Meta-Analysis of Strategies to Reduce NH3 Emissions from Slurries in European Agriculture and Consequences for Greenhouse Gas Emissions

Abstract

The intensification of livestock production, to accommodate rising human population, has led to a higher emission of ammonia into the environment. For the reduction of ammonia emissions, different management steps have been reported in most EU countries. Some authors, however, have criticized such individual measures, because attempts to abate the emission of ammonia may lead to significant increases in either methane, nitrous oxide, or carbon dioxide. In this study, we carried out a meta-analysis of experimental European data published in peer-reviewed journals to evaluate the impact of major agricultural management practices on ammonia emissions, including the pollution swapping effect. The result of our meta-analysis showed that for the treatment, storage, and application stages, only slurry acidification was effective for the reduction of ammonia emissions (−69%), and had no pollution swapping effect with other greenhouse gases, like nitrous oxide (−21%), methane (−86%), and carbon dioxide (−15%). All other management strategies, like biological treatment, separation strategies, different storage types, the concealing of the liquid slurry with different materials, and variable field applications were effective to varying degrees for the abatement of ammonia emission, but also resulted in the increased emission of at least one other greenhouse gas. The strategies focusing on the decrease of ammonia emissions neglected the consequences of the emissions of other greenhouse gases. We recommend a combination of treatment technologies, like acidification and soil incorporation, and/or embracing emerging technologies, such as microbial inhibitors and slow release fertilizers.

Effects of slurry acidification on soil N2O fluxes and denitrification

“…Therefore, we stay critical with regard to the results of a meta‐analysis by Emmerling et al. (2020) who concluded that applications of acidified slurry may not result in stimulation of soil N 2 emission, specifically as details of the underlying studies, which were anyhow small in numbers (2–7), are not displayed in detail. However, there is compelling evidence, also observed in our study, that slurry acidification results in higher soil N availability, which is known to promote crop growth for example, of winter wheat, spring barley or maize (Birkmose & Vestergaard 2013; Fangueiro et al.…”

“…In order to reduce the emissions of NH 3 , different national and international directives are in place (e.g., DEFRA, 2018; Guthrie et al., 2018; United Nations Economic Commission for Europe, 2015) which include practices to mitigate NH 3 losses from agricultural sources. Practices discussed to reduce NH 3 volatilization following slurry application to agricultural lands are dilution of slurries, addition of acids, salts and formalin, direct injection of slurry in the soil or timing of slurry/ manure spreading (Bussink & Oenema 1998; Emmerling et al., 2020; Hou et al., 2015; Seidel et al., 2017; Sommer & Jensen 1994; Velthof et al., 1990; Whitehead & Raistrick 1990). However, practices regarding incorporation of slurry into the soil and better timing of slurry applications in response to plant nutrient demands, for example, via split application, can be cost and time intensive for small farms.…”

“…Though the use of acids has proven to be a valid strategy to mitigate NH 3 losses due to slurry spreading (e.g., Emmerling et al., 2020; Kai et al., 2008; Park et al., 2018; Sindhöj et al. 2019), a limited number of studies have focused on the potential consequences of acidified slurry applications on N 2 O emissions in soil (e.g., Emmerling et al., 2020; Seidel et al., 2017). In a review on animal slurry acidification, Fangueiro et al.…”

“…However, a few more studies were published after 2015 (e.g., Fangueiro et al., 2016; Seidel et al., 2017), while Emmerling et al. (2020) concluded on a limited of published studies that slurry acidification may result in an approximately 20% reduction of soil N 2 O emissions.…”

A Review of Crop Husbandry and Soil Management Practices Using Meta-Analysis Studies: Towards Soil-Improving Cropping Systems

“…Nitrous oxide emissions from cropland increase with nitrogen fertilization, but the increase can be mitigated through better compliance with fertilizer recommendations, and the use of nitrification inhibitors and biochar [72]. Slurry acidification, deep placement, and urease inhibitors decreases ammonia emissions from slurries and urea fertilizers applied to soil [76,86]. No meta-analysis studies related to the effectiveness of manure products from different manure processing techniques [87].…”