Abstract Controlling nitrogen (N) losses from pig slurry (PS) is a challenge under no-till because amendments are left on the soil surface. We investigated the potential of shallow injection of PS, with and without addition of the nitrifcation inhibitor dicyandiamide (DCD), to abate gaseous ammonia (NH 3 ) and nitrous oxide (N 2 O) emissions in winter crops in subtropical soils. Injection was compared with surface broadcasting of PS, with and without DCD. The signifcance of winter season on annual N 2 O emissions was assessed. Injecting PS reduced NH 3 volatilization compared with surface application. However, this reduction was partly ofset because N 2 O emissions increased by 77% (+1.53 kg N 2 O-N ha −1 ) when PS was injected. Adding DCD to injected PS reduced N 2 O emission below levels of surface-broadcast PS without the inhibitor, indicating that DCD may be a management option when injecting PS. Compared with a reference urea treatment, PS without DCD increased cumulative N 2 O emissions 5.7-fold (from 613 to 3515 g N 2 O-N ha −1 ) when injected, and 3.2-fold (from 613 to 1980 g N 2 O-N ha −1 ) when surface applied. Adding DCD signifcantly reduced emissions with injected PS, whereas reduction was not always signifcant with surface-applied PS. Nitrous oxide emissions during the winter cropping season contributed 30 to 44% of annual emissions, indicating that controlling gaseous N losses in that season is required to reduce the environmental footprint of the whole cropping system. Overall, combining PS injection with DCD was an efcient practice for reducing winter-season gaseous N losses from no-till soils under subtropical climate. Winter-Season Gaseous Nitrogen Emissions in Subtropical Climate: Impacts of Pig Slurry Injection and Nitrifcation Inhibitor Celso Aita,* Martin H. Chantigny, Rogério Gonzatto, Ezequiel C.C. Miola, Philippe Rochette, Stefen B. Pujol, Daniela B. dos Santos, Diego A. Giacomini, and Sandro J. Giacomini T he majority of pig slurry (PS) nitrogen (N) is in the ammoniacal form at time of application. Tis form is readily available to plants, but prone to environmental losses through several pathways. Te pH of PS is usually alkaline, facilitating ammonia (NH 3 ) volatilization when exposed to the atmosphere. Generally, greater volatilization occurs when PS is surface applied to soil with reduced infltration rate (Rochette et al., 2001; Chantigny et al., 2004). Alternatively, PS-N can be nitrifed to nitrate (NO 3 − ) and either leached to ground and sur- face waters, or denitrifed with associated production of nitrous oxide (N 2 O), a potent greenhouse gas. Field application of PS poses several challenges, especially in felds under no-till where incorporation in soil is incompatible with maintaining crop residues on the soil surface. Injection of PS in narrow bands has been used to reduce NH 3 volatilization with minimal disturbance of soil surface (Maguire et al., 2011; Dell et al., 2012; Aita et al., 2014). However, subsurface manure banding ofen stimulates N 2 O production by concentrating N and available carbon (C) in a limited volume of soil where anoxic conditions can develop (Comfort et al., 1988, 1990; Dell et al., 2011). Accordingly, greater soil N 2 O emissions have been reported with injection of pig (Chantigny et al., 2010; Velthof and Mosquera, 2011; Aita et al., 2014) and cattle slurries (Ellis et al., 1998; Möller and Stinner, 2009) as compared with surface application. However, similar N 2 O losses between the two application methods have also been reported (Dendooven et al., 1998a; Vallejo et al., 2005; Tomsen et al., 2010). Moreover, Sistani et al. (2010) reported both greater and smaller emissions with injection than surface application of PS, depending on year. Tese interannual diferences were attributed to diferences in rainfall distribution and interactions between envi- ronmental conditions (climate and soil) and slurry characteristics (dry matter content and rate of application). Te addition of nitrifcation inhibitors has been proposed to reduce N 2 O production in soil. Akiyama et al. (2010) estimated that emissions from agricultural felds were reduced by an aver- age of 38% for a range of organic and mineral N sources treated Abbreviations: DCD, dicyandiamide; EF, emission factor; IPCC, Intergovernmental Panel on Climate Change; PS, pig slurry; PSi, injection of pig slurry; PSs, surface broadcast of pig slurry; WFPS, water-flled pore space. C. Aita, R. Gonzatto, S.B. Pujol, D.A. Giacomini, and S.J. Giacomini, Dep. of Soil Science, Federal Univ. of Santa Maria, 97105-900, Santa Maria, Rio Grande do Sul, Brazil; M.H. Chantigny and P. Rochette, Agriculture and Agri-Food Canada, Québec Research and Development Centre, 2560 Hochelaga Blvd., Québec, QC, Canada, G1V 2J3; E.C.C. Miola, Institute of Biological Sciences, Federal Univ. of Rio Grande, 96170-000 São Lourenço do Sul, Rio Grande do Sul , Brazil; D.B. dos Santos, Federal Institute of Education, Science and Technology of Rio Grande do Sul, 99170-000 Sertão, Rio Grande do Sul, Brazil. Assigned to Associate Editor Mindy Spiehs. © 2019 The Author(s). Re-use requires permission from the publisher. J. Environ. Qual. doi:10.2134/jeq2018.04.0137 Supplemental material is available online for this article. Received 11 May 2018. Accepted 29 May 2019. *Corresponding author (celsoaita@gmail.com). Journal of Environmental Quality ATMOSPHERIC POLLUTANTS AND TRACE GASES TECHNICAL REPORTS Core Ideas • Winter-season NH 3 and N 2 O were measured after pig slurry ad- ditions to no-till soils. • N 2 O emissions during the winter season contributed 30 to 44% of annual emissions. • Shallow injection of pig slurry reduced NH 3 volatilization but increased N 2 O emissions. • DCD added to pig slurry more than ofset the increase in N 2 O emissions with injection. • Pig slurry injection combined with DCD reduces gaseous N losses in subtropical soils. Published online July 11, 2019