Nitrous oxide and methane fluxes from plasma-treated pig slurry applied to winter wheat

Nutr Cycl Agroecosyst https://doi.org/10.1007/s10705-024-10363-8 ORIGINAL ARTICLE Nitrous oxide and methane fluxes from plasma‑treated pig slurry applied to winter wheat I. L. Lloyd · R. P. Grayson · M. V. Galdos R. Morrison · P. J. Chapman · Received: 24 August 2023 / Accepted: 25 May 2024 © The Author(s) 2024 Abstract The use of livestock waste as an organic fertiliser releases significant greenhouse gas emissions, exacerbating climate change. Innovative fertiliser management practices, such as treating slurry with plasma induction, have the potential to reduce losses of carbon and nitrogen to the environment. The existing research on the effectiveness of plasma-treated slurry at reducing nitrous oxide (N2O) and methane (CH4) emissions, however, is not comprehensive, although must be understood if this technology is to be utilised on a large scale. A randomised block experiment was conducted to Supplementary Information The online version contains supplementary material available at https://doi. org/10.1007/s10705-024-10363-8. I. L. Lloyd (*) · R. P. Grayson · P. J. Chapman School of Geography, University of Leeds, Leeds LS2 9JT, UK e-mail: R. P. Grayson e-mail: P. J. Chapman e-mail: M. V. Galdos Rothamsted Research, Harpenden AL5 2JQ, UK e-mail: R. Morrison UK Centre for Ecology and Hydrology, Wallingford OX10 8BB, UK e-mail: measure soil fluxes of N 2O and C H4 from winter wheat every two hours over an 83-day period using automated chambers. Three treatments receiving a similar amount of plant-available N were used: (1) inorganic fertiliser (IF); (2) pig slurry combined with inorganic fertiliser (PS); (3) plasma-treated pig slurry combined with inorganic fertiliser (TPS). Cumulative N2O fluxes from TPS (1.14 g N m−2) were greater than those from PS (0.32 g N m−2) and IF (0.13 g N m−2). A diurnal pattern in N 2O fluxes was observed towards the end of the experiment for all treatments, and was driven by increases in waterfilled pore space and photosynthetically active radiation and decreases in air temperature. Cumulative CH4 fluxes from PS (3.2 g C m−2) were considerably greater than those from IF (− 1.4 g C m−2) and TPS (− 1.4 g C m−2). The greenhouse gas intensity of TPS (0.2 g CO2-eq kg grain−1) was over twice that of PS (0.07 g CO2-eq kg grain−1) and around six times that of IF (0.03 g CO2-eq kg grain−1). Although treating pig slurry with plasma induction considerably reduced CH4 fluxes from soil, it increased N2O emissions, resulting in higher non-CO2 emissions from this treatment. Life-cycle analysis will be required to evaluate whether the upstream manufacturing and transport emissions associated with inorganic fertiliser usage are outweighed by the emissions observed following the application of treated pig slurry to soil. Vol.: (0123456789) 13 Nutr Cycl Agroecosyst Keywords Agriculture · Automated chamber · Carbon dioxide · Greenhouse gases · Greenhouse gas intensity · Non-CO2 greenhouse gases · Organic fertiliser · Trade-offs Introduction Nitrogen (N) is one of the most limiting nutrients for crop growth in agricultural soils, so organic (i.e., animal manure and slurry) and inorganic (i.e., synthetic) N fertilisers are applied to provide a supply of N to support crop growth and achieve high yields (Lu et al. 2021). Organic fertilisers also provide a source of other plant nutrients, enhance soil carbon (C) content, and are increasingly being seen as part of an on-farm circular economy within the agricultural sector. The use of fertilisers in agriculture results in significant emissions of greenhouse gases (GHGs) to the atmosphere. Agriculture is responsible for 13% global carbon dioxide (CO2) emissions, 50% global methane (CH4) emissions, and 60% global nitrous oxide (N2O) emissions (Macharia et al. 2020). Nitrous oxide and CH4 are of particular concern, as they have global warming potentials 273 and 27.9 times greater than CO2 respectively (Smith et al. 2021) and continue to exacerbate climate change (Mikhaylov et al. 2020). Agricultural N2O emissions primarily originate from the use of inorganic and organic N fertilisers, which has increased markedly over the last 60 years (Rudaz et al. 1999; Cameron et al. 2013; Lu et al. 2021). Between 2016 and 2019, animal farming in the European Union produced more than 1.4 billion tonnes of manure annually, and over 90% of this was directly re-applied to soils (Koninger et al. 2021). Fertiliser application, particularly organic fertiliser, can also increase CH4 emissions; CH4 is often produced during organic fertiliser storage, as the C supply and storage conditions facilitate methanogenesis, dissolving CH4 into the fertiliser and releasing it upon application to soil (Rochette and Cote 2000; Bastami et al. 2016). There is an urgent need to minimise the negative impacts of agriculture on the environment, with the aim to achieve net zero GHG emissions becoming increasingly critical (Sakrabani et al. 2023). Despite the implementation of strategies which aim to reduce environmental N pollution (i.e., Nitrate Vulnerable Zones (UK Government 2021) and 4R Vol:. (1234567890) 13 Nutrient Stewardship — right source, rate, time and place (Nutrient Stewardship 2017)), GHG emissions from agriculture, particularly N2O, remain high (Tian et al. 2020). To reduce GHG emissions from fertiliser use, crop N use efficiency (NUE) — the efficiency at which applied N is assimilated by plants (Sharma and Bali 2018) — must be improved. Given the push to increase the use of livestock waste as fertiliser and build soil C, a range of practices and innovative technologies are promoted to reduce GHG emissions from fertiliser use and improve NUE. One such example of this is the treatment of organic fertilisers, such as pig slurry, with plasma induction. This treatment primarily aims to reduce losses of the non-GHG ammonia (NH3) by ionising air to form reactive nitrogen gas which is absorbed into the slurry, creating an N-rich slurry (Nyang’au et al. 2024). This process lowers the pH of the slurry and reduces the potential for NH3 emissions (Nyang’au et al. 2024). An increase in the N content of the plasma-treated slurry means the product has the potential to replace synthetic inorganic fertiliser and has been shown to increase yields compared to untreated slurry (Mousavi et al. 2022; Cottis et al. 2023), as well as reducing both CH4 and NH3 emissions during storage (Graves et al. 2018). Whether the beneficial gains of increasing the amount of inorganic N available for immediate plant uptake are counterbalanced by other N losses upon application to the soil, such as N2O to the atmosphere, however, are unknown. Numerous studies have investigated the impacts of fertiliser application on GHG fluxes, mainly N 2O, from agricultural soils (Inselsbacher et al. 2010; Mateo-Marin et al. 2020; Adelekun et al. 2021). The overarching consensus is that soils amended with organic fertiliser have higher N 2O and CH4 emissions than those am (...truncated)