (CD). The annual average bulk deposition fluxes of total dissolved nitrogen (TDN) were 7.4, 23.1 and 36.6 kg N ha -1 yr -1 at GG, YT and CD sites, respectively, during the study period 2008 to 2013. The contributions of NH 4 -N, NO 3 -N and DON to the TDN were in the range of 48.4-57.8%, 28.8-43.7%, and 8.0-15.6%, respectively. DON bulk deposition was mainly dominated by agricultural activities. TDN bulk deposition fluxes showed increasing trends at the agricultural and urban sites from 2008 to 2013, but there was little change at the remote forest (GG) site. While reduced N dominated bulk N deposition at all the three sites, its contribution showed a decreasing trend, suggesting a gradual increase in the importance of oxidized N. These results reveal the value of long term monitoring in detecting changes in the atmospheric chemical composition of this rapidly changing region, and their inclusion in the policy debate regarding which sources should be controlled in order to reduce the long term impacts of N deposition, especially for southwest China, where there are few measurements of N deposition., (Copyright © 2017 Elsevier Ltd. All rights reserved.)