Food production systems associated with livestock management are significant sources of greenhouse gases (GHGs), contributing about 12% of the annual global anthropogenic emissions (Havlik et al.,2014). Urine and dung deposition by grazing livestock on pasture soils, manure management, and ruminant enteric fermentation are the primary sources of the GHGs; methane (CH4) and carbon dioxide (CO2), and nitrous oxide (N2O) (Tubiello et al.,2014; Herrero et al., 2016; Tully et al., 2017; Zhu et al., 2020). In grazed pastures, livestock excreta create patches of nutrient-rich soils, stimulating microbial activities and enhancing GHG emissions (Charteris et al., 2021: López-Aizpún et al., 2020).
The deposition of urine and fresh dung by grazing livestock in intensively grazed pastures may increase soil moisture and subsequently increase anaerobic microsites, for N2O-producing processes, i.e., denitrification (Cardoso et al., 2019; Marsden et al., 2016; Wen et al., 2021). The decomposition and mineralization of deposited dung and the locally added organic carbon (C) may also result in CH4 and CO2 production and emission “hotspots” in intensively grazed pastures (Clemens and Ahlgrimm, 2001; Saggar et al., 2014).
Globally, methane from livestock systems comprises 46% of all agricultural GHG emissions (Herrero et al., 2013) and has a global warming potential (GWP) ~ 27-times that of CO2 over a 100-year horizon (IPCC, 2021). Carbon dioxide is one of the globally important greenhouse gases contributing to the greenhouse effect, and its atmospheric concentrations reaching 419.3 ppm in 2022, which is 51%above the pre-industrial levels (278 around 1750) (Friedlingsten et al., 2023). Increases in atmospheric CH4 and CO2 have significant effects on global climate change. On the other hand, research on the dynamics of these C-GHGs has received far less attention that the N2O emissions from these sources (Rivera and Chará, 2021), and especially following the application of a urine and dung as well the use of a nitrification inhibitor. Also, nitrification inhibitors (NI’s), including dicyandiamide (DCD), have been well-documented in their role in reducing nitrate (NO3−) leaching and N2O emissions from urine deposition (Luo et al., 2016; Moir et al.,2016; Monoghan et al., 2009). However, the role of DCD has seldom been explored on its influence on the dynamics of C-GHGs upon urine and lung deposition. This is despite the evidence that DCD controls soil N2O by delaying nitrification, retaining nitrogen (N) in the more immobile ammonium (NH4+) in the soil, and reducing NO3− concentrations (Amberger, 1989), consequently reducing denitrification rates and N2O emissions (Luo et al., 2016). On the other hand, soil NH4+ is known to inhibit CH4 oxidation (Hutsch, 1998; Kravchenko et al., 2002; Tlustos et al., 1998), often resulting in a net increase in CH4 emitted from soil (Bronson and Mosier, 1994).
Thus, it is imperative to understand the dynamics of these GHGs in livestock-grazed pastures in order to better quantify their potential contribution to total GHGs, and to understand the effects of using DCD, a NI on the dynamics and extent of soil-borne CH4 and CO2 fluxes. Therefore, this paper aims to (i) clarify the soil and environmental controls of soil CH4 and CO2 fluxes from cattle urine with and without the nitrification inhibitor, DCD, and dung deposited onto grassland soil.